diff --git a/src/misc/identifiable-error.ts b/src/misc/identifiable-error.ts
new file mode 100644
index 0000000000..1edd26cd18
--- /dev/null
+++ b/src/misc/identifiable-error.ts
@@ -0,0 +1,13 @@
+/**
+ * ID付きエラー
+ */
+export class IdentifiableError extends Error {
+	public message: string;
+	public id: string;
+
+	constructor(id: string, message?: string) {
+		super(message);
+		this.message = message;
+		this.id = id;
+	}
+}
diff --git a/src/server/activitypub/followers.ts b/src/server/activitypub/followers.ts
index 563b3da653..002576b2e7 100644
--- a/src/server/activitypub/followers.ts
+++ b/src/server/activitypub/followers.ts
@@ -48,7 +48,6 @@ export default async (ctx: Router.IRouterContext) => {
 	const partOf = `${config.url}/users/${userId}/followers`;
 
 	if (page) {
-		// Construct query
 		const query = {
 			followeeId: user._id
 		} as any;
diff --git a/src/server/activitypub/following.ts b/src/server/activitypub/following.ts
index f23e177e25..0d7486f68a 100644
--- a/src/server/activitypub/following.ts
+++ b/src/server/activitypub/following.ts
@@ -48,7 +48,6 @@ export default async (ctx: Router.IRouterContext) => {
 	const partOf = `${config.url}/users/${userId}/following`;
 
 	if (page) {
-		// Construct query
 		const query = {
 			followerId: user._id
 		} as any;
diff --git a/src/server/activitypub/outbox.ts b/src/server/activitypub/outbox.ts
index 8b65ce993a..ff8f884b19 100644
--- a/src/server/activitypub/outbox.ts
+++ b/src/server/activitypub/outbox.ts
@@ -78,7 +78,6 @@ export default async (ctx: Router.IRouterContext) => {
 		}
 		//#endregion
 
-		// Issue query
 		const notes = await Note
 			.find(query, {
 				limit: limit,
diff --git a/src/server/api/api-handler.ts b/src/server/api/api-handler.ts
index 0eef9ab5c7..39caba6b18 100644
--- a/src/server/api/api-handler.ts
+++ b/src/server/api/api-handler.ts
@@ -5,18 +5,17 @@ import authenticate from './authenticate';
 import call from './call';
 import { IUser } from '../../models/user';
 import { IApp } from '../../models/app';
+import { ApiError } from './error';
 
 export default async (endpoint: IEndpoint, ctx: Koa.BaseContext) => {
 	const body = ctx.is('multipart/form-data') ? (ctx.req as any).body : ctx.request.body;
 
-	const reply = (x?: any, y?: any) => {
-		if (x === undefined) {
+	const reply = (x?: any, y?: ApiError) => {
+		if (x == null) {
 			ctx.status = 204;
 		} else if (typeof x === 'number') {
 			ctx.status = x;
-			ctx.body = {
-				error: x === 500 ? 'INTERNAL_ERROR' : y
-			};
+			ctx.body = y;
 		} else {
 			ctx.body = x;
 		}
@@ -29,7 +28,11 @@ export default async (endpoint: IEndpoint, ctx: Koa.BaseContext) => {
 	try {
 		[user, app] = await authenticate(body['i']);
 	} catch (e) {
-		reply(403, 'AUTHENTICATION_FAILED');
+		reply(403, new ApiError({
+			message: 'Authentication failed. Please ensure your token is correct.',
+			code: 'AUTHENTICATION_FAILED',
+			id: 'b0a7f5f8-dc2f-4171-b91f-de88ad238e14'
+		}));
 		return;
 	}
 
@@ -39,7 +42,11 @@ export default async (endpoint: IEndpoint, ctx: Koa.BaseContext) => {
 	try {
 		res = await call(endpoint.name, user, app, body, (ctx.req as any).file);
 	} catch (e) {
-		reply(400, e);
+		if (e.kind == 'client') {
+			reply(400, e);
+		} else {
+			reply(500, e);
+		}
 		return;
 	}
 
diff --git a/src/server/api/call.ts b/src/server/api/call.ts
index 8efc679603..2b447b30f6 100644
--- a/src/server/api/call.ts
+++ b/src/server/api/call.ts
@@ -2,6 +2,15 @@ import limiter from './limiter';
 import { IUser } from '../../models/user';
 import { IApp } from '../../models/app';
 import endpoints from './endpoints';
+import { ApiError } from './error';
+import { apiLogger } from './logger';
+import { Response } from './define';
+
+const accessDenied = {
+	message: 'Access denied.',
+	code: 'ACCESS_DENIED',
+	id: '56f35758-7dd5-468b-8439-5d6fb8ec9b8e'
+};
 
 export default async (endpoint: string, user: IUser, app: IApp, data: any, file?: any) => {
 	const isSecure = user != null && app == null;
@@ -9,31 +18,43 @@ export default async (endpoint: string, user: IUser, app: IApp, data: any, file?
 	const ep = endpoints.find(e => e.name === endpoint);
 
 	if (ep == null) {
-		throw 'ENDPOINT_NOT_FOUND';
+		throw new ApiError({
+			message: 'No such endpoint.',
+			code: 'NO_SUCH_ENDPOINT',
+			id: 'f8080b67-5f9c-4eb7-8c18-7f1eeae8f709',
+		});
 	}
 
 	if (ep.meta.secure && !isSecure) {
-		throw 'ACCESS_DENIED';
+		throw new ApiError(accessDenied);
 	}
 
 	if (ep.meta.requireCredential && user == null) {
-		throw 'CREDENTIAL_REQUIRED';
+		throw new ApiError({
+			message: 'Credential required.',
+			code: 'CREDENTIAL_REQUIRED',
+			id: '1384574d-a912-4b81-8601-c7b1c4085df1',
+		});
 	}
 
 	if (ep.meta.requireCredential && user.isSuspended) {
-		throw 'YOUR_ACCOUNT_HAS_BEEN_SUSPENDED';
+		throw new ApiError(accessDenied, { reason: 'Your account has been suspended.' });
 	}
 
 	if (ep.meta.requireAdmin && !user.isAdmin) {
-		throw 'YOU_ARE_NOT_ADMIN';
+		throw new ApiError(accessDenied, { reason: 'You are not the admin.' });
 	}
 
 	if (ep.meta.requireModerator && !user.isAdmin && !user.isModerator) {
-		throw 'YOU_ARE_NOT_MODERATOR';
+		throw new ApiError(accessDenied, { reason: 'You are not a moderator.' });
 	}
 
 	if (app && ep.meta.kind && !app.permission.some(p => p === ep.meta.kind)) {
-		throw 'PERMISSION_DENIED';
+		throw new ApiError({
+			message: 'Your app does not have the necessary permissions to use this endpoint.',
+			code: 'PERMISSION_DENIED',
+			id: '1370e5b7-d4eb-4566-bb1d-7748ee6a1838',
+		});
 	}
 
 	if (ep.meta.requireCredential && ep.meta.limit) {
@@ -41,24 +62,31 @@ export default async (endpoint: string, user: IUser, app: IApp, data: any, file?
 			await limiter(ep, user); // Rate limit
 		} catch (e) {
 			// drop request if limit exceeded
-			throw 'RATE_LIMIT_EXCEEDED';
+			throw new ApiError({
+				message: 'Rate limit exceeded. Please try again later.',
+				code: 'RATE_LIMIT_EXCEEDED',
+				id: 'd5826d14-3982-4d2e-8011-b9e9f02499ef',
+			});
 		}
 	}
 
-	let res;
+	let res: Response;
 
 	// API invoking
 	try {
 		res = await ep.exec(data, user, app, file);
 	} catch (e) {
-		if (e && e.name == 'INVALID_PARAM') {
-			throw {
-				code: e.name,
-				param: e.param,
-				reason: e.message
-			};
-		} else {
+		if (e instanceof ApiError) {
 			throw e;
+		} else {
+			apiLogger.error(e);
+			throw new ApiError(null, {
+				e: {
+					message: e.message,
+					code: e.code,
+					stack: e.stack
+				}
+			});
 		}
 	}
 
diff --git a/src/server/api/common/getters.ts b/src/server/api/common/getters.ts
index 1cd054cab1..f74f6130cb 100644
--- a/src/server/api/common/getters.ts
+++ b/src/server/api/common/getters.ts
@@ -1,6 +1,7 @@
 import * as mongo from 'mongodb';
-import Note from "../../../models/note";
-import User, { isRemoteUser, isLocalUser } from "../../../models/user";
+import Note from '../../../models/note';
+import User, { isRemoteUser, isLocalUser } from '../../../models/user';
+import { IdentifiableError } from '../../../misc/identifiable-error';
 
 /**
  * Get valied note for API processing
@@ -12,7 +13,7 @@ export async function getValiedNote(noteId: mongo.ObjectID) {
 	});
 
 	if (note === null) {
-		throw 'note not found';
+		throw new IdentifiableError('9725d0ce-ba28-4dde-95a7-2cbb2c15de24', 'No such note.');
 	}
 
 	return note;
@@ -27,7 +28,7 @@ export async function getUser(userId: mongo.ObjectID) {
 	});
 
 	if (user == null) {
-		throw 'user not found';
+		throw new IdentifiableError('15348ddd-432d-49c2-8a5a-8069753becff', 'No such user.');
 	}
 
 	return user;
diff --git a/src/server/api/define.ts b/src/server/api/define.ts
index de9a8caf96..f2fababc32 100644
--- a/src/server/api/define.ts
+++ b/src/server/api/define.ts
@@ -2,6 +2,7 @@ import * as fs from 'fs';
 import { ILocalUser } from '../../models/user';
 import { IApp } from '../../models/app';
 import { IEndpointMeta } from './endpoints';
+import { ApiError } from './error';
 
 type Params<T extends IEndpointMeta> = {
 	[P in keyof T['params']]: T['params'][P]['transform'] extends Function
@@ -9,13 +10,19 @@ type Params<T extends IEndpointMeta> = {
 		: ReturnType<T['params'][P]['validator']['get']>[0];
 };
 
-export default function <T extends IEndpointMeta>(meta: T, cb: (params: Params<T>, user: ILocalUser, app: IApp, file?: any, cleanup?: Function) => Promise<any>): (params: any, user: ILocalUser, app: IApp, file?: any) => Promise<any> {
+export type Response = Record<string, any> | void;
+
+export default function <T extends IEndpointMeta>(meta: T, cb: (params: Params<T>, user: ILocalUser, app: IApp, file?: any, cleanup?: Function) => Promise<Response>): (params: any, user: ILocalUser, app: IApp, file?: any) => Promise<any> {
 	return (params: any, user: ILocalUser, app: IApp, file?: any) => {
 		function cleanup() {
 			fs.unlink(file.path, () => {});
 		}
 
-		if (meta.requireFile && file == null) return Promise.reject('file required');
+		if (meta.requireFile && file == null) return Promise.reject(new ApiError({
+			message: 'File required.',
+			code: 'FILE_REQUIRED',
+			id: '4267801e-70d1-416a-b011-4ee502885d8b',
+		}));
 
 		const [ps, pserr] = getParams(meta, params);
 		if (pserr) {
@@ -27,17 +34,22 @@ export default function <T extends IEndpointMeta>(meta: T, cb: (params: Params<T
 	};
 }
 
-function getParams<T extends IEndpointMeta>(defs: T, params: any): [Params<T>, Error] {
+function getParams<T extends IEndpointMeta>(defs: T, params: any): [Params<T>, ApiError] {
 	if (defs.params == null) return [params, null];
 
 	const x: any = {};
-	let err: Error = null;
+	let err: ApiError = null;
 	Object.entries(defs.params).some(([k, def]) => {
 		const [v, e] = def.validator.get(params[k]);
 		if (e) {
-			err = new Error(e.message);
-			err.name = 'INVALID_PARAM';
-			(err as any).param = k;
+			err = new ApiError({
+				message: 'Invalid param.',
+				code: 'INVALID_PARAM',
+				id: '3d81ceae-475f-4600-b2a8-2bc116157532',
+			}, {
+				param: k,
+				reason: e.message
+			});
 			return true;
 		} else {
 			if (v === undefined && def.hasOwnProperty('default')) {
diff --git a/src/server/api/endpoints/admin/abuse-user-reports.ts b/src/server/api/endpoints/admin/abuse-user-reports.ts
index fc95dd4bb1..602171abb8 100644
--- a/src/server/api/endpoints/admin/abuse-user-reports.ts
+++ b/src/server/api/endpoints/admin/abuse-user-reports.ts
@@ -25,11 +25,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps) => {
 	const sort = {
 		_id: -1
 	};
@@ -51,5 +47,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await packMany(reports));
-}));
+	return await packMany(reports);
+});
diff --git a/src/server/api/endpoints/admin/drive/files.ts b/src/server/api/endpoints/admin/drive/files.ts
index 3a837e4189..318b2de1b2 100644
--- a/src/server/api/endpoints/admin/drive/files.ts
+++ b/src/server/api/endpoints/admin/drive/files.ts
@@ -46,7 +46,7 @@ const sort: any = { // < https://github.com/Microsoft/TypeScript/issues/1863
 	[fallback]: { _id: -1 }
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const q = {
 		'metadata.deletedAt': { $exists: false },
 	} as any;
@@ -61,5 +61,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			skip: ps.offset
 		});
 
-	res(await packMany(files, { detail: true, withUser: true, self: true }));
-}));
+	return await packMany(files, { detail: true, withUser: true, self: true });
+});
diff --git a/src/server/api/endpoints/admin/drive/show-file.ts b/src/server/api/endpoints/admin/drive/show-file.ts
index 6dfab19643..9b993584eb 100644
--- a/src/server/api/endpoints/admin/drive/show-file.ts
+++ b/src/server/api/endpoints/admin/drive/show-file.ts
@@ -2,6 +2,7 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
 import define from '../../../define';
 import DriveFile from '../../../../../models/drive-file';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	requireCredential: true,
@@ -12,17 +13,25 @@ export const meta = {
 			validator: $.type(ID),
 			transform: transform,
 		},
+	},
+
+	errors: {
+		noSuchFile: {
+			message: 'No such file.',
+			code: 'NO_SUCH_FILE',
+			id: 'caf3ca38-c6e5-472e-a30c-b05377dcc240'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const file = await DriveFile.findOne({
 		_id: ps.fileId
 	});
 
 	if (file == null) {
-		return rej('file not found');
+		throw new ApiError(meta.errors.noSuchFile);
 	}
 
-	res(file);
-}));
+	return file;
+});
diff --git a/src/server/api/endpoints/admin/emoji/add.ts b/src/server/api/endpoints/admin/emoji/add.ts
index cab3841649..b84e9d34d6 100644
--- a/src/server/api/endpoints/admin/emoji/add.ts
+++ b/src/server/api/endpoints/admin/emoji/add.ts
@@ -26,7 +26,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const emoji = await Emoji.insert({
 		updatedAt: new Date(),
 		name: ps.name,
@@ -35,7 +35,7 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		url: ps.url
 	});
 
-	res({
+	return {
 		id: emoji._id
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/admin/emoji/list.ts b/src/server/api/endpoints/admin/emoji/list.ts
index 624fa7845c..f51a536fab 100644
--- a/src/server/api/endpoints/admin/emoji/list.ts
+++ b/src/server/api/endpoints/admin/emoji/list.ts
@@ -18,16 +18,16 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const emojis = await Emoji.find({
 		host: ps.host
 	});
 
-	res(emojis.map(e => ({
+	return emojis.map(e => ({
 		id: e._id,
 		name: e.name,
 		aliases: e.aliases,
 		host: e.host,
 		url: e.url
-	})));
-}));
+	}));
+});
diff --git a/src/server/api/endpoints/admin/emoji/remove.ts b/src/server/api/endpoints/admin/emoji/remove.ts
index 1d6ed11b63..9699a00121 100644
--- a/src/server/api/endpoints/admin/emoji/remove.ts
+++ b/src/server/api/endpoints/admin/emoji/remove.ts
@@ -18,14 +18,14 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const emoji = await Emoji.findOne({
 		_id: ps.id
 	});
 
-	if (emoji == null) return rej('emoji not found');
+	if (emoji == null) throw new Error('emoji not found');
 
 	await Emoji.remove({ _id: emoji._id });
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/emoji/update.ts b/src/server/api/endpoints/admin/emoji/update.ts
index cbcc07fd48..7d065eaddb 100644
--- a/src/server/api/endpoints/admin/emoji/update.ts
+++ b/src/server/api/endpoints/admin/emoji/update.ts
@@ -30,12 +30,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const emoji = await Emoji.findOne({
 		_id: ps.id
 	});
 
-	if (emoji == null) return rej('emoji not found');
+	if (emoji == null) throw new Error('emoji not found');
 
 	await Emoji.update({ _id: emoji._id }, {
 		$set: {
@@ -46,5 +46,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/federation/remove-all-following.ts b/src/server/api/endpoints/admin/federation/remove-all-following.ts
index 8daff139b2..1a272aeb05 100644
--- a/src/server/api/endpoints/admin/federation/remove-all-following.ts
+++ b/src/server/api/endpoints/admin/federation/remove-all-following.ts
@@ -15,7 +15,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const followings = await Following.find({
 		'_follower.host': ps.host
 	});
@@ -29,5 +29,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		deleteFollowing(pair[0], pair[1]);
 	}
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/federation/update-instance.ts b/src/server/api/endpoints/admin/federation/update-instance.ts
index 579b437aa1..50eb4ba135 100644
--- a/src/server/api/endpoints/admin/federation/update-instance.ts
+++ b/src/server/api/endpoints/admin/federation/update-instance.ts
@@ -21,11 +21,11 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const instance = await Instance.findOne({ host: ps.host });
 
 	if (instance == null) {
-		return rej('instance not found');
+		throw new Error('instance not found');
 	}
 
 	Instance.update({ host: ps.host }, {
@@ -35,5 +35,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/invite.ts b/src/server/api/endpoints/admin/invite.ts
index ebfcb84452..3c2b323498 100644
--- a/src/server/api/endpoints/admin/invite.ts
+++ b/src/server/api/endpoints/admin/invite.ts
@@ -13,7 +13,7 @@ export const meta = {
 	params: {}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const code = rndstr({ length: 5, chars: '0-9' });
 
 	await RegistrationTicket.insert({
@@ -21,7 +21,7 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		code: code
 	});
 
-	res({
+	return {
 		code: code
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/admin/moderators/add.ts b/src/server/api/endpoints/admin/moderators/add.ts
index 4b4675c566..58515381d0 100644
--- a/src/server/api/endpoints/admin/moderators/add.ts
+++ b/src/server/api/endpoints/admin/moderators/add.ts
@@ -24,13 +24,13 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	await User.update({
@@ -41,5 +41,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/moderators/remove.ts b/src/server/api/endpoints/admin/moderators/remove.ts
index 2b9da61bb5..75627fb631 100644
--- a/src/server/api/endpoints/admin/moderators/remove.ts
+++ b/src/server/api/endpoints/admin/moderators/remove.ts
@@ -24,13 +24,13 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	await User.update({
@@ -41,5 +41,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/queue/clear.ts b/src/server/api/endpoints/admin/queue/clear.ts
index 4da8d2c72d..9a1e565955 100644
--- a/src/server/api/endpoints/admin/queue/clear.ts
+++ b/src/server/api/endpoints/admin/queue/clear.ts
@@ -8,8 +8,8 @@ export const meta = {
 	params: {}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	destroy();
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/remove-abuse-user-report.ts b/src/server/api/endpoints/admin/remove-abuse-user-report.ts
index 4d068a410e..c0c40c85da 100644
--- a/src/server/api/endpoints/admin/remove-abuse-user-report.ts
+++ b/src/server/api/endpoints/admin/remove-abuse-user-report.ts
@@ -15,18 +15,18 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const report = await AbuseUserReport.findOne({
 		_id: ps.reportId
 	});
 
 	if (report == null) {
-		return rej('report not found');
+		throw new Error('report not found');
 	}
 
 	await AbuseUserReport.remove({
 		_id: report._id
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/reset-password.ts b/src/server/api/endpoints/admin/reset-password.ts
index c072c12e0d..b274dc2a7d 100644
--- a/src/server/api/endpoints/admin/reset-password.ts
+++ b/src/server/api/endpoints/admin/reset-password.ts
@@ -25,17 +25,17 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	if (user.isAdmin) {
-		return rej('cannot reset password of admin');
+		throw new Error('cannot reset password of admin');
 	}
 
 	const passwd = rndstr('a-zA-Z0-9', 8);
@@ -46,12 +46,12 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 	await User.findOneAndUpdate({
 		_id: user._id
 	}, {
-			$set: {
-				password: hash
-			}
-		});
-
-	res({
-		password: passwd
+		$set: {
+			password: hash
+		}
 	});
-}));
+
+	return {
+		password: passwd
+	};
+});
diff --git a/src/server/api/endpoints/admin/show-user.ts b/src/server/api/endpoints/admin/show-user.ts
index 490b685352..5fcf4c3867 100644
--- a/src/server/api/endpoints/admin/show-user.ts
+++ b/src/server/api/endpoints/admin/show-user.ts
@@ -23,18 +23,18 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	if (me.isModerator && user.isAdmin) {
-		return rej('cannot show info of admin');
+		throw new Error('cannot show info of admin');
 	}
 
-	res(user);
-}));
+	return user;
+});
diff --git a/src/server/api/endpoints/admin/show-users.ts b/src/server/api/endpoints/admin/show-users.ts
index 3646f96d7d..9d1c5ea986 100644
--- a/src/server/api/endpoints/admin/show-users.ts
+++ b/src/server/api/endpoints/admin/show-users.ts
@@ -63,7 +63,7 @@ const sort: any = { // < https://github.com/Microsoft/TypeScript/issues/1863
 	[fallback]: { _id: -1 }
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const q = {
 		$and: []
 	} as any;
@@ -99,5 +99,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			skip: ps.offset
 		});
 
-	res(await Promise.all(users.map(user => pack(user, me, { detail: true }))));
-}));
+	return await Promise.all(users.map(user => pack(user, me, { detail: true })));
+});
diff --git a/src/server/api/endpoints/admin/silence-user.ts b/src/server/api/endpoints/admin/silence-user.ts
index 7b1090a895..532025563f 100644
--- a/src/server/api/endpoints/admin/silence-user.ts
+++ b/src/server/api/endpoints/admin/silence-user.ts
@@ -24,17 +24,17 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	if (user.isAdmin) {
-		return rej('cannot silence admin');
+		throw new Error('cannot silence admin');
 	}
 
 	await User.findOneAndUpdate({
@@ -45,5 +45,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/suspend-user.ts b/src/server/api/endpoints/admin/suspend-user.ts
index 2ec5196880..321c3955e6 100644
--- a/src/server/api/endpoints/admin/suspend-user.ts
+++ b/src/server/api/endpoints/admin/suspend-user.ts
@@ -24,30 +24,30 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	if (user.isAdmin) {
-		return rej('cannot suspend admin');
+		throw new Error('cannot suspend admin');
 	}
 
 	if (user.isModerator) {
-		return rej('cannot suspend moderator');
+		throw new Error('cannot suspend moderator');
 	}
 
 	await User.findOneAndUpdate({
 		_id: user._id
 	}, {
-			$set: {
-				isSuspended: true
-			}
-		});
+		$set: {
+			isSuspended: true
+		}
+	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/unsilence-user.ts b/src/server/api/endpoints/admin/unsilence-user.ts
index a01bfbb6d2..bb039eb8da 100644
--- a/src/server/api/endpoints/admin/unsilence-user.ts
+++ b/src/server/api/endpoints/admin/unsilence-user.ts
@@ -24,13 +24,13 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	await User.findOneAndUpdate({
@@ -41,5 +41,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/unsuspend-user.ts b/src/server/api/endpoints/admin/unsuspend-user.ts
index 4b53246264..4732e44369 100644
--- a/src/server/api/endpoints/admin/unsuspend-user.ts
+++ b/src/server/api/endpoints/admin/unsuspend-user.ts
@@ -24,22 +24,22 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	await User.findOneAndUpdate({
 		_id: user._id
 	}, {
-			$set: {
-				isSuspended: false
-			}
-		});
+		$set: {
+			isSuspended: false
+		}
+	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/unverify-user.ts b/src/server/api/endpoints/admin/unverify-user.ts
index 3e044ffed7..857cceb1ec 100644
--- a/src/server/api/endpoints/admin/unverify-user.ts
+++ b/src/server/api/endpoints/admin/unverify-user.ts
@@ -24,22 +24,22 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	await User.findOneAndUpdate({
 		_id: user._id
 	}, {
-			$set: {
-				isVerified: false
-			}
-		});
+		$set: {
+			isVerified: false
+		}
+	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/update-meta.ts b/src/server/api/endpoints/admin/update-meta.ts
index da2ee36927..1fb87d0a98 100644
--- a/src/server/api/endpoints/admin/update-meta.ts
+++ b/src/server/api/endpoints/admin/update-meta.ts
@@ -323,7 +323,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const set = {} as any;
 
 	if (ps.broadcasts) {
@@ -506,5 +506,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		$set: set
 	}, { upsert: true });
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/admin/update-remote-user.ts b/src/server/api/endpoints/admin/update-remote-user.ts
index 9288ce1fb7..8d1db33ba4 100644
--- a/src/server/api/endpoints/admin/update-remote-user.ts
+++ b/src/server/api/endpoints/admin/update-remote-user.ts
@@ -26,9 +26,10 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise((res, rej) => {
-	updatePersonById(ps.userId).then(() => res(), e => rej(e));
-}));
+export default define(meta, async (ps) => {
+	await updatePersonById(ps.userId);
+	return;
+});
 
 async function updatePersonById(userId: mongo.ObjectID) {
 	const user = await getRemoteUser(userId);
diff --git a/src/server/api/endpoints/admin/verify-user.ts b/src/server/api/endpoints/admin/verify-user.ts
index 996e044d18..77db8e6e60 100644
--- a/src/server/api/endpoints/admin/verify-user.ts
+++ b/src/server/api/endpoints/admin/verify-user.ts
@@ -24,22 +24,22 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new Error('user not found');
 	}
 
 	await User.findOneAndUpdate({
 		_id: user._id
 	}, {
-			$set: {
-				isVerified: true
-			}
-		});
+		$set: {
+			isVerified: true
+		}
+	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/aggregation/hashtags.ts b/src/server/api/endpoints/aggregation/hashtags.ts
index 99ef8901db..6de36a1d1a 100644
--- a/src/server/api/endpoints/aggregation/hashtags.ts
+++ b/src/server/api/endpoints/aggregation/hashtags.ts
@@ -6,7 +6,7 @@ export const meta = {
 	requireCredential: false,
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const instance = await fetchMeta();
 	const hidedTags = instance.hidedTags.map(t => t.toLowerCase());
 
@@ -40,7 +40,7 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 	//#endregion
 
 	if (data.length == 0) {
-		return res([]);
+		return [];
 	}
 
 	let tags: {
@@ -66,5 +66,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 
 	tags = tags.slice(0, 30);
 
-	res(tags);
-}));
+	return tags;
+});
diff --git a/src/server/api/endpoints/ap/show.ts b/src/server/api/endpoints/ap/show.ts
index 3b4021e0a7..8dd9f96f90 100644
--- a/src/server/api/endpoints/ap/show.ts
+++ b/src/server/api/endpoints/ap/show.ts
@@ -7,6 +7,7 @@ import { createPerson } from '../../../../remote/activitypub/models/person';
 import Note, { pack as packNote, INote } from '../../../../models/note';
 import { createNote } from '../../../../remote/activitypub/models/note';
 import Resolver from '../../../../remote/activitypub/resolver';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -23,13 +24,24 @@ export const meta = {
 			}
 		},
 	},
+
+	errors: {
+		noSuchObject: {
+			message: 'No such object.',
+			code: 'NO_SUCH_OBJECT',
+			id: 'dc94d745-1262-4e63-a17d-fecaa57efc82'
+		}
+	}
 };
 
-export default define(meta, (ps) => new Promise((res, rej) => {
-	fetchAny(ps.uri)
-		.then(object => object != null ? res(object) : rej('object not found'))
-		.catch(e => rej(e));
-}));
+export default define(meta, async (ps) => {
+	const object = await fetchAny(ps.uri);
+	if (object) {
+		return object;
+	} else {
+		throw new ApiError(meta.errors.noSuchObject);
+	}
+});
 
 /***
  * URIからUserかNoteを解決する
diff --git a/src/server/api/endpoints/app/create.ts b/src/server/api/endpoints/app/create.ts
index 849530c20d..ef8bd66076 100644
--- a/src/server/api/endpoints/app/create.ts
+++ b/src/server/api/endpoints/app/create.ts
@@ -27,7 +27,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Generate secret
 	const secret = rndstr('a-zA-Z0-9', 32);
 
@@ -42,9 +42,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		secret: secret
 	});
 
-	// Response
-	res(await pack(app, null, {
+	return await pack(app, null, {
 		detail: true,
 		includeSecret: true
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/app/show.ts b/src/server/api/endpoints/app/show.ts
index cb47b40abf..72755ce01d 100644
--- a/src/server/api/endpoints/app/show.ts
+++ b/src/server/api/endpoints/app/show.ts
@@ -2,6 +2,7 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../misc/cafy-id';
 import App, { pack } from '../../../../models/app';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	params: {
@@ -9,22 +10,29 @@ export const meta = {
 			validator: $.type(ID),
 			transform: transform
 		},
+	},
+
+	errors: {
+		noSuchApp: {
+			message: 'No such app.',
+			code: 'NO_SUCH_APP',
+			id: 'dce83913-2dc6-4093-8a7b-71dbb11718a3'
+		}
 	}
 };
 
-export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user, app) => {
 	const isSecure = user != null && app == null;
 
 	// Lookup app
 	const ap = await App.findOne({ _id: ps.appId });
 
 	if (ap === null) {
-		return rej('app not found');
+		throw new ApiError(meta.errors.noSuchApp);
 	}
 
-	// Send response
-	res(await pack(ap, user, {
+	return await pack(ap, user, {
 		detail: true,
 		includeSecret: isSecure && ap.userId.equals(user._id)
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/auth/accept.ts b/src/server/api/endpoints/auth/accept.ts
index 3e45a2801f..964ee6559f 100644
--- a/src/server/api/endpoints/auth/accept.ts
+++ b/src/server/api/endpoints/auth/accept.ts
@@ -5,6 +5,7 @@ import App from '../../../../models/app';
 import AuthSess from '../../../../models/auth-session';
 import AccessToken from '../../../../models/access-token';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	requireCredential: true,
@@ -15,16 +16,24 @@ export const meta = {
 		token: {
 			validator: $.str
 		}
+	},
+
+	errors: {
+		noSuchSession: {
+			message: 'No such session.',
+			code: 'NO_SUCH_SESSION',
+			id: '9c72d8de-391a-43c1-9d06-08d29efde8df'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch token
 	const session = await AuthSess
 		.findOne({ token: ps.token });
 
 	if (session === null) {
-		return rej('session not found');
+		throw new ApiError(meta.errors.noSuchSession);
 	}
 
 	// Generate access token
@@ -64,6 +73,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	// Response
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/auth/session/generate.ts b/src/server/api/endpoints/auth/session/generate.ts
index 5ef3404b73..9f0f184719 100644
--- a/src/server/api/endpoints/auth/session/generate.ts
+++ b/src/server/api/endpoints/auth/session/generate.ts
@@ -4,6 +4,7 @@ import App from '../../../../../models/app';
 import AuthSess from '../../../../../models/auth-session';
 import config from '../../../../../config';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	requireCredential: false,
@@ -12,17 +13,25 @@ export const meta = {
 		appSecret: {
 			validator: $.str
 		}
+	},
+
+	errors: {
+		noSuchApp: {
+			message: 'No such app.',
+			code: 'NO_SUCH_APP',
+			id: '92f93e63-428e-4f2f-a5a4-39e1407fe998'
+		}
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	// Lookup app
 	const app = await App.findOne({
 		secret: ps.appSecret
 	});
 
 	if (app == null) {
-		return rej('app not found');
+		throw new ApiError(meta.errors.noSuchApp);
 	}
 
 	// Generate token
@@ -35,9 +44,8 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		token: token
 	});
 
-	// Response
-	res({
+	return {
 		token: doc.token,
 		url: `${config.auth_url}/${doc.token}`
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/auth/session/show.ts b/src/server/api/endpoints/auth/session/show.ts
index cc63c43ad3..5e9e68c2c4 100644
--- a/src/server/api/endpoints/auth/session/show.ts
+++ b/src/server/api/endpoints/auth/session/show.ts
@@ -1,6 +1,7 @@
 import $ from 'cafy';
 import AuthSess, { pack } from '../../../../../models/auth-session';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	requireCredential: false,
@@ -9,19 +10,26 @@ export const meta = {
 		token: {
 			validator: $.str
 		}
+	},
+
+	errors: {
+		noSuchSession: {
+			message: 'No such session.',
+			code: 'NO_SUCH_SESSION',
+			id: 'bd72c97d-eba7-4adb-a467-f171b8847250'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Lookup session
 	const session = await AuthSess.findOne({
 		token: ps.token
 	});
 
 	if (session == null) {
-		return rej('session not found');
+		throw new ApiError(meta.errors.noSuchSession);
 	}
 
-	// Response
-	res(await pack(session, user));
-}));
+	return await pack(session, user);
+});
diff --git a/src/server/api/endpoints/auth/session/userkey.ts b/src/server/api/endpoints/auth/session/userkey.ts
index 9f924d27a0..17d62886a5 100644
--- a/src/server/api/endpoints/auth/session/userkey.ts
+++ b/src/server/api/endpoints/auth/session/userkey.ts
@@ -4,6 +4,7 @@ import AuthSess from '../../../../../models/auth-session';
 import AccessToken from '../../../../../models/access-token';
 import { pack } from '../../../../../models/user';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	requireCredential: false,
@@ -16,17 +17,37 @@ export const meta = {
 		token: {
 			validator: $.str
 		}
+	},
+
+	errors: {
+		noSuchApp: {
+			message: 'No such app.',
+			code: 'NO_SUCH_APP',
+			id: 'fcab192a-2c5a-43b7-8ad8-9b7054d8d40d'
+		},
+
+		noSuchSession: {
+			message: 'No such session.',
+			code: 'NO_SUCH_SESSION',
+			id: '5b5a1503-8bc8-4bd0-8054-dc189e8cdcb3'
+		},
+
+		pendingSession: {
+			message: 'This session is not completed yet.',
+			code: 'PENDING_SESSION',
+			id: '8c8a4145-02cc-4cca-8e66-29ba60445a8e'
+		}
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	// Lookup app
 	const app = await App.findOne({
 		secret: ps.appSecret
 	});
 
 	if (app == null) {
-		return rej('app not found');
+		throw new ApiError(meta.errors.noSuchApp);
 	}
 
 	// Fetch token
@@ -37,11 +58,11 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		});
 
 	if (session === null) {
-		return rej('session not found');
+		throw new ApiError(meta.errors.noSuchSession);
 	}
 
 	if (session.userId == null) {
-		return rej('this session is not allowed yet');
+		throw new ApiError(meta.errors.pendingSession);
 	}
 
 	// Lookup access token
@@ -61,11 +82,10 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 		_id: session._id
 	});
 
-	// Response
-	res({
+	return {
 		accessToken: accessToken.token,
 		user: await pack(session.userId, null, {
 			detail: true
 		})
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/blocking/create.ts b/src/server/api/endpoints/blocking/create.ts
index 6fa7efb558..7e15b2d7ff 100644
--- a/src/server/api/endpoints/blocking/create.ts
+++ b/src/server/api/endpoints/blocking/create.ts
@@ -5,6 +5,7 @@ import User, { pack } from '../../../../models/user';
 import Blocking from '../../../../models/blocking';
 import create from '../../../../services/blocking/create';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -32,15 +33,35 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '7cc4f851-e2f1-4621-9633-ec9e1d00c01e'
+		},
+
+		blockeeIsYourself: {
+			message: 'Blockee is yourself.',
+			code: 'BLOCKEE_IS_YOURSELF',
+			id: '88b19138-f28d-42c0-8499-6a31bbd0fdc6'
+		},
+
+		alreadyBlocking: {
+			message: 'You are already blocking that user.',
+			code: 'ALREADY_BLOCKING',
+			id: '787fed64-acb9-464a-82eb-afbd745b9614'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const blocker = user;
 
 	// 自分自身
 	if (user._id.equals(ps.userId)) {
-		return rej('blockee is yourself');
+		throw new ApiError(meta.errors.blockeeIsYourself);
 	}
 
 	// Get blockee
@@ -54,7 +75,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (blockee === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Check if already blocking
@@ -64,14 +85,13 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist !== null) {
-		return rej('already blocking');
+		throw new ApiError(meta.errors.alreadyBlocking);
 	}
 
 	// Create blocking
 	await create(blocker, blockee);
 
-	// Send response
-	res(await pack(blockee._id, user, {
+	return await pack(blockee._id, user, {
 		detail: true
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/blocking/delete.ts b/src/server/api/endpoints/blocking/delete.ts
index c176da1ea8..475f2c30a1 100644
--- a/src/server/api/endpoints/blocking/delete.ts
+++ b/src/server/api/endpoints/blocking/delete.ts
@@ -5,6 +5,7 @@ import User, { pack } from '../../../../models/user';
 import Blocking from '../../../../models/blocking';
 import deleteBlocking from '../../../../services/blocking/delete';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -32,15 +33,35 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '8621d8bf-c358-4303-a066-5ea78610eb3f'
+		},
+
+		blockeeIsYourself: {
+			message: 'Blockee is yourself.',
+			code: 'BLOCKEE_IS_YOURSELF',
+			id: '06f6fac6-524b-473c-a354-e97a40ae6eac'
+		},
+
+		notBlocking: {
+			message: 'You are not blocking that user.',
+			code: 'NOT_BLOCKING',
+			id: '291b2efa-60c6-45c0-9f6a-045c8f9b02cd'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const blocker = user;
 
 	// Check if the blockee is yourself
 	if (user._id.equals(ps.userId)) {
-		return rej('blockee is yourself');
+		throw new ApiError(meta.errors.blockeeIsYourself);
 	}
 
 	// Get blockee
@@ -54,7 +75,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (blockee === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Check not blocking
@@ -64,14 +85,13 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist === null) {
-		return rej('already not blocking');
+		throw new ApiError(meta.errors.notBlocking);
 	}
 
 	// Delete blocking
 	await deleteBlocking(blocker, blockee);
 
-	// Send response
-	res(await pack(blockee._id, user, {
+	return await pack(blockee._id, user, {
 		detail: true
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/blocking/list.ts b/src/server/api/endpoints/blocking/list.ts
index 79eaaece8a..088b2c488a 100644
--- a/src/server/api/endpoints/blocking/list.ts
+++ b/src/server/api/endpoints/blocking/list.ts
@@ -31,12 +31,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, me) => {
 	const query = {
 		blockerId: me._id
 	} as any;
@@ -62,5 +57,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await packMany(blockings, me));
-}));
+	return await packMany(blockings, me);
+});
diff --git a/src/server/api/endpoints/charts/active-users.ts b/src/server/api/endpoints/charts/active-users.ts
index 9adf7bd388..11f86d0baa 100644
--- a/src/server/api/endpoints/charts/active-users.ts
+++ b/src/server/api/endpoints/charts/active-users.ts
@@ -27,8 +27,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await activeUsersChart.getChart(ps.span as any, ps.limit);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await activeUsersChart.getChart(ps.span as any, ps.limit);
+});
diff --git a/src/server/api/endpoints/charts/drive.ts b/src/server/api/endpoints/charts/drive.ts
index 0f1106e123..9244ef7481 100644
--- a/src/server/api/endpoints/charts/drive.ts
+++ b/src/server/api/endpoints/charts/drive.ts
@@ -27,8 +27,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await driveChart.getChart(ps.span as any, ps.limit);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await driveChart.getChart(ps.span as any, ps.limit);
+});
diff --git a/src/server/api/endpoints/charts/federation.ts b/src/server/api/endpoints/charts/federation.ts
index 6b9cfc4510..c98c9f6cbb 100644
--- a/src/server/api/endpoints/charts/federation.ts
+++ b/src/server/api/endpoints/charts/federation.ts
@@ -27,8 +27,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await federationChart.getChart(ps.span as any, ps.limit);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await federationChart.getChart(ps.span as any, ps.limit);
+});
diff --git a/src/server/api/endpoints/charts/hashtag.ts b/src/server/api/endpoints/charts/hashtag.ts
index e1127fe388..5905fdc1a2 100644
--- a/src/server/api/endpoints/charts/hashtag.ts
+++ b/src/server/api/endpoints/charts/hashtag.ts
@@ -34,8 +34,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await hashtagChart.getChart(ps.span as any, ps.limit, ps.tag);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await hashtagChart.getChart(ps.span as any, ps.limit, ps.tag);
+});
diff --git a/src/server/api/endpoints/charts/instance.ts b/src/server/api/endpoints/charts/instance.ts
index 9b5f33024a..e47334c7ce 100644
--- a/src/server/api/endpoints/charts/instance.ts
+++ b/src/server/api/endpoints/charts/instance.ts
@@ -35,8 +35,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await instanceChart.getChart(ps.span as any, ps.limit, ps.host);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await instanceChart.getChart(ps.span as any, ps.limit, ps.host);
+});
diff --git a/src/server/api/endpoints/charts/network.ts b/src/server/api/endpoints/charts/network.ts
index db13f13030..fa1917f753 100644
--- a/src/server/api/endpoints/charts/network.ts
+++ b/src/server/api/endpoints/charts/network.ts
@@ -27,8 +27,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await networkChart.getChart(ps.span as any, ps.limit);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await networkChart.getChart(ps.span as any, ps.limit);
+});
diff --git a/src/server/api/endpoints/charts/notes.ts b/src/server/api/endpoints/charts/notes.ts
index 4877df6080..006a8d6e21 100644
--- a/src/server/api/endpoints/charts/notes.ts
+++ b/src/server/api/endpoints/charts/notes.ts
@@ -27,8 +27,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await notesChart.getChart(ps.span as any, ps.limit);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await notesChart.getChart(ps.span as any, ps.limit);
+});
diff --git a/src/server/api/endpoints/charts/user/drive.ts b/src/server/api/endpoints/charts/user/drive.ts
index 556651d335..6383ddf2f8 100644
--- a/src/server/api/endpoints/charts/user/drive.ts
+++ b/src/server/api/endpoints/charts/user/drive.ts
@@ -37,8 +37,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await perUserDriveChart.getChart(ps.span as any, ps.limit, ps.userId);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await perUserDriveChart.getChart(ps.span as any, ps.limit, ps.userId);
+});
diff --git a/src/server/api/endpoints/charts/user/following.ts b/src/server/api/endpoints/charts/user/following.ts
index ccc83952f3..9443b56a40 100644
--- a/src/server/api/endpoints/charts/user/following.ts
+++ b/src/server/api/endpoints/charts/user/following.ts
@@ -37,8 +37,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await perUserFollowingChart.getChart(ps.span as any, ps.limit, ps.userId);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return  await perUserFollowingChart.getChart(ps.span as any, ps.limit, ps.userId);
+});
diff --git a/src/server/api/endpoints/charts/user/notes.ts b/src/server/api/endpoints/charts/user/notes.ts
index 3296771c68..da642fc761 100644
--- a/src/server/api/endpoints/charts/user/notes.ts
+++ b/src/server/api/endpoints/charts/user/notes.ts
@@ -37,8 +37,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await perUserNotesChart.getChart(ps.span as any, ps.limit, ps.userId);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await perUserNotesChart.getChart(ps.span as any, ps.limit, ps.userId);
+});
diff --git a/src/server/api/endpoints/charts/user/reactions.ts b/src/server/api/endpoints/charts/user/reactions.ts
index be228b5f7d..e440b3ae34 100644
--- a/src/server/api/endpoints/charts/user/reactions.ts
+++ b/src/server/api/endpoints/charts/user/reactions.ts
@@ -37,8 +37,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await perUserReactionsChart.getChart(ps.span as any, ps.limit, ps.userId);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await perUserReactionsChart.getChart(ps.span as any, ps.limit, ps.userId);
+});
diff --git a/src/server/api/endpoints/charts/users.ts b/src/server/api/endpoints/charts/users.ts
index e474e29970..ea32b7afd8 100644
--- a/src/server/api/endpoints/charts/users.ts
+++ b/src/server/api/endpoints/charts/users.ts
@@ -27,8 +27,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	const stats = await usersChart.getChart(ps.span as any, ps.limit);
-
-	res(stats);
-}));
+export default define(meta, async (ps) => {
+	return await usersChart.getChart(ps.span as any, ps.limit);
+});
diff --git a/src/server/api/endpoints/drive.ts b/src/server/api/endpoints/drive.ts
index 3480fe6002..54afe55cb9 100644
--- a/src/server/api/endpoints/drive.ts
+++ b/src/server/api/endpoints/drive.ts
@@ -13,35 +13,34 @@ export const meta = {
 	kind: 'drive-read'
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const instance = await fetchMeta();
 
 	// Calculate drive usage
-	const usage = await DriveFile
-		.aggregate([{
-			$match: {
-				'metadata.userId': user._id,
-				'metadata.deletedAt': { $exists: false }
-			}
-		}, {
-			$project: {
-				length: true
-			}
-		}, {
-			$group: {
-				_id: null,
-				usage: { $sum: '$length' }
-			}
-		}])
-		.then((aggregates: any[]) => {
-			if (aggregates.length > 0) {
-				return aggregates[0].usage;
-			}
-			return 0;
-		});
+	const usage = await DriveFile.aggregate([{
+		$match: {
+			'metadata.userId': user._id,
+			'metadata.deletedAt': { $exists: false }
+		}
+	}, {
+		$project: {
+			length: true
+		}
+	}, {
+		$group: {
+			_id: null,
+			usage: { $sum: '$length' }
+		}
+	}])
+	.then((aggregates: any[]) => {
+		if (aggregates.length > 0) {
+			return aggregates[0].usage;
+		}
+		return 0;
+	});
 
-	res({
+	return {
 		capacity: 1024 * 1024 * instance.localDriveCapacityMb,
 		usage: usage
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/drive/files.ts b/src/server/api/endpoints/drive/files.ts
index 6b96313910..1c12f0dc07 100644
--- a/src/server/api/endpoints/drive/files.ts
+++ b/src/server/api/endpoints/drive/files.ts
@@ -41,12 +41,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	const sort = {
 		_id: -1
 	};
@@ -78,5 +73,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await packMany(files, { detail: false, self: true }));
-}));
+	return await packMany(files, { detail: false, self: true });
+});
diff --git a/src/server/api/endpoints/drive/files/attached_notes.ts b/src/server/api/endpoints/drive/files/attached_notes.ts
index 6442b15195..506444b183 100644
--- a/src/server/api/endpoints/drive/files/attached_notes.ts
+++ b/src/server/api/endpoints/drive/files/attached_notes.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import DriveFile from '../../../../../models/drive-file';
 import define from '../../../define';
 import { packMany } from '../../../../../models/note';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -25,10 +26,18 @@ export const meta = {
 				'en-US': 'Target file ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFile: {
+			message: 'No such file.',
+			code: 'NO_SUCH_FILE',
+			id: 'c118ece3-2e4b-4296-99d1-51756e32d232',
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch file
 	const file = await DriveFile
 		.findOne({
@@ -38,10 +47,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 	if (file === null) {
-		return rej('file-not-found');
+		throw new ApiError(meta.errors.noSuchFile);
 	}
 
-	res(await packMany(file.metadata.attachedNoteIds || [], user, {
+	return await packMany(file.metadata.attachedNoteIds || [], user, {
 		detail: true
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/drive/files/check_existence.ts b/src/server/api/endpoints/drive/files/check_existence.ts
index 6e986d4170..aafd46fb2d 100644
--- a/src/server/api/endpoints/drive/files/check_existence.ts
+++ b/src/server/api/endpoints/drive/files/check_existence.ts
@@ -22,16 +22,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const file = await DriveFile.findOne({
 		md5: ps.md5,
 		'metadata.userId': user._id,
 		'metadata.deletedAt': { $exists: false }
 	});
 
-	if (file === null) {
-		res({ file: null });
-	} else {
-		res({ file: await pack(file, { self: true }) });
-	}
-}));
+	return { file: file ? await pack(file, { self: true }) : null };
+});
diff --git a/src/server/api/endpoints/drive/files/create.ts b/src/server/api/endpoints/drive/files/create.ts
index 3611652b6c..c96e4bbf19 100644
--- a/src/server/api/endpoints/drive/files/create.ts
+++ b/src/server/api/endpoints/drive/files/create.ts
@@ -5,6 +5,7 @@ import { validateFileName, pack } from '../../../../../models/drive-file';
 import create from '../../../../../services/drive/add-file';
 import define from '../../../define';
 import { apiLogger } from '../../../logger';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -51,10 +52,18 @@ export const meta = {
 				'ja-JP': 'true にすると、同じハッシュを持つファイルが既にアップロードされていても強制的にファイルを作成します。',
 			}
 		}
+	},
+
+	errors: {
+		invalidFileName: {
+			message: 'Invalid file name.',
+			code: 'INVALID_FILE_NAME',
+			id: 'f449b209-0c60-4e51-84d5-29486263bfd4'
+		}
 	}
 };
 
-export default define(meta, (ps, user, app, file, cleanup) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user, app, file, cleanup) => {
 	// Get 'name' parameter
 	let name = file.originalname;
 	if (name !== undefined && name !== null) {
@@ -64,7 +73,7 @@ export default define(meta, (ps, user, app, file, cleanup) => new Promise(async
 		} else if (name === 'blob') {
 			name = null;
 		} else if (!validateFileName(name)) {
-			return rej('invalid name');
+			throw new ApiError(meta.errors.invalidFileName);
 		}
 	} else {
 		name = null;
@@ -73,15 +82,11 @@ export default define(meta, (ps, user, app, file, cleanup) => new Promise(async
 	try {
 		// Create file
 		const driveFile = await create(user, file.path, name, null, ps.folderId, ps.force, false, null, null, ps.isSensitive);
-
-		cleanup();
-
-		res(pack(driveFile, { self: true }));
+		return pack(driveFile, { self: true });
 	} catch (e) {
 		apiLogger.error(e);
-
+		throw new ApiError();
+	} finally {
 		cleanup();
-
-		rej(e);
 	}
-}));
+});
diff --git a/src/server/api/endpoints/drive/files/delete.ts b/src/server/api/endpoints/drive/files/delete.ts
index c322587d8f..2dc493efeb 100644
--- a/src/server/api/endpoints/drive/files/delete.ts
+++ b/src/server/api/endpoints/drive/files/delete.ts
@@ -4,6 +4,7 @@ import DriveFile from '../../../../../models/drive-file';
 import del from '../../../../../services/drive/delete-file';
 import { publishDriveStream } from '../../../../../services/stream';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -26,10 +27,24 @@ export const meta = {
 				'en-US': 'Target file ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFile: {
+			message: 'No such file.',
+			code: 'NO_SUCH_FILE',
+			id: '908939ec-e52b-4458-b395-1025195cea58'
+		},
+
+		accessDenied: {
+			message: 'Access denied.',
+			code: 'ACCESS_DENIED',
+			id: '5eb8d909-2540-4970-90b8-dd6f86088121'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch file
 	const file = await DriveFile
 		.findOne({
@@ -37,11 +52,11 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 	if (file === null) {
-		return rej('file-not-found');
+		throw new ApiError(meta.errors.noSuchFile);
 	}
 
 	if (!user.isAdmin && !user.isModerator && !file.metadata.userId.equals(user._id)) {
-		return rej('access denied');
+		throw new ApiError(meta.errors.accessDenied);
 	}
 
 	// Delete
@@ -50,5 +65,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	// Publish fileDeleted event
 	publishDriveStream(user._id, 'fileDeleted', file._id);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/drive/files/find.ts b/src/server/api/endpoints/drive/files/find.ts
index 0ebd5b789e..6eb909b9d0 100644
--- a/src/server/api/endpoints/drive/files/find.ts
+++ b/src/server/api/endpoints/drive/files/find.ts
@@ -24,7 +24,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const files = await DriveFile
 		.find({
 			filename: ps.name,
@@ -32,5 +32,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			'metadata.folderId': ps.folderId
 		});
 
-	res(await Promise.all(files.map(file => pack(file, { self: true }))));
-}));
+	return await Promise.all(files.map(file => pack(file, { self: true })));
+});
diff --git a/src/server/api/endpoints/drive/files/show.ts b/src/server/api/endpoints/drive/files/show.ts
index 994583bd01..f844d434fe 100644
--- a/src/server/api/endpoints/drive/files/show.ts
+++ b/src/server/api/endpoints/drive/files/show.ts
@@ -4,6 +4,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import DriveFile, { pack, IDriveFile } from '../../../../../models/drive-file';
 import define from '../../../define';
 import config from '../../../../../config';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -34,10 +35,30 @@ export const meta = {
 				'en-US': 'Target file URL'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFile: {
+			message: 'No such file.',
+			code: 'NO_SUCH_FILE',
+			id: '067bc436-2718-4795-b0fb-ecbe43949e31'
+		},
+
+		accessDenied: {
+			message: 'Access denied.',
+			code: 'ACCESS_DENIED',
+			id: '25b73c73-68b1-41d0-bad1-381cfdf6579f'
+		},
+
+		fileIdOrUrlRequired: {
+			message: 'fileId or url required.',
+			code: 'INVALID_PARAM',
+			id: '89674805-722c-440c-8d88-5641830dc3e4'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	let file: IDriveFile;
 
 	if (ps.fileId) {
@@ -69,22 +90,19 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			});
 		}
 	} else {
-		return rej('fileId or url required');
+		throw new ApiError(meta.errors.fileIdOrUrlRequired);
 	}
 
 	if (!user.isAdmin && !user.isModerator && !file.metadata.userId.equals(user._id)) {
-		return rej('access denied');
+		throw new ApiError(meta.errors.accessDenied);
 	}
 
 	if (file === null) {
-		return rej('file-not-found');
+		throw new ApiError(meta.errors.noSuchFile);
 	}
 
-	// Serialize
-	const _file = await pack(file, {
+	return await pack(file, {
 		detail: true,
 		self: true
 	});
-
-	res(_file);
-}));
+});
diff --git a/src/server/api/endpoints/drive/files/update.ts b/src/server/api/endpoints/drive/files/update.ts
index 79acbec3cd..f24cc6bcd3 100644
--- a/src/server/api/endpoints/drive/files/update.ts
+++ b/src/server/api/endpoints/drive/files/update.ts
@@ -5,6 +5,7 @@ import DriveFile, { validateFileName, pack } from '../../../../../models/drive-f
 import { publishDriveStream } from '../../../../../services/stream';
 import define from '../../../define';
 import Note from '../../../../../models/note';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -51,10 +52,30 @@ export const meta = {
 				'en-US': 'Whether this media is NSFW'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFile: {
+			message: 'No such file.',
+			code: 'NO_SUCH_FILE',
+			id: 'e7778c7e-3af9-49cd-9690-6dbc3e6c972d'
+		},
+
+		accessDenied: {
+			message: 'Access denied.',
+			code: 'ACCESS_DENIED',
+			id: '01a53b27-82fc-445b-a0c1-b558465a8ed2'
+		},
+
+		noSuchFolder: {
+			message: 'No such folder.',
+			code: 'NO_SUCH_FOLDER',
+			id: 'ea8fb7a5-af77-4a08-b608-c0218176cd73'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch file
 	const file = await DriveFile
 		.findOne({
@@ -62,11 +83,11 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 	if (file === null) {
-		return rej('file-not-found');
+		throw new ApiError(meta.errors.noSuchFile);
 	}
 
 	if (!user.isAdmin && !user.isModerator && !file.metadata.userId.equals(user._id)) {
-		return rej('access denied');
+		throw new ApiError(meta.errors.accessDenied);
 	}
 
 	if (ps.name) file.filename = ps.name;
@@ -85,7 +106,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 				});
 
 			if (folder === null) {
-				return rej('folder-not-found');
+				throw new ApiError(meta.errors.noSuchFolder);
 			}
 
 			file.metadata.folderId = folder._id;
@@ -114,12 +135,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	// Serialize
 	const fileObj = await pack(file, { self: true });
 
-	// Response
-	res(fileObj);
-
 	// Publish fileUpdated event
 	publishDriveStream(user._id, 'fileUpdated', fileObj);
-}));
+
+	return fileObj;
+});
diff --git a/src/server/api/endpoints/drive/files/upload_from_url.ts b/src/server/api/endpoints/drive/files/upload_from_url.ts
index d79b321735..8d25530ddd 100644
--- a/src/server/api/endpoints/drive/files/upload_from_url.ts
+++ b/src/server/api/endpoints/drive/files/upload_from_url.ts
@@ -50,6 +50,6 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	res(pack(await uploadFromUrl(ps.url, user, ps.folderId, null, ps.isSensitive, ps.force), { self: true }));
-}));
+export default define(meta, async (ps, user) => {
+	return await pack(await uploadFromUrl(ps.url, user, ps.folderId, null, ps.isSensitive, ps.force), { self: true });
+});
diff --git a/src/server/api/endpoints/drive/folders.ts b/src/server/api/endpoints/drive/folders.ts
index bdbbf35ff1..6982060850 100644
--- a/src/server/api/endpoints/drive/folders.ts
+++ b/src/server/api/endpoints/drive/folders.ts
@@ -37,12 +37,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	const sort = {
 		_id: -1
 	};
@@ -67,5 +62,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await Promise.all(folders.map(folder => pack(folder))));
-}));
+	return await Promise.all(folders.map(folder => pack(folder)));
+});
diff --git a/src/server/api/endpoints/drive/folders/create.ts b/src/server/api/endpoints/drive/folders/create.ts
index f4b520be28..a54c780b8e 100644
--- a/src/server/api/endpoints/drive/folders/create.ts
+++ b/src/server/api/endpoints/drive/folders/create.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import DriveFolder, { isValidFolderName, pack } from '../../../../../models/drive-folder';
 import { publishDriveStream } from '../../../../../services/stream';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -34,10 +35,18 @@ export const meta = {
 				'en-US': 'Parent folder ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFolder: {
+			message: 'No such folder.',
+			code: 'NO_SUCH_FOLDER',
+			id: '53326628-a00d-40a6-a3cd-8975105c0f95'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// If the parent folder is specified
 	let parent = null;
 	if (ps.parentId) {
@@ -49,7 +58,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			});
 
 		if (parent === null) {
-			return rej('parent-not-found');
+			throw new ApiError(meta.errors.noSuchFolder);
 		}
 	}
 
@@ -61,12 +70,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		userId: user._id
 	});
 
-	// Serialize
 	const folderObj = await pack(folder);
 
-	// Response
-	res(folderObj);
-
 	// Publish folderCreated event
 	publishDriveStream(user._id, 'folderCreated', folderObj);
-}));
+
+	return folderObj;
+});
diff --git a/src/server/api/endpoints/drive/folders/delete.ts b/src/server/api/endpoints/drive/folders/delete.ts
index 228e262ccd..26a71d57df 100644
--- a/src/server/api/endpoints/drive/folders/delete.ts
+++ b/src/server/api/endpoints/drive/folders/delete.ts
@@ -4,6 +4,7 @@ import DriveFolder from '../../../../../models/drive-folder';
 import define from '../../../define';
 import { publishDriveStream } from '../../../../../services/stream';
 import DriveFile from '../../../../../models/drive-file';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -26,10 +27,24 @@ export const meta = {
 				'en-US': 'Target folder ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFolder: {
+			message: 'No such folder.',
+			code: 'NO_SUCH_FOLDER',
+			id: '1069098f-c281-440f-b085-f9932edbe091'
+		},
+
+		hasChildFilesOrFolders: {
+			message: 'This folder has child files or folders.',
+			code: 'HAS_CHILD_FILES_OR_FOLDERS',
+			id: 'b0fc8a17-963c-405d-bfbc-859a487295e1'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Get folder
 	const folder = await DriveFolder
 		.findOne({
@@ -38,7 +53,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 	if (folder === null) {
-		return rej('folder-not-found');
+		throw new ApiError(meta.errors.noSuchFolder);
 	}
 
 	const [childFoldersCount, childFilesCount] = await Promise.all([
@@ -47,7 +62,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	]);
 
 	if (childFoldersCount !== 0 || childFilesCount !== 0) {
-		return rej('has-child-contents');
+		throw new ApiError(meta.errors.hasChildFilesOrFolders);
 	}
 
 	await DriveFolder.remove({ _id: folder._id });
@@ -55,5 +70,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	// Publish folderCreated event
 	publishDriveStream(user._id, 'folderDeleted', folder._id);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/drive/folders/find.ts b/src/server/api/endpoints/drive/folders/find.ts
index bbf496150a..25d89f9fbb 100644
--- a/src/server/api/endpoints/drive/folders/find.ts
+++ b/src/server/api/endpoints/drive/folders/find.ts
@@ -24,7 +24,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const folders = await DriveFolder
 		.find({
 			name: ps.name,
@@ -32,5 +32,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			parentId: ps.parentId
 		});
 
-	res(await Promise.all(folders.map(folder => pack(folder))));
-}));
+	return await Promise.all(folders.map(folder => pack(folder)));
+});
diff --git a/src/server/api/endpoints/drive/folders/show.ts b/src/server/api/endpoints/drive/folders/show.ts
index 9a7a11c6dd..0d98158b92 100644
--- a/src/server/api/endpoints/drive/folders/show.ts
+++ b/src/server/api/endpoints/drive/folders/show.ts
@@ -2,6 +2,7 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
 import DriveFolder, { pack } from '../../../../../models/drive-folder';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -24,10 +25,18 @@ export const meta = {
 				'en-US': 'Target folder ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFolder: {
+			message: 'No such folder.',
+			code: 'NO_SUCH_FOLDER',
+			id: 'd74ab9eb-bb09-4bba-bf24-fb58f761e1e9'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Get folder
 	const folder = await DriveFolder
 		.findOne({
@@ -36,11 +45,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 	if (folder === null) {
-		return rej('folder-not-found');
+		throw new ApiError(meta.errors.noSuchFolder);
 	}
 
-	// Serialize
-	res(await pack(folder, {
+	return await pack(folder, {
 		detail: true
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/drive/folders/update.ts b/src/server/api/endpoints/drive/folders/update.ts
index 9c515474cd..585664ba0a 100644
--- a/src/server/api/endpoints/drive/folders/update.ts
+++ b/src/server/api/endpoints/drive/folders/update.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import DriveFolder, { isValidFolderName, pack } from '../../../../../models/drive-folder';
 import { publishDriveStream } from '../../../../../services/stream';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -42,10 +43,30 @@ export const meta = {
 				'en-US': 'Parent folder ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchFolder: {
+			message: 'No such folder.',
+			code: 'NO_SUCH_FOLDER',
+			id: 'f7974dac-2c0d-4a27-926e-23583b28e98e'
+		},
+
+		noSuchParentFolder: {
+			message: 'No such parent folder.',
+			code: 'NO_SUCH_PARENT_FOLDER',
+			id: 'ce104e3a-faaf-49d5-b459-10ff0cbbcaa1'
+		},
+
+		recursiveNesting: {
+			message: 'It can not be structured like nesting folders recursively.',
+			code: 'NO_SUCH_PARENT_FOLDER',
+			id: 'ce104e3a-faaf-49d5-b459-10ff0cbbcaa1'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch folder
 	const folder = await DriveFolder
 		.findOne({
@@ -54,7 +75,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 	if (folder === null) {
-		return rej('folder-not-found');
+		throw new ApiError(meta.errors.noSuchFolder);
 	}
 
 	if (ps.name) folder.name = ps.name;
@@ -71,7 +92,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 				});
 
 			if (parent === null) {
-				return rej('parent-folder-not-found');
+				throw new ApiError(meta.errors.noSuchParentFolder);
 			}
 
 			// Check if the circular reference will occur
@@ -95,7 +116,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 
 			if (parent.parentId !== null) {
 				if (await checkCircle(parent.parentId)) {
-					return rej('detected-circular-definition');
+					throw new ApiError(meta.errors.recursiveNesting);
 				}
 			}
 
@@ -111,12 +132,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	// Serialize
 	const folderObj = await pack(folder);
 
-	// Response
-	res(folderObj);
-
 	// Publish folderUpdated event
 	publishDriveStream(user._id, 'folderUpdated', folderObj);
-}));
+
+	return folderObj;
+});
diff --git a/src/server/api/endpoints/drive/stream.ts b/src/server/api/endpoints/drive/stream.ts
index c48ed8c37c..d5872470fd 100644
--- a/src/server/api/endpoints/drive/stream.ts
+++ b/src/server/api/endpoints/drive/stream.ts
@@ -30,12 +30,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	const sort = {
 		_id: -1
 	};
@@ -66,5 +61,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await packMany(files, { self: true }));
-}));
+		return await packMany(files, { self: true });
+});
diff --git a/src/server/api/endpoints/federation/instances.ts b/src/server/api/endpoints/federation/instances.ts
index 3df24cc84a..34da9dff7b 100644
--- a/src/server/api/endpoints/federation/instances.ts
+++ b/src/server/api/endpoints/federation/instances.ts
@@ -34,7 +34,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	let sort;
 
 	if (ps.sort) {
@@ -122,5 +122,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			skip: ps.offset
 		});
 
-	res(instances);
-}));
+	return instances;
+});
diff --git a/src/server/api/endpoints/federation/show-instance.ts b/src/server/api/endpoints/federation/show-instance.ts
index ad31c56afc..e443abcdaa 100644
--- a/src/server/api/endpoints/federation/show-instance.ts
+++ b/src/server/api/endpoints/federation/show-instance.ts
@@ -12,9 +12,9 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const instance = await Instance
 		.findOne({ host: ps.host });
 
-	res(instance);
-}));
+	return instance;
+});
diff --git a/src/server/api/endpoints/following/create.ts b/src/server/api/endpoints/following/create.ts
index b12b17d671..b4a58b996a 100644
--- a/src/server/api/endpoints/following/create.ts
+++ b/src/server/api/endpoints/following/create.ts
@@ -5,6 +5,7 @@ import User, { pack } from '../../../../models/user';
 import Following from '../../../../models/following';
 import create from '../../../../services/following/create';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -32,15 +33,47 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: 'fcd2eef9-a9b2-4c4f-8624-038099e90aa5'
+		},
+
+		followeeIsYourself: {
+			message: 'Followee is yourself.',
+			code: 'FOLLOWEE_IS_YOURSELF',
+			id: '26fbe7bb-a331-4857-af17-205b426669a9'
+		},
+
+		alreadyFollowing: {
+			message: 'You are already following that user.',
+			code: 'ALREADY_FOLLOWING',
+			id: '35387507-38c7-4cb9-9197-300b93783fa0'
+		},
+
+		blocking: {
+			message: 'You are blocking that user.',
+			code: 'BLOCKING',
+			id: '4e2206ec-aa4f-4960-b865-6c23ac38e2d9'
+		},
+
+		blocked: {
+			message: 'You are blocked by that user.',
+			code: 'BLOCKED',
+			id: 'c4ab57cc-4e41-45e9-bfd9-584f61e35ce0'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const follower = user;
 
 	// 自分自身
 	if (user._id.equals(ps.userId)) {
-		return rej('followee is yourself');
+		throw new ApiError(meta.errors.followeeIsYourself);
 	}
 
 	// Get followee
@@ -54,7 +87,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (followee === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Check if already following
@@ -64,16 +97,16 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist !== null) {
-		return rej('already following');
+		throw new ApiError(meta.errors.alreadyFollowing);
 	}
 
-	// Create following
 	try {
 		await create(follower, followee);
 	} catch (e) {
-		return rej(e && e.message ? e.message : e);
+		if (e.id === '710e8fb0-b8c3-4922-be49-d5d93d8e6a6e') throw new ApiError(meta.errors.blocking);
+		if (e.id === '3338392a-f764-498d-8855-db939dcf8c48') throw new ApiError(meta.errors.blocked);
+		throw e;
 	}
 
-	// Send response
-	res(await pack(followee._id, user));
-}));
+	return await pack(followee._id, user);
+});
diff --git a/src/server/api/endpoints/following/delete.ts b/src/server/api/endpoints/following/delete.ts
index dcc32079cc..6b6fac0719 100644
--- a/src/server/api/endpoints/following/delete.ts
+++ b/src/server/api/endpoints/following/delete.ts
@@ -5,6 +5,7 @@ import User, { pack } from '../../../../models/user';
 import Following from '../../../../models/following';
 import deleteFollowing from '../../../../services/following/delete';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -32,15 +33,35 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '5b12c78d-2b28-4dca-99d2-f56139b42ff8'
+		},
+
+		followeeIsYourself: {
+			message: 'Followee is yourself.',
+			code: 'FOLLOWEE_IS_YOURSELF',
+			id: 'd9e400b9-36b0-4808-b1d8-79e707f1296c'
+		},
+
+		notFollowing: {
+			message: 'You are not following that user.',
+			code: 'NOT_FOLLOWING',
+			id: '5dbf82f5-c92b-40b1-87d1-6c8c0741fd09'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const follower = user;
 
 	// Check if the followee is yourself
 	if (user._id.equals(ps.userId)) {
-		return rej('followee is yourself');
+		throw new ApiError(meta.errors.followeeIsYourself);
 	}
 
 	// Get followee
@@ -54,7 +75,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (followee === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Check not following
@@ -64,12 +85,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist === null) {
-		return rej('already not following');
+		throw new ApiError(meta.errors.notFollowing);
 	}
 
-	// Delete following
 	await deleteFollowing(follower, followee);
 
-	// Send response
-	res(await pack(followee._id, user));
-}));
+	return await pack(followee._id, user);
+});
diff --git a/src/server/api/endpoints/following/requests/accept.ts b/src/server/api/endpoints/following/requests/accept.ts
index 4d817ad982..2aa0434279 100644
--- a/src/server/api/endpoints/following/requests/accept.ts
+++ b/src/server/api/endpoints/following/requests/accept.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import acceptFollowRequest from '../../../../../services/following/requests/accept';
 import User from '../../../../../models/user';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -23,20 +24,28 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '66ce1645-d66c-46bb-8b79-96739af885bd'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch follower
 	const follower = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (follower === null) {
-		return rej('follower not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	await acceptFollowRequest(user, follower);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/following/requests/cancel.ts b/src/server/api/endpoints/following/requests/cancel.ts
index dff255eff5..bca9feaba9 100644
--- a/src/server/api/endpoints/following/requests/cancel.ts
+++ b/src/server/api/endpoints/following/requests/cancel.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import cancelFollowRequest from '../../../../../services/following/requests/cancel';
 import User, { pack } from '../../../../../models/user';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -23,24 +24,39 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '4e68c551-fc4c-4e46-bb41-7d4a37bf9dab'
+		},
+
+		followRequestNotFound: {
+			message: 'Follow request not found.',
+			code: 'FOLLOW_REQUEST_NOT_FOUND',
+			id: '089b125b-d338-482a-9a09-e2622ac9f8d4'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch followee
 	const followee = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (followee === null) {
-		return rej('followee not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	try {
 		await cancelFollowRequest(followee, user);
 	} catch (e) {
-		return rej(e);
+		if (e.id === '17447091-ce07-46dd-b331-c1fd4f15b1e7') throw new ApiError(meta.errors.followRequestNotFound);
+		throw e;
 	}
 
-	res(await pack(followee._id, user));
-}));
+	return await pack(followee._id, user);
+});
diff --git a/src/server/api/endpoints/following/requests/list.ts b/src/server/api/endpoints/following/requests/list.ts
index eee98a3658..f660277649 100644
--- a/src/server/api/endpoints/following/requests/list.ts
+++ b/src/server/api/endpoints/following/requests/list.ts
@@ -1,5 +1,3 @@
-// import $ from 'cafy';
-// import ID, { transform } from '../../../../../cafy-id';
 import FollowRequest, { pack } from '../../../../../models/follow-request';
 import define from '../../../define';
 
@@ -14,11 +12,10 @@ export const meta = {
 	kind: 'following-read'
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const reqs = await FollowRequest.find({
 		followeeId: user._id
 	});
 
-	// Send response
-	res(await Promise.all(reqs.map(req => pack(req))));
-}));
+	return await Promise.all(reqs.map(req => pack(req)));
+});
diff --git a/src/server/api/endpoints/following/requests/reject.ts b/src/server/api/endpoints/following/requests/reject.ts
index 59257d1373..760661b55f 100644
--- a/src/server/api/endpoints/following/requests/reject.ts
+++ b/src/server/api/endpoints/following/requests/reject.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import rejectFollowRequest from '../../../../../services/following/requests/reject';
 import User from '../../../../../models/user';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -23,20 +24,28 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: 'abc2ffa6-25b2-4380-ba99-321ff3a94555'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch follower
 	const follower = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (follower === null) {
-		return rej('follower not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	await rejectFollowRequest(user, follower);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/games/reversi/games.ts b/src/server/api/endpoints/games/reversi/games.ts
index fd9308f7e5..b188ba996d 100644
--- a/src/server/api/endpoints/games/reversi/games.ts
+++ b/src/server/api/endpoints/games/reversi/games.ts
@@ -27,12 +27,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	const q: any = ps.my ? {
 		isStarted: true,
 		$or: [{
@@ -65,8 +60,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		limit: ps.limit
 	});
 
-	// Reponse
-	res(Promise.all(games.map(async (g) => await pack(g, user, {
+	return await Promise.all(games.map((g) => pack(g, user, {
 		detail: false
-	}))));
-}));
+	})));
+});
diff --git a/src/server/api/endpoints/games/reversi/games/show.ts b/src/server/api/endpoints/games/reversi/games/show.ts
index 212d72bb7b..d70ab8de92 100644
--- a/src/server/api/endpoints/games/reversi/games/show.ts
+++ b/src/server/api/endpoints/games/reversi/games/show.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../../misc/cafy-id';
 import ReversiGame, { pack } from '../../../../../../models/games/reversi/game';
 import Reversi from '../../../../../../games/reversi/core';
 import define from '../../../../define';
+import { ApiError } from '../../../../error';
 
 export const meta = {
 	params: {
@@ -10,14 +11,22 @@ export const meta = {
 			validator: $.type(ID),
 			transform: transform,
 		},
+	},
+
+	errors: {
+		noSuchGame: {
+			message: 'No such game.',
+			code: 'NO_SUCH_GAME',
+			id: 'f13a03db-fae1-46c9-87f3-43c8165419e1'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const game = await ReversiGame.findOne({ _id: ps.gameId });
 
 	if (game == null) {
-		return rej('game not found');
+		throw new ApiError(meta.errors.noSuchGame);
 	}
 
 	const o = new Reversi(game.settings.map, {
@@ -31,8 +40,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 
 	const packed = await pack(game, user);
 
-	res(Object.assign({
+	return Object.assign({
 		board: o.board,
 		turn: o.turn
-	}, packed));
-}));
+	}, packed);
+});
diff --git a/src/server/api/endpoints/games/reversi/games/surrender.ts b/src/server/api/endpoints/games/reversi/games/surrender.ts
index a19743fee9..954ae07ebc 100644
--- a/src/server/api/endpoints/games/reversi/games/surrender.ts
+++ b/src/server/api/endpoints/games/reversi/games/surrender.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../../misc/cafy-id';
 import ReversiGame, { pack } from '../../../../../../models/games/reversi/game';
 import { publishReversiGameStream } from '../../../../../../services/stream';
 import define from '../../../../define';
+import { ApiError } from '../../../../error';
 
 export const meta = {
 	desc: {
@@ -19,22 +20,42 @@ export const meta = {
 				'ja-JP': '投了したい対局'
 			}
 		}
+	},
+
+	errors: {
+		noSuchGame: {
+			message: 'No such game.',
+			code: 'NO_SUCH_GAME',
+			id: 'ace0b11f-e0a6-4076-a30d-e8284c81b2df'
+		},
+
+		alreadyEnded: {
+			message: 'That game has already ended.',
+			code: 'ALREADY_ENDED',
+			id: '6c2ad4a6-cbf1-4a5b-b187-b772826cfc6d'
+		},
+
+		accessDenied: {
+			message: 'Access denied.',
+			code: 'ACCESS_DENIED',
+			id: '6e04164b-a992-4c93-8489-2123069973e1'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const game = await ReversiGame.findOne({ _id: ps.gameId });
 
 	if (game == null) {
-		return rej('game not found');
+		throw new ApiError(meta.errors.noSuchGame);
 	}
 
 	if (game.isEnded) {
-		return rej('this game is already ended');
+		throw new ApiError(meta.errors.alreadyEnded);
 	}
 
 	if (!game.user1Id.equals(user._id) && !game.user2Id.equals(user._id)) {
-		return rej('access denied');
+		throw new ApiError(meta.errors.accessDenied);
 	}
 
 	const winnerId = game.user1Id.equals(user._id) ? game.user2Id : game.user1Id;
@@ -54,5 +75,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		game: await pack(game._id, user)
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/games/reversi/invitations.ts b/src/server/api/endpoints/games/reversi/invitations.ts
index d808ff2e78..034c84bdd5 100644
--- a/src/server/api/endpoints/games/reversi/invitations.ts
+++ b/src/server/api/endpoints/games/reversi/invitations.ts
@@ -5,7 +5,7 @@ export const meta = {
 	requireCredential: true
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Find session
 	const invitations = await Matching.find({
 		childId: user._id
@@ -15,6 +15,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	// Reponse
-	res(Promise.all(invitations.map(async (i) => await packMatching(i, user))));
-}));
+	return await Promise.all(invitations.map((i) => packMatching(i, user)));
+});
diff --git a/src/server/api/endpoints/games/reversi/match.ts b/src/server/api/endpoints/games/reversi/match.ts
index febf815067..4fd4aedc15 100644
--- a/src/server/api/endpoints/games/reversi/match.ts
+++ b/src/server/api/endpoints/games/reversi/match.ts
@@ -6,6 +6,7 @@ import User from '../../../../../models/user';
 import { publishMainStream, publishReversiStream } from '../../../../../services/stream';
 import { eighteight } from '../../../../../games/reversi/maps';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	requireCredential: true,
@@ -19,13 +20,27 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		},
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '0b4f0559-b484-4e31-9581-3f73cee89b28'
+		},
+
+		isYourself: {
+			message: 'Target user is yourself.',
+			code: 'TARGET_IS_YOURSELF',
+			id: '96fd7bd6-d2bc-426c-a865-d055dcd2828e'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Myself
 	if (ps.userId.equals(user._id)) {
-		return rej('invalid userId param');
+		throw new ApiError(meta.errors.isYourself);
 	}
 
 	// Find session
@@ -57,9 +72,6 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			}
 		});
 
-		// Reponse
-		res(await packGame(game, user));
-
 		publishReversiStream(exist.parentId, 'matched', await packGame(game, exist.parentId));
 
 		const other = await Matching.count({
@@ -69,6 +81,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		if (other == 0) {
 			publishMainStream(user._id, 'reversiNoInvites');
 		}
+
+		return await packGame(game, user);
 	} else {
 		// Fetch child
 		const child = await User.findOne({
@@ -80,7 +94,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 		if (child === null) {
-			return rej('user not found');
+			throw new ApiError(meta.errors.noSuchUser);
 		}
 
 		// 以前のセッションはすべて削除しておく
@@ -95,14 +109,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			childId: child._id
 		});
 
-		// Reponse
-		res();
-
 		const packed = await packMatching(matching, child);
-
-		// 招待
 		publishReversiStream(child._id, 'invited', packed);
-
 		publishMainStream(child._id, 'reversiInvited', packed);
+
+		return;
 	}
-}));
+});
diff --git a/src/server/api/endpoints/games/reversi/match/cancel.ts b/src/server/api/endpoints/games/reversi/match/cancel.ts
index ac51e416ed..03b76babd7 100644
--- a/src/server/api/endpoints/games/reversi/match/cancel.ts
+++ b/src/server/api/endpoints/games/reversi/match/cancel.ts
@@ -5,10 +5,10 @@ export const meta = {
 	requireCredential: true
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	await Matching.remove({
 		parentId: user._id
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/hashtags/list.ts b/src/server/api/endpoints/hashtags/list.ts
index 5f197a8726..bfeba1d168 100644
--- a/src/server/api/endpoints/hashtags/list.ts
+++ b/src/server/api/endpoints/hashtags/list.ts
@@ -60,7 +60,7 @@ const sort: any = {
 	'-attachedRemoteUsers': { attachedRemoteUsersCount: 1 },
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const q = {} as any;
 	if (ps.attachedToUserOnly) q.attachedUsersCount = { $ne: 0 };
 	if (ps.attachedToLocalUserOnly) q.attachedLocalUsersCount = { $ne: 0 };
@@ -80,5 +80,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			}
 		});
 
-	res(tags);
-}));
+	return tags;
+});
diff --git a/src/server/api/endpoints/hashtags/search.ts b/src/server/api/endpoints/hashtags/search.ts
index dee776c1f6..eff50f4134 100644
--- a/src/server/api/endpoints/hashtags/search.ts
+++ b/src/server/api/endpoints/hashtags/search.ts
@@ -36,7 +36,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	const hashtags = await Hashtag
 		.find({
 			tag: new RegExp('^' + escapeRegexp(ps.query.toLowerCase()))
@@ -48,5 +48,5 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 			skip: ps.offset
 		});
 
-	res(hashtags.map(tag => tag.tag));
-}));
+	return hashtags.map(tag => tag.tag);
+});
diff --git a/src/server/api/endpoints/hashtags/trend.ts b/src/server/api/endpoints/hashtags/trend.ts
index d4efe5d910..bf036642d0 100644
--- a/src/server/api/endpoints/hashtags/trend.ts
+++ b/src/server/api/endpoints/hashtags/trend.ts
@@ -19,7 +19,7 @@ export const meta = {
 	requireCredential: false,
 };
 
-export default define(meta, () => new Promise(async (res, rej) => {
+export default define(meta, async () => {
 	const instance = await fetchMeta();
 	const hidedTags = instance.hidedTags.map(t => t.toLowerCase());
 
@@ -49,7 +49,7 @@ export default define(meta, () => new Promise(async (res, rej) => {
 	//#endregion
 
 	if (data.length == 0) {
-		return res([]);
+		return [];
 	}
 
 	const tags: {
@@ -141,5 +141,5 @@ export default define(meta, () => new Promise(async (res, rej) => {
 		usersCount: totalCounts[i].length
 	}));
 
-	res(stats);
-}));
+	return stats;
+});
diff --git a/src/server/api/endpoints/hashtags/users.ts b/src/server/api/endpoints/hashtags/users.ts
index be6b53b889..b77bdf6aa8 100644
--- a/src/server/api/endpoints/hashtags/users.ts
+++ b/src/server/api/endpoints/hashtags/users.ts
@@ -54,7 +54,7 @@ const sort: any = {
 	'-updatedAt': { updatedAt: 1 },
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const q = {
 		tags: ps.tag,
 		$and: []
@@ -79,5 +79,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			sort: sort[ps.sort],
 		});
 
-	res(await Promise.all(users.map(user => pack(user, me, { detail: true }))));
-}));
+	return await Promise.all(users.map(user => pack(user, me, { detail: true })));
+});
diff --git a/src/server/api/endpoints/i.ts b/src/server/api/endpoints/i.ts
index ab85b17d09..7ef4ddd264 100644
--- a/src/server/api/endpoints/i.ts
+++ b/src/server/api/endpoints/i.ts
@@ -18,13 +18,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user, app) => {
 	const isSecure = user != null && app == null;
 
-	// Serialize
-	res(await pack(user, user, {
+	return await pack(user, user, {
 		detail: true,
 		includeHasUnreadNotes: true,
 		includeSecrets: isSecure
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/i/2fa/done.ts b/src/server/api/endpoints/i/2fa/done.ts
index 2ee0c8886e..556354c386 100644
--- a/src/server/api/endpoints/i/2fa/done.ts
+++ b/src/server/api/endpoints/i/2fa/done.ts
@@ -15,11 +15,11 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const _token = ps.token.replace(/\s/g, '');
 
 	if (user.twoFactorTempSecret == null) {
-		return rej('二段階認証の設定が開始されていません');
+		throw new Error('二段階認証の設定が開始されていません');
 	}
 
 	const verified = (speakeasy as any).totp.verify({
@@ -29,7 +29,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (!verified) {
-		return rej('not verified');
+		throw new Error('not verified');
 	}
 
 	await User.update(user._id, {
@@ -39,5 +39,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/2fa/register.ts b/src/server/api/endpoints/i/2fa/register.ts
index 38e3ca7806..302b51ec0b 100644
--- a/src/server/api/endpoints/i/2fa/register.ts
+++ b/src/server/api/endpoints/i/2fa/register.ts
@@ -18,12 +18,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Compare password
 	const same = await bcrypt.compare(ps.password, user.password);
 
 	if (!same) {
-		return rej('incorrect password');
+		throw new Error('incorrect password');
 	}
 
 	// Generate user's secret key
@@ -38,17 +38,17 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	// Get the data URL of the authenticator URL
-	QRCode.toDataURL(speakeasy.otpauthURL({
+	const dataUrl = await QRCode.toDataURL(speakeasy.otpauthURL({
 		secret: secret.base32,
 		encoding: 'base32',
 		label: user.username,
 		issuer: config.host
-	}), (err, data_url) => {
-		res({
-			qr: data_url,
-			secret: secret.base32,
-			label: user.username,
-			issuer: config.host
-		});
-	});
-}));
+	}));
+
+	return {
+		qr: dataUrl,
+		secret: secret.base32,
+		label: user.username,
+		issuer: config.host
+	};
+});
diff --git a/src/server/api/endpoints/i/2fa/unregister.ts b/src/server/api/endpoints/i/2fa/unregister.ts
index 2cb48d93cd..37b2639198 100644
--- a/src/server/api/endpoints/i/2fa/unregister.ts
+++ b/src/server/api/endpoints/i/2fa/unregister.ts
@@ -15,12 +15,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Compare password
 	const same = await bcrypt.compare(ps.password, user.password);
 
 	if (!same) {
-		return rej('incorrect password');
+		throw new Error('incorrect password');
 	}
 
 	await User.update(user._id, {
@@ -30,5 +30,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/authorized_apps.ts b/src/server/api/endpoints/i/authorized_apps.ts
index 3e60afe698..cb8be9ed97 100644
--- a/src/server/api/endpoints/i/authorized_apps.ts
+++ b/src/server/api/endpoints/i/authorized_apps.ts
@@ -26,7 +26,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Get tokens
 	const tokens = await AccessToken
 		.find({
@@ -39,7 +39,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			}
 		});
 
-	res(await Promise.all(tokens.map(token => pack(token.appId, user, {
+	return await Promise.all(tokens.map(token => pack(token.appId, user, {
 		detail: true
-	}))));
-}));
+	})));
+});
diff --git a/src/server/api/endpoints/i/change_password.ts b/src/server/api/endpoints/i/change_password.ts
index a2cfc6f70e..8ab286b4bf 100644
--- a/src/server/api/endpoints/i/change_password.ts
+++ b/src/server/api/endpoints/i/change_password.ts
@@ -19,12 +19,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Compare password
 	const same = await bcrypt.compare(ps.currentPassword, user.password);
 
 	if (!same) {
-		return rej('incorrect password');
+		throw new Error('incorrect password');
 	}
 
 	// Generate hash of password
@@ -37,5 +37,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/clear-follow-request-notification.ts b/src/server/api/endpoints/i/clear-follow-request-notification.ts
index af4302621b..2c656965d5 100644
--- a/src/server/api/endpoints/i/clear-follow-request-notification.ts
+++ b/src/server/api/endpoints/i/clear-follow-request-notification.ts
@@ -10,12 +10,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	await User.update({ _id: user._id }, {
 		$set: {
 			pendingReceivedFollowRequestsCount: 0
 		}
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/delete-account.ts b/src/server/api/endpoints/i/delete-account.ts
index 6cab3d1394..e1b3093d1a 100644
--- a/src/server/api/endpoints/i/delete-account.ts
+++ b/src/server/api/endpoints/i/delete-account.ts
@@ -18,12 +18,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Compare password
 	const same = await bcrypt.compare(ps.password, user.password);
 
 	if (!same) {
-		return rej('incorrect password');
+		throw new Error('incorrect password');
 	}
 
 	await User.update({ _id: user._id }, {
@@ -49,5 +49,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	createDeleteNotesJob(user);
 	createDeleteDriveFilesJob(user);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/export-blocking.ts b/src/server/api/endpoints/i/export-blocking.ts
index 12a08c6d7d..346b29c79d 100644
--- a/src/server/api/endpoints/i/export-blocking.ts
+++ b/src/server/api/endpoints/i/export-blocking.ts
@@ -11,8 +11,8 @@ export const meta = {
 	},
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	createExportBlockingJob(user);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/export-following.ts b/src/server/api/endpoints/i/export-following.ts
index e819898d9b..5977b03105 100644
--- a/src/server/api/endpoints/i/export-following.ts
+++ b/src/server/api/endpoints/i/export-following.ts
@@ -11,8 +11,8 @@ export const meta = {
 	},
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	createExportFollowingJob(user);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/export-mute.ts b/src/server/api/endpoints/i/export-mute.ts
index c719a1f6a5..22ceff3631 100644
--- a/src/server/api/endpoints/i/export-mute.ts
+++ b/src/server/api/endpoints/i/export-mute.ts
@@ -11,8 +11,8 @@ export const meta = {
 	},
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	createExportMuteJob(user);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/export-notes.ts b/src/server/api/endpoints/i/export-notes.ts
index 6da6e68b9d..2881aa2697 100644
--- a/src/server/api/endpoints/i/export-notes.ts
+++ b/src/server/api/endpoints/i/export-notes.ts
@@ -11,8 +11,8 @@ export const meta = {
 	},
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	createExportNotesJob(user);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/favorites.ts b/src/server/api/endpoints/i/favorites.ts
index c476844b4b..b9bef38c69 100644
--- a/src/server/api/endpoints/i/favorites.ts
+++ b/src/server/api/endpoints/i/favorites.ts
@@ -31,12 +31,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	const query = {
 		userId: user._id
 	} as any;
@@ -63,5 +58,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await packMany(favorites, user));
-}));
+	return await packMany(favorites, user);
+});
diff --git a/src/server/api/endpoints/i/notifications.ts b/src/server/api/endpoints/i/notifications.ts
index 6287e42622..693d279965 100644
--- a/src/server/api/endpoints/i/notifications.ts
+++ b/src/server/api/endpoints/i/notifications.ts
@@ -55,12 +55,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	const hideUserIds = await getHideUserIds(user);
 
 	const query = {
@@ -114,10 +109,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await packMany(notifications));
-
 	// Mark all as read
 	if (notifications.length > 0 && ps.markAsRead) {
 		read(user._id, notifications);
 	}
-}));
+
+	return await packMany(notifications);
+});
diff --git a/src/server/api/endpoints/i/pin.ts b/src/server/api/endpoints/i/pin.ts
index 79a3e42fb7..0b6b1b0db9 100644
--- a/src/server/api/endpoints/i/pin.ts
+++ b/src/server/api/endpoints/i/pin.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../misc/cafy-id';
 import { pack } from '../../../../models/user';
 import { addPinned } from '../../../../services/i/pin';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -24,22 +25,38 @@ export const meta = {
 				'en-US': 'Target note ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '56734f8b-3928-431e-bf80-6ff87df40cb3'
+		},
+
+		pinLimitExceeded: {
+			message: 'You can not pin notes any more.',
+			code: 'PIN_LIMIT_EXCEEDED',
+			id: '72dab508-c64d-498f-8740-a8eec1ba385a'
+		},
+
+		alreadyPinned: {
+			message: 'That note has already been pinned.',
+			code: 'ALREADY_PINNED',
+			id: '8b18c2b7-68fe-4edb-9892-c0cbaeb6c913'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Processing
-	try {
-		await addPinned(user, ps.noteId);
-	} catch (e) {
-		return rej(e.message);
-	}
-
-	// Serialize
-	const iObj = await pack(user, user, {
-		detail: true
+export default define(meta, async (ps, user) => {
+	await addPinned(user, ps.noteId).catch(e => {
+		if (e.id === '70c4e51f-5bea-449c-a030-53bee3cce202') throw new ApiError(meta.errors.noSuchNote);
+		if (e.id === '15a018eb-58e5-4da1-93be-330fcc5e4e1a') throw new ApiError(meta.errors.pinLimitExceeded);
+		if (e.id === '23f0cf4e-59a3-4276-a91d-61a5891c1514') throw new ApiError(meta.errors.alreadyPinned);
+		throw e;
 	});
 
-	// Send response
-	res(iObj);
-}));
+	return await pack(user, user, {
+		detail: true
+	});
+});
diff --git a/src/server/api/endpoints/i/read_all_messaging_messages.ts b/src/server/api/endpoints/i/read_all_messaging_messages.ts
index 739acf93c6..6bc6e16b4d 100644
--- a/src/server/api/endpoints/i/read_all_messaging_messages.ts
+++ b/src/server/api/endpoints/i/read_all_messaging_messages.ts
@@ -17,7 +17,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Update documents
 	await Message.update({
 		recipientId: user._id,
@@ -38,5 +38,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 
 	publishMainStream(user._id, 'readAllMessagingMessages');
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/read_all_unread_notes.ts b/src/server/api/endpoints/i/read_all_unread_notes.ts
index 509450e43c..16db17cb04 100644
--- a/src/server/api/endpoints/i/read_all_unread_notes.ts
+++ b/src/server/api/endpoints/i/read_all_unread_notes.ts
@@ -17,7 +17,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Remove documents
 	await NoteUnread.remove({
 		userId: user._id
@@ -34,5 +34,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	publishMainStream(user._id, 'readAllUnreadMentions');
 	publishMainStream(user._id, 'readAllUnreadSpecifiedNotes');
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/i/regenerate_token.ts b/src/server/api/endpoints/i/regenerate_token.ts
index 16c2983184..ad10b99b36 100644
--- a/src/server/api/endpoints/i/regenerate_token.ts
+++ b/src/server/api/endpoints/i/regenerate_token.ts
@@ -17,12 +17,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Compare password
 	const same = await bcrypt.compare(ps.password, user.password);
 
 	if (!same) {
-		return rej('incorrect password');
+		throw new Error('incorrect password');
 	}
 
 	// Generate secret
@@ -34,8 +34,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-
 	// Publish event
 	publishMainStream(user._id, 'myTokenRegenerated');
-}));
+
+	return;
+});
diff --git a/src/server/api/endpoints/i/signin_history.ts b/src/server/api/endpoints/i/signin_history.ts
index cdffc6cc3c..87160a9f91 100644
--- a/src/server/api/endpoints/i/signin_history.ts
+++ b/src/server/api/endpoints/i/signin_history.ts
@@ -26,12 +26,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	const query = {
 		userId: user._id
 	} as any;
@@ -57,6 +52,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	// Serialize
-	res(await Promise.all(history.map(record => pack(record))));
-}));
+	return await Promise.all(history.map(record => pack(record)));
+});
diff --git a/src/server/api/endpoints/i/unpin.ts b/src/server/api/endpoints/i/unpin.ts
index 405c3cb9c5..472e811562 100644
--- a/src/server/api/endpoints/i/unpin.ts
+++ b/src/server/api/endpoints/i/unpin.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../misc/cafy-id';
 import { pack } from '../../../../models/user';
 import { removePinned } from '../../../../services/i/pin';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -24,22 +25,24 @@ export const meta = {
 				'en-US': 'Target note ID'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '454170ce-9d63-4a43-9da1-ea10afe81e21'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Processing
-	try {
-		await removePinned(user, ps.noteId);
-	} catch (e) {
-		return rej(e.message);
-	}
-
-	// Serialize
-	const iObj = await pack(user, user, {
-		detail: true
+export default define(meta, async (ps, user) => {
+	await removePinned(user, ps.noteId).catch(e => {
+		if (e.id === 'b302d4cf-c050-400a-bbb3-be208681f40c') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	// Send response
-	res(iObj);
-}));
+	return await pack(user, user, {
+		detail: true
+	});
+});
diff --git a/src/server/api/endpoints/i/update.ts b/src/server/api/endpoints/i/update.ts
index 1de7a807c0..df7da46774 100644
--- a/src/server/api/endpoints/i/update.ts
+++ b/src/server/api/endpoints/i/update.ts
@@ -12,6 +12,7 @@ import extractEmojis from '../../../../misc/extract-emojis';
 import extractHashtags from '../../../../misc/extract-hashtags';
 import * as langmap from 'langmap';
 import { updateHashtag } from '../../../../services/update-hashtag';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -131,10 +132,36 @@ export const meta = {
 				'ja-JP': 'アップロードするメディアをデフォルトで「閲覧注意」として設定するか'
 			}
 		},
+	},
+
+	errors: {
+		noSuchAvatar: {
+			message: 'No such avatar file.',
+			code: 'NO_SUCH_AVATAR',
+			id: '539f3a45-f215-4f81-a9a8-31293640207f'
+		},
+
+		noSuchBanner: {
+			message: 'No such banner file.',
+			code: 'NO_SUCH_BANNER',
+			id: '0d8f5629-f210-41c2-9433-735831a58595'
+		},
+
+		avatarNotAnImage: {
+			message: 'The file specified as an avatar is not an image.',
+			code: 'AVATAR_NOT_AN_IMAGE',
+			id: 'f419f9f8-2f4d-46b1-9fb4-49d3a2fd7191'
+		},
+
+		bannerNotAnImage: {
+			message: 'The file specified as a banner is not an image.',
+			code: 'BANNER_NOT_AN_IMAGE',
+			id: '75aedb19-2afd-4e6d-87fc-67941256fa60'
+		},
 	}
 };
 
-export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user, app) => {
 	const isSecure = user != null && app == null;
 
 	const updates = {} as any;
@@ -160,8 +187,8 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 			_id: ps.avatarId
 		});
 
-		if (avatar == null) return rej('avatar not found');
-		if (!avatar.contentType.startsWith('image/')) return rej('avatar not an image');
+		if (avatar == null) throw new ApiError(meta.errors.noSuchAvatar);
+		if (!avatar.contentType.startsWith('image/')) throw new ApiError(meta.errors.avatarNotAnImage);
 
 		updates.avatarUrl = getDriveFileUrl(avatar, true);
 
@@ -175,8 +202,8 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 			_id: ps.bannerId
 		});
 
-		if (banner == null) return rej('banner not found');
-		if (!banner.contentType.startsWith('image/')) return rej('banner not an image');
+		if (banner == null) throw new ApiError(meta.errors.noSuchBanner);
+		if (!banner.contentType.startsWith('image/')) throw new ApiError(meta.errors.bannerNotAnImage);
 
 		updates.bannerUrl = getDriveFileUrl(banner, false);
 
@@ -194,7 +221,7 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 				_id: ps.wallpaperId
 			});
 
-			if (wallpaper == null) return rej('wallpaper not found');
+			if (wallpaper == null) throw new Error('wallpaper not found');
 
 			updates.wallpaperUrl = getDriveFileUrl(wallpaper);
 
@@ -233,15 +260,11 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 		$set: updates
 	});
 
-	// Serialize
 	const iObj = await pack(user._id, user, {
 		detail: true,
 		includeSecrets: isSecure
 	});
 
-	// Send response
-	res(iObj);
-
 	// Publish meUpdated event
 	publishMainStream(user._id, 'meUpdated', iObj);
 
@@ -252,4 +275,6 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 
 	// フォロワーにUpdateを配信
 	publishToFollowers(user._id);
-}));
+
+	return iObj;
+});
diff --git a/src/server/api/endpoints/i/update_client_setting.ts b/src/server/api/endpoints/i/update_client_setting.ts
index 2157986f10..79cd04e169 100644
--- a/src/server/api/endpoints/i/update_client_setting.ts
+++ b/src/server/api/endpoints/i/update_client_setting.ts
@@ -19,7 +19,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const x: any = {};
 	x[`clientSettings.${ps.name}`] = ps.value;
 
@@ -27,11 +27,11 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		$set: x
 	});
 
-	res();
-
 	// Publish event
 	publishMainStream(user._id, 'clientSettingUpdated', {
 		key: ps.name,
 		value: ps.value
 	});
-}));
+
+	return;
+});
diff --git a/src/server/api/endpoints/i/update_email.ts b/src/server/api/endpoints/i/update_email.ts
index 8781c8ac93..c90462d850 100644
--- a/src/server/api/endpoints/i/update_email.ts
+++ b/src/server/api/endpoints/i/update_email.ts
@@ -31,12 +31,12 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Compare password
 	const same = await bcrypt.compare(ps.password, user.password);
 
 	if (!same) {
-		return rej('incorrect password');
+		throw new Error('incorrect password');
 	}
 
 	await User.update(user._id, {
@@ -47,15 +47,11 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	});
 
-	// Serialize
 	const iObj = await pack(user._id, user, {
 		detail: true,
 		includeSecrets: true
 	});
 
-	// Send response
-	res(iObj);
-
 	// Publish meUpdated event
 	publishMainStream(user._id, 'meUpdated', iObj);
 
@@ -99,4 +95,6 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			apiLogger.info('Message sent: %s', info.messageId);
 		});
 	}
-}));
+
+	return iObj;
+});
diff --git a/src/server/api/endpoints/i/update_home.ts b/src/server/api/endpoints/i/update_home.ts
index 805c52d728..e2c319887f 100644
--- a/src/server/api/endpoints/i/update_home.ts
+++ b/src/server/api/endpoints/i/update_home.ts
@@ -20,14 +20,14 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	await User.update(user._id, {
 		$set: {
 			'clientSettings.home': ps.home
 		}
 	});
 
-	res();
-
 	publishMainStream(user._id, 'homeUpdated', ps.home);
-}));
+
+	return;
+});
diff --git a/src/server/api/endpoints/i/update_mobile_home.ts b/src/server/api/endpoints/i/update_mobile_home.ts
index 0e1c3313e0..642e2b3e09 100644
--- a/src/server/api/endpoints/i/update_mobile_home.ts
+++ b/src/server/api/endpoints/i/update_mobile_home.ts
@@ -19,14 +19,14 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	await User.update(user._id, {
 		$set: {
 			'clientSettings.mobileHome': ps.home
 		}
 	});
 
-	res();
-
 	publishMainStream(user._id, 'mobileHomeUpdated', ps.home);
-}));
+
+	return;
+});
diff --git a/src/server/api/endpoints/i/update_widget.ts b/src/server/api/endpoints/i/update_widget.ts
index e3e91c1f08..67d342278d 100644
--- a/src/server/api/endpoints/i/update_widget.ts
+++ b/src/server/api/endpoints/i/update_widget.ts
@@ -19,8 +19,8 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	if (ps.id == null && ps.data == null) return rej('you need to set id and data params if home param unset');
+export default define(meta, async (ps, user) => {
+	if (ps.id == null && ps.data == null) throw new Error('you need to set id and data params if home param unset');
 
 	let widget;
 
@@ -81,8 +81,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			id: ps.id, data: ps.data
 		});
 
-		res();
+		return;
 	} else {
-		rej('widget not found');
+		throw new Error('widget not found');
 	}
-}));
+});
diff --git a/src/server/api/endpoints/messaging/history.ts b/src/server/api/endpoints/messaging/history.ts
index 408e2d42a6..e42bf79c54 100644
--- a/src/server/api/endpoints/messaging/history.ts
+++ b/src/server/api/endpoints/messaging/history.ts
@@ -21,7 +21,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const mute = await Mute.find({
 		muterId: user._id,
 		deletedAt: { $exists: false }
@@ -58,5 +58,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		}
 	}
 
-	res(await Promise.all(history.map(h => pack(h._id, user))));
-}));
+	return await Promise.all(history.map(h => pack(h._id, user)));
+});
diff --git a/src/server/api/endpoints/messaging/messages.ts b/src/server/api/endpoints/messaging/messages.ts
index 4c1b7206d6..9b27d4cac1 100644
--- a/src/server/api/endpoints/messaging/messages.ts
+++ b/src/server/api/endpoints/messaging/messages.ts
@@ -5,6 +5,7 @@ import User from '../../../../models/user';
 import { pack } from '../../../../models/messaging-message';
 import read from '../../common/read-messaging-message';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -45,15 +46,18 @@ export const meta = {
 			validator: $.optional.bool,
 			default: true
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '11795c64-40ea-4198-b06e-3c873ed9039d'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	// Fetch recipient
 	const recipient = await User.findOne({
 		_id: ps.userId
@@ -64,7 +68,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 	if (recipient === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	const query = {
@@ -98,16 +102,12 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await Promise.all(messages.map(message => pack(message, user, {
-		populateRecipient: false
-	}))));
-
-	if (messages.length === 0) {
-		return;
-	}
-
 	// Mark all as read
 	if (ps.markAsRead) {
 		read(user._id, recipient._id, messages);
 	}
-}));
+
+	return await Promise.all(messages.map(message => pack(message, user, {
+		populateRecipient: false
+	})));
+});
diff --git a/src/server/api/endpoints/messaging/messages/create.ts b/src/server/api/endpoints/messaging/messages/create.ts
index 96a047a9bf..3885d2583c 100644
--- a/src/server/api/endpoints/messaging/messages/create.ts
+++ b/src/server/api/endpoints/messaging/messages/create.ts
@@ -10,6 +10,7 @@ import { publishMainStream } from '../../../../../services/stream';
 import { publishMessagingStream, publishMessagingIndexStream } from '../../../../../services/stream';
 import pushSw from '../../../../../services/push-notification';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -39,13 +40,39 @@ export const meta = {
 			validator: $.optional.type(ID),
 			transform: transform,
 		}
+	},
+
+	errors: {
+		recipientIsYourself: {
+			message: 'You can not send a message to yourself.',
+			code: 'RECIPIENT_IS_YOURSELF',
+			id: '17e2ba79-e22a-4cbc-bf91-d327643f4a7e'
+		},
+
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '11795c64-40ea-4198-b06e-3c873ed9039d'
+		},
+
+		noSuchFile: {
+			message: 'No such file.',
+			code: 'NO_SUCH_FILE',
+			id: '4372b8e2-185d-4146-8749-2f68864a3e5f'
+		},
+
+		contentRequired: {
+			message: 'Content required. You need to set text or fileId.',
+			code: 'CONTENT_REQUIRED',
+			id: '25587321-b0e6-449c-9239-f8925092942c'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Myself
 	if (ps.userId.equals(user._id)) {
-		return rej('cannot send message to myself');
+		throw new ApiError(meta.errors.recipientIsYourself);
 	}
 
 	// Fetch recipient
@@ -58,7 +85,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (recipient === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	let file = null;
@@ -69,16 +96,15 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		});
 
 		if (file === null) {
-			return rej('file not found');
+			throw new ApiError(meta.errors.noSuchFile);
 		}
 	}
 
 	// テキストが無いかつ添付ファイルも無かったらエラー
 	if (ps.text == null && file == null) {
-		return rej('text or file is required');
+		throw new ApiError(meta.errors.contentRequired);
 	}
 
-	// メッセージを作成
 	const message = await Message.insert({
 		createdAt: new Date(),
 		fileId: file ? file._id : undefined,
@@ -88,12 +114,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		isRead: false
 	});
 
-	// Serialize
 	const messageObj = await pack(message);
 
-	// Reponse
-	res(messageObj);
-
 	// 自分のストリーム
 	publishMessagingStream(message.userId, message.recipientId, 'message', messageObj);
 	publishMessagingIndexStream(message.userId, 'message', messageObj);
@@ -131,4 +153,6 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			pushSw(message.recipientId, 'unreadMessagingMessage', messageObj);
 		}
 	}, 2000);
-}));
+
+	return messageObj;
+});
diff --git a/src/server/api/endpoints/messaging/messages/delete.ts b/src/server/api/endpoints/messaging/messages/delete.ts
index 4f3fabb4ce..5bc492c19d 100644
--- a/src/server/api/endpoints/messaging/messages/delete.ts
+++ b/src/server/api/endpoints/messaging/messages/delete.ts
@@ -4,6 +4,7 @@ import Message from '../../../../../models/messaging-message';
 import define from '../../../define';
 import { publishMessagingStream } from '../../../../../services/stream';
 import * as ms from 'ms';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -32,17 +33,25 @@ export const meta = {
 				'en-US': 'Target message ID.'
 			}
 		}
+	},
+
+	errors: {
+		noSuchMessage: {
+			message: 'No such message.',
+			code: 'NO_SUCH_MESSAGE',
+			id: '54b5b326-7925-42cf-8019-130fda8b56af'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const message = await Message.findOne({
 		_id: ps.messageId,
 		userId: user._id
 	});
 
 	if (message === null) {
-		return rej('message not found');
+		throw new ApiError(meta.errors.noSuchMessage);
 	}
 
 	await Message.remove({ _id: message._id });
@@ -50,5 +59,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	publishMessagingStream(message.userId, message.recipientId, 'deleted', message._id);
 	publishMessagingStream(message.recipientId, message.userId, 'deleted', message._id);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/messaging/messages/read.ts b/src/server/api/endpoints/messaging/messages/read.ts
index 8343ea28ca..98f195d753 100644
--- a/src/server/api/endpoints/messaging/messages/read.ts
+++ b/src/server/api/endpoints/messaging/messages/read.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import Message from '../../../../../models/messaging-message';
 import read from '../../../common/read-messaging-message';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -23,20 +24,28 @@ export const meta = {
 				'en-US': 'The ID of a message that you want to mark as read'
 			}
 		}
+	},
+
+	errors: {
+		noSuchMessage: {
+			message: 'No such message.',
+			code: 'NO_SUCH_MESSAGE',
+			id: '86d56a2f-a9c3-4afb-b13c-3e9bfef9aa14'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const message = await Message.findOne({
 		_id: ps.messageId,
 		recipientId: user._id
 	});
 
 	if (message == null) {
-		return rej('message not found');
+		throw new ApiError(meta.errors.noSuchMessage);
 	}
 
 	read(user._id, message.userId, message);
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/meta.ts b/src/server/api/endpoints/meta.ts
index b9f458e9a6..82769506c6 100644
--- a/src/server/api/endpoints/meta.ts
+++ b/src/server/api/endpoints/meta.ts
@@ -24,7 +24,7 @@ export const meta = {
 	},
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const instance = await fetchMeta();
 
 	const emojis = await Emoji.find({ host: null }, {
@@ -118,5 +118,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		response.swPrivateKey = instance.swPrivateKey;
 	}
 
-	res(response);
-}));
+	return response;
+});
diff --git a/src/server/api/endpoints/mute/create.ts b/src/server/api/endpoints/mute/create.ts
index d25887fb45..166900e62f 100644
--- a/src/server/api/endpoints/mute/create.ts
+++ b/src/server/api/endpoints/mute/create.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../misc/cafy-id';
 import User from '../../../../models/user';
 import Mute from '../../../../models/mute';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -23,15 +24,35 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		},
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '6fef56f3-e765-4957-88e5-c6f65329b8a5'
+		},
+
+		muteeIsYourself: {
+			message: 'Mutee is yourself.',
+			code: 'MUTEE_IS_YOURSELF',
+			id: 'a4619cb2-5f23-484b-9301-94c903074e10'
+		},
+
+		alreadyMuting: {
+			message: 'You are already muting that user.',
+			code: 'ALREADY_MUTING',
+			id: '7e7359cb-160c-4956-b08f-4d1c653cd007'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const muter = user;
 
 	// 自分自身
 	if (user._id.equals(ps.userId)) {
-		return rej('mutee is yourself');
+		throw new ApiError(meta.errors.muteeIsYourself);
 	}
 
 	// Get mutee
@@ -45,7 +66,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (mutee === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Check if already muting
@@ -55,7 +76,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist !== null) {
-		return rej('already muting');
+		throw new ApiError(meta.errors.alreadyMuting);
 	}
 
 	// Create mute
@@ -65,5 +86,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		muteeId: mutee._id,
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/mute/delete.ts b/src/server/api/endpoints/mute/delete.ts
index 4c59ede6d2..1d74c45ef1 100644
--- a/src/server/api/endpoints/mute/delete.ts
+++ b/src/server/api/endpoints/mute/delete.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../misc/cafy-id';
 import User from '../../../../models/user';
 import Mute from '../../../../models/mute';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -23,15 +24,35 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		},
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: 'b851d00b-8ab1-4a56-8b1b-e24187cb48ef'
+		},
+
+		muteeIsYourself: {
+			message: 'Mutee is yourself.',
+			code: 'MUTEE_IS_YOURSELF',
+			id: 'f428b029-6b39-4d48-a1d2-cc1ae6dd5cf9'
+		},
+
+		notMuting: {
+			message: 'You are not muting that user.',
+			code: 'NOT_MUTING',
+			id: '5467d020-daa9-4553-81e1-135c0c35a96d'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const muter = user;
 
 	// Check if the mutee is yourself
 	if (user._id.equals(ps.userId)) {
-		return rej('mutee is yourself');
+		throw new ApiError(meta.errors.muteeIsYourself);
 	}
 
 	// Get mutee
@@ -45,7 +66,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (mutee === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Check not muting
@@ -55,7 +76,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist === null) {
-		return rej('already not muting');
+		throw new ApiError(meta.errors.notMuting);
 	}
 
 	// Delete mute
@@ -63,5 +84,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		_id: exist._id
 	});
 
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/mute/list.ts b/src/server/api/endpoints/mute/list.ts
index ffe1f971d5..84699c2373 100644
--- a/src/server/api/endpoints/mute/list.ts
+++ b/src/server/api/endpoints/mute/list.ts
@@ -31,12 +31,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, me) => {
 	const query = {
 		muterId: me._id
 	} as any;
@@ -62,5 +57,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			sort: sort
 		});
 
-	res(await packMany(mutes, me));
-}));
+	return await packMany(mutes, me);
+});
diff --git a/src/server/api/endpoints/my/apps.ts b/src/server/api/endpoints/my/apps.ts
index 0a95707396..0eeeb5f858 100644
--- a/src/server/api/endpoints/my/apps.ts
+++ b/src/server/api/endpoints/my/apps.ts
@@ -23,12 +23,11 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const query = {
 		userId: user._id
 	};
 
-	// Execute query
 	const apps = await App
 		.find(query, {
 			limit: ps.limit,
@@ -38,8 +37,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			}
 		});
 
-	// Reply
-	res(await Promise.all(apps.map(app => pack(app, user, {
+	return await Promise.all(apps.map(app => pack(app, user, {
 		detail: true
-	}))));
-}));
+	})));
+});
diff --git a/src/server/api/endpoints/notes.ts b/src/server/api/endpoints/notes.ts
index f95ed19d2c..f8d6fdd2ba 100644
--- a/src/server/api/endpoints/notes.ts
+++ b/src/server/api/endpoints/notes.ts
@@ -68,13 +68,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
-	// Construct query
+export default define(meta, async (ps) => {
 	const sort = {
 		_id: -1
 	};
@@ -119,13 +113,10 @@ export default define(meta, (ps) => new Promise(async (res, rej) => {
 	//	query.isBot = bot;
 	//}
 
-	// Issue query
-	const notes = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
+	const notes = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
-	// Serialize
-	res(await packMany(notes));
-}));
+	return await packMany(notes);
+});
diff --git a/src/server/api/endpoints/notes/conversation.ts b/src/server/api/endpoints/notes/conversation.ts
index 848cf9e162..ec371ecf19 100644
--- a/src/server/api/endpoints/notes/conversation.ts
+++ b/src/server/api/endpoints/notes/conversation.ts
@@ -2,6 +2,8 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../misc/cafy-id';
 import Note, { packMany, INote } from '../../../../models/note';
 import define from '../../define';
+import { ApiError } from '../../error';
+import { getValiedNote } from '../../common/getters';
 
 export const meta = {
 	desc: {
@@ -30,19 +32,23 @@ export const meta = {
 			validator: $.optional.num.min(0),
 			default: 0
 		},
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: 'e1035875-9551-45ec-afa8-1ded1fcb53c8'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Lookup note
-	const note = await Note.findOne({
-		_id: ps.noteId
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	if (note === null) {
-		return rej('note not found');
-	}
-
 	const conversation: INote[] = [];
 	let i = 0;
 
@@ -67,5 +73,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		await get(note.replyId);
 	}
 
-	res(await packMany(conversation, user));
-}));
+	return await packMany(conversation, user);
+});
diff --git a/src/server/api/endpoints/notes/create.ts b/src/server/api/endpoints/notes/create.ts
index 47eebc186c..d24cd7b123 100644
--- a/src/server/api/endpoints/notes/create.ts
+++ b/src/server/api/endpoints/notes/create.ts
@@ -8,6 +8,7 @@ import DriveFile, { IDriveFile } from '../../../../models/drive-file';
 import create from '../../../../services/note/create';
 import define from '../../define';
 import fetchMeta from '../../../../misc/fetch-meta';
+import { ApiError } from '../../error';
 
 let maxNoteTextLength = 1000;
 
@@ -180,10 +181,42 @@ export const meta = {
 				}
 			}
 		}
+	},
+
+	errors: {
+		noSuchRenoteTarget: {
+			message: 'No such renote target.',
+			code: 'NO_SUCH_RENOTE_TARGET',
+			id: 'b5c90186-4ab0-49c8-9bba-a1f76c282ba4'
+		},
+
+		cannotReRenote: {
+			message: 'You can not Renote a pure Renote.',
+			code: 'CANNOT_RENOTE_TO_A_PURE_RENOTE',
+			id: 'fd4cc33e-2a37-48dd-99cc-9b806eb2031a'
+		},
+
+		noSuchReplyTarget: {
+			message: 'No such reply target.',
+			code: 'NO_SUCH_REPLY_TARGET',
+			id: '749ee0f6-d3da-459a-bf02-282e2da4292c'
+		},
+
+		cannotReplyToPureRenote: {
+			message: 'You can not reply to a pure Renote.',
+			code: 'CANNOT_REPLY_TO_A_PURE_RENOTE',
+			id: '3ac74a84-8fd5-4bb0-870f-01804f82ce15'
+		},
+
+		contentRequired: {
+			message: 'Content required. You need to set text, fileIds, renoteId or poll.',
+			code: 'CONTENT_REQUIRED',
+			id: '6f57e42b-c348-439b-bc45-993995cc515a'
+		},
 	}
 };
 
-export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user, app) => {
 	let visibleUsers: IUser[] = [];
 	if (ps.visibleUserIds) {
 		visibleUsers = await Promise.all(ps.visibleUserIds.map(id => User.findOne({
@@ -212,9 +245,9 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 		});
 
 		if (renote == null) {
-			return rej('renoteee is not found');
+			throw new ApiError(meta.errors.noSuchRenoteTarget);
 		} else if (renote.renoteId && !renote.text && !renote.fileIds) {
-			return rej('cannot renote to renote');
+			throw new ApiError(meta.errors.cannotReRenote);
 		}
 	}
 
@@ -226,12 +259,12 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 		});
 
 		if (reply === null) {
-			return rej('in reply to note is not found');
+			throw new ApiError(meta.errors.noSuchReplyTarget);
 		}
 
 		// 返信対象が引用でないRenoteだったらエラー
 		if (reply.renoteId && !reply.text && !reply.fileIds) {
-			return rej('cannot reply to renote');
+			throw new ApiError(meta.errors.cannotReplyToPureRenote);
 		}
 	}
 
@@ -245,7 +278,7 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 
 	// テキストが無いかつ添付ファイルが無いかつRenoteも無いかつ投票も無かったらエラー
 	if (!(ps.text || files.length || renote || ps.poll)) {
-		return rej('text, fileIds, renoteId or poll is required');
+		throw new ApiError(meta.errors.contentRequired);
 	}
 
 	// 後方互換性のため
@@ -254,7 +287,7 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 	}
 
 	// 投稿を作成
-	create(user, {
+	const note = await create(user, {
 		createdAt: new Date(),
 		files: files,
 		poll: ps.poll,
@@ -271,14 +304,9 @@ export default define(meta, (ps, user, app) => new Promise(async (res, rej) => {
 		apHashtags: ps.noExtractHashtags ? [] : undefined,
 		apEmojis: ps.noExtractEmojis ? [] : undefined,
 		geo: ps.geo
-	})
-	.then(note => pack(note, user))
-	.then(noteObj => {
-		res({
-			createdNote: noteObj
-		});
-	})
-	.catch(e => {
-		rej(e);
 	});
-}));
+
+	return {
+		createdNote: await pack(note, user)
+	};
+});
diff --git a/src/server/api/endpoints/notes/delete.ts b/src/server/api/endpoints/notes/delete.ts
index 261c7ad547..42f7494184 100644
--- a/src/server/api/endpoints/notes/delete.ts
+++ b/src/server/api/endpoints/notes/delete.ts
@@ -1,10 +1,11 @@
 import $ from 'cafy';
 import ID, { transform } from '../../../../misc/cafy-id';
-import Note from '../../../../models/note';
 import deleteNote from '../../../../services/note/delete';
 import User from '../../../../models/user';
 import define from '../../define';
 import * as ms from 'ms';
+import { getValiedNote } from '../../common/getters';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -33,24 +34,32 @@ export const meta = {
 				'en-US': 'Target note ID.'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '490be23f-8c1f-4796-819f-94cb4f9d1630'
+		},
+
+		accessDenied: {
+			message: 'Access denied.',
+			code: 'ACCESS_DENIED',
+			id: 'fe8d7103-0ea8-4ec3-814d-f8b401dc69e9'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Fetch note
-	const note = await Note.findOne({
-		_id: ps.noteId
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	if (note === null) {
-		return rej('note not found');
-	}
-
 	if (!user.isAdmin && !user.isModerator && !note.userId.equals(user._id)) {
-		return rej('access denied');
+		throw new ApiError(meta.errors.accessDenied);
 	}
 
 	await deleteNote(await User.findOne({ _id: note.userId }), note);
-
-	res();
-}));
+});
diff --git a/src/server/api/endpoints/notes/favorites/create.ts b/src/server/api/endpoints/notes/favorites/create.ts
index 8ec0891a31..bdb4aff72d 100644
--- a/src/server/api/endpoints/notes/favorites/create.ts
+++ b/src/server/api/endpoints/notes/favorites/create.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import Favorite from '../../../../../models/favorite';
 import Note from '../../../../../models/note';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -25,17 +26,31 @@ export const meta = {
 				'en-US': 'Target note ID.'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '6dd26674-e060-4816-909a-45ba3f4da458'
+		},
+
+		alreadyFavorited: {
+			message: 'The note has already been marked as a favorite.',
+			code: 'ALREADY_FAVORITED',
+			id: 'a402c12b-34dd-41d2-97d8-4d2ffd96a1a6'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Get favoritee
 	const note = await Note.findOne({
 		_id: ps.noteId
 	});
 
 	if (note === null) {
-		return rej('note not found');
+		throw new ApiError(meta.errors.noSuchNote);
 	}
 
 	// if already favorited
@@ -45,7 +60,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist !== null) {
-		return rej('already favorited');
+		throw new ApiError(meta.errors.alreadyFavorited);
 	}
 
 	// Create favorite
@@ -55,6 +70,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		userId: user._id
 	});
 
-	// Send response
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/notes/favorites/delete.ts b/src/server/api/endpoints/notes/favorites/delete.ts
index f0b9e249f7..700eafdaf7 100644
--- a/src/server/api/endpoints/notes/favorites/delete.ts
+++ b/src/server/api/endpoints/notes/favorites/delete.ts
@@ -3,6 +3,7 @@ import ID, { transform } from '../../../../../misc/cafy-id';
 import Favorite from '../../../../../models/favorite';
 import Note from '../../../../../models/note';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -25,17 +26,31 @@ export const meta = {
 				'en-US': 'Target note ID.'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '80848a2c-398f-4343-baa9-df1d57696c56'
+		},
+
+		notFavorited: {
+			message: 'You have not marked that note a favorite.',
+			code: 'NOT_FAVORITED',
+			id: 'b625fc69-635e-45e9-86f4-dbefbef35af5'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Get favoritee
 	const note = await Note.findOne({
 		_id: ps.noteId
 	});
 
 	if (note === null) {
-		return rej('note not found');
+		throw new ApiError(meta.errors.noSuchNote);
 	}
 
 	// if already favorited
@@ -45,7 +60,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist === null) {
-		return rej('already not favorited');
+		throw new ApiError(meta.errors.notFavorited);
 	}
 
 	// Delete favorite
@@ -53,6 +68,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		_id: exist._id
 	});
 
-	// Send response
-	res();
-}));
+	return;
+});
diff --git a/src/server/api/endpoints/notes/featured.ts b/src/server/api/endpoints/notes/featured.ts
index 7a3c2b76ee..08cc677abd 100644
--- a/src/server/api/endpoints/notes/featured.ts
+++ b/src/server/api/endpoints/notes/featured.ts
@@ -23,29 +23,28 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const day = 1000 * 60 * 60 * 24 * 2;
 
 	const hideUserIds = await getHideUserIds(user);
 
-	const notes = await Note
-		.find({
-			createdAt: {
-				$gt: new Date(Date.now() - day)
-			},
-			deletedAt: null,
-			visibility: { $in: ['public', 'home'] },
-			'_user.host': null,
-			...(hideUserIds && hideUserIds.length > 0 ? { userId: { $nin: hideUserIds } } : {})
-		}, {
-			limit: ps.limit,
-			sort: {
-				score: -1
-			},
-			hint: {
-				score: -1
-			}
-		});
+	const notes = await Note.find({
+		createdAt: {
+			$gt: new Date(Date.now() - day)
+		},
+		deletedAt: null,
+		visibility: { $in: ['public', 'home'] },
+		'_user.host': null,
+		...(hideUserIds && hideUserIds.length > 0 ? { userId: { $nin: hideUserIds } } : {})
+	}, {
+		limit: ps.limit,
+		sort: {
+			score: -1
+		},
+		hint: {
+			score: -1
+		}
+	});
 
-	res(await packMany(notes, user));
-}));
+	return await packMany(notes, user);
+});
diff --git a/src/server/api/endpoints/notes/global-timeline.ts b/src/server/api/endpoints/notes/global-timeline.ts
index 11825f288f..8670f8edbb 100644
--- a/src/server/api/endpoints/notes/global-timeline.ts
+++ b/src/server/api/endpoints/notes/global-timeline.ts
@@ -3,9 +3,9 @@ import ID, { transform } from '../../../../misc/cafy-id';
 import Note from '../../../../models/note';
 import { packMany } from '../../../../models/note';
 import define from '../../define';
-import { countIf } from '../../../../prelude/array';
 import fetchMeta from '../../../../misc/fetch-meta';
 import { getHideUserIds } from '../../common/get-hide-users';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -49,22 +49,25 @@ export const meta = {
 		untilDate: {
 			validator: $.optional.num
 		},
+	},
+
+	errors: {
+		gtlDisabled: {
+			message: 'Global timeline has been disabled.',
+			code: 'GTL_DISABLED',
+			id: '0332fc13-6ab2-4427-ae80-a9fadffd1a6b'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	const meta = await fetchMeta();
-	if (meta.disableGlobalTimeline) {
+export default define(meta, async (ps, user) => {
+	const m = await fetchMeta();
+	if (m.disableGlobalTimeline) {
 		if (user == null || (!user.isAdmin && !user.isModerator)) {
-			return rej('global timeline disabled');
+			throw new ApiError(meta.errors.gtlDisabled);
 		}
 	}
 
-	// Check if only one of sinceId, untilId, sinceDate, untilDate specified
-	if (countIf(x => x != null, [ps.sinceId, ps.untilId, ps.sinceDate, ps.untilDate]) > 1) {
-		return rej('only one of sinceId, untilId, sinceDate, untilDate can be specified');
-	}
-
 	// 隠すユーザーを取得
 	const hideUserIds = await getHideUserIds(user);
 
@@ -123,11 +126,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	}
 	//#endregion
 
-	const timeline = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
+	const timeline = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
-	res(await packMany(timeline, user));
-}));
+	return await packMany(timeline, user);
+});
diff --git a/src/server/api/endpoints/notes/hybrid-timeline.ts b/src/server/api/endpoints/notes/hybrid-timeline.ts
index 77ccf1abca..f3050caeca 100644
--- a/src/server/api/endpoints/notes/hybrid-timeline.ts
+++ b/src/server/api/endpoints/notes/hybrid-timeline.ts
@@ -4,10 +4,10 @@ import Note from '../../../../models/note';
 import { getFriends } from '../../common/get-friends';
 import { packMany } from '../../../../models/note';
 import define from '../../define';
-import { countIf } from '../../../../prelude/array';
 import fetchMeta from '../../../../misc/fetch-meta';
 import activeUsersChart from '../../../../services/chart/active-users';
 import { getHideUserIds } from '../../common/get-hide-users';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -90,18 +90,21 @@ export const meta = {
 				'ja-JP': 'true にすると、ファイルが添付された投稿だけ取得します (このパラメータは廃止予定です。代わりに withFiles を使ってください。)'
 			}
 		},
+	},
+
+	errors: {
+		stlDisabled: {
+			message: 'Social timeline has been disabled.',
+			code: 'STL_DISABLED',
+			id: '620763f4-f621-4533-ab33-0577a1a3c342'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	const meta = await fetchMeta();
-	if (meta.disableLocalTimeline && !user.isAdmin && !user.isModerator) {
-		return rej('local timeline disabled');
-	}
-
-	// Check if only one of sinceId, untilId, sinceDate, untilDate specified
-	if (countIf(x => x != null, [ps.sinceId, ps.untilId, ps.sinceDate, ps.untilDate]) > 1) {
-		return rej('only one of sinceId, untilId, sinceDate, untilDate can be specified');
+export default define(meta, async (ps, user) => {
+	const m = await fetchMeta();
+	if (m.disableLocalTimeline && !user.isAdmin && !user.isModerator) {
+		throw new ApiError(meta.errors.stlDisabled);
 	}
 
 	const [followings, hideUserIds] = await Promise.all([
@@ -266,13 +269,12 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	}
 	//#endregion
 
-	const timeline = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
-
-	res(await packMany(timeline, user));
+	const timeline = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
 	activeUsersChart.update(user);
-}));
+
+	return await packMany(timeline, user);
+});
diff --git a/src/server/api/endpoints/notes/local-timeline.ts b/src/server/api/endpoints/notes/local-timeline.ts
index 34695e1bca..44328ebede 100644
--- a/src/server/api/endpoints/notes/local-timeline.ts
+++ b/src/server/api/endpoints/notes/local-timeline.ts
@@ -3,10 +3,10 @@ import ID, { transform } from '../../../../misc/cafy-id';
 import Note from '../../../../models/note';
 import { packMany } from '../../../../models/note';
 import define from '../../define';
-import { countIf } from '../../../../prelude/array';
 import fetchMeta from '../../../../misc/fetch-meta';
 import activeUsersChart from '../../../../services/chart/active-users';
 import { getHideUserIds } from '../../common/get-hide-users';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -65,22 +65,25 @@ export const meta = {
 		untilDate: {
 			validator: $.optional.num,
 		},
+	},
+
+	errors: {
+		ltlDisabled: {
+			message: 'Local timeline has been disabled.',
+			code: 'LTL_DISABLED',
+			id: '45a6eb02-7695-4393-b023-dd3be9aaaefd'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	const meta = await fetchMeta();
-	if (meta.disableLocalTimeline) {
+export default define(meta, async (ps, user) => {
+	const m = await fetchMeta();
+	if (m.disableLocalTimeline) {
 		if (user == null || (!user.isAdmin && !user.isModerator)) {
-			return rej('local timeline disabled');
+			throw new ApiError(meta.errors.ltlDisabled);
 		}
 	}
 
-	// Check if only one of sinceId, untilId, sinceDate, untilDate specified
-	if (countIf(x => x != null, [ps.sinceId, ps.untilId, ps.sinceDate, ps.untilDate]) > 1) {
-		return rej('only one of sinceId, untilId, sinceDate, untilDate can be specified');
-	}
-
 	// 隠すユーザーを取得
 	const hideUserIds = await getHideUserIds(user);
 
@@ -157,15 +160,14 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	}
 	//#endregion
 
-	const timeline = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
-
-	res(await packMany(timeline, user));
+	const timeline = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
 	if (user) {
 		activeUsersChart.update(user);
 	}
-}));
+
+	return await packMany(timeline, user);
+});
diff --git a/src/server/api/endpoints/notes/mentions.ts b/src/server/api/endpoints/notes/mentions.ts
index 3935a93599..090f184f7b 100644
--- a/src/server/api/endpoints/notes/mentions.ts
+++ b/src/server/api/endpoints/notes/mentions.ts
@@ -42,12 +42,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
+export default define(meta, async (ps, user) => {
 	// フォローを取得
 	const followings = await getFriends(user._id);
 
@@ -131,15 +126,14 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		};
 	}
 
-	const mentions = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
-
-	res(await packMany(mentions, user));
+	const mentions = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
 	for (const note of mentions) {
 		read(user._id, note._id);
 	}
-}));
+
+	return await packMany(mentions, user);
+});
diff --git a/src/server/api/endpoints/notes/polls/recommendation.ts b/src/server/api/endpoints/notes/polls/recommendation.ts
index 8e11e65296..61a1840b88 100644
--- a/src/server/api/endpoints/notes/polls/recommendation.ts
+++ b/src/server/api/endpoints/notes/polls/recommendation.ts
@@ -25,7 +25,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Get votes
 	const votes = await Vote.find({
 		userId: user._id
@@ -41,29 +41,28 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	// 隠すユーザーを取得
 	const hideUserIds = await getHideUserIds(user);
 
-	const notes = await Note
-		.find({
-			'_user.host': null,
-			_id: {
-				$nin: nin
-			},
-			userId: {
-				$ne: user._id,
-				$nin: hideUserIds
-			},
-			poll: {
-				$exists: true,
-				$ne: null
-			}
-		}, {
-			limit: ps.limit,
-			skip: ps.offset,
-			sort: {
-				_id: -1
-			}
-		});
+	const notes = await Note.find({
+		'_user.host': null,
+		_id: {
+			$nin: nin
+		},
+		userId: {
+			$ne: user._id,
+			$nin: hideUserIds
+		},
+		poll: {
+			$exists: true,
+			$ne: null
+		}
+	}, {
+		limit: ps.limit,
+		skip: ps.offset,
+		sort: {
+			_id: -1
+		}
+	});
 
-	res(await Promise.all(notes.map(note => pack(note, user, {
+	return await Promise.all(notes.map(note => pack(note, user, {
 		detail: true
-	}))));
-}));
+	})));
+});
diff --git a/src/server/api/endpoints/notes/polls/vote.ts b/src/server/api/endpoints/notes/polls/vote.ts
index 68c3898e05..fe0fffec61 100644
--- a/src/server/api/endpoints/notes/polls/vote.ts
+++ b/src/server/api/endpoints/notes/polls/vote.ts
@@ -9,6 +9,7 @@ import notify from '../../../../../services/create-notification';
 import define from '../../../define';
 import createNote from '../../../../../services/note/create';
 import User from '../../../../../models/user';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -33,24 +34,52 @@ export const meta = {
 		choice: {
 			validator: $.num
 		},
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: 'ecafbd2e-c283-4d6d-aecb-1a0a33b75396'
+		},
+
+		noPoll: {
+			message: 'The note does not attach a poll.',
+			code: 'NO_POLL',
+			id: '5f979967-52d9-4314-a911-1c673727f92f'
+		},
+
+		invalidChoice: {
+			message: 'Choice ID is invalid.',
+			code: 'INVALID_CHOICE',
+			id: 'e0cc9a04-f2e8-41e4-a5f1-4127293260cc'
+		},
+
+		alreadyVoted: {
+			message: 'You have already voted.',
+			code: 'ALREADY_VOTED',
+			id: '0963fc77-efac-419b-9424-b391608dc6d8'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Get votee
 	const note = await Note.findOne({
 		_id: ps.noteId
 	});
 
 	if (note === null) {
-		return rej('note not found');
+		throw new ApiError(meta.errors.noSuchNote);
 	}
 
 	if (note.poll == null) {
-		return rej('poll not found');
+		throw new ApiError(meta.errors.noPoll);
 	}
 
-	if (!note.poll.choices.some(x => x.id == ps.choice)) return rej('invalid choice param');
+	if (!note.poll.choices.some(x => x.id == ps.choice)) {
+		throw new ApiError(meta.errors.invalidChoice);
+	}
 
 	// if already voted
 	const exist = await Vote.findOne({
@@ -59,7 +88,7 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (exist !== null) {
-		return rej('already voted');
+		throw new ApiError(meta.errors.alreadyVoted);
 	}
 
 	// Create vote
@@ -70,9 +99,6 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		choice: ps.choice
 	});
 
-	// Send response
-	res();
-
 	const inc: any = {};
 	inc[`poll.choices.${note.poll.choices.findIndex(c => c.id == ps.choice)}.votes`] = 1;
 
@@ -132,4 +158,6 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 			visibleUsers: [ pollOwner ],
 		});
 	}
-}));
+
+	return;
+});
diff --git a/src/server/api/endpoints/notes/reactions.ts b/src/server/api/endpoints/notes/reactions.ts
index 54cbd23379..3e0656c4f8 100644
--- a/src/server/api/endpoints/notes/reactions.ts
+++ b/src/server/api/endpoints/notes/reactions.ts
@@ -1,8 +1,9 @@
 import $ from 'cafy';
 import ID, { transform } from '../../../../misc/cafy-id';
-import Note from '../../../../models/note';
 import Reaction, { pack } from '../../../../models/note-reaction';
 import define from '../../define';
+import { getValiedNote } from '../../common/getters';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -41,24 +42,23 @@ export const meta = {
 			validator: $.optional.type(ID),
 			transform: transform,
 		},
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '263fff3d-d0e1-4af4-bea7-8408059b451a'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
-	// Lookup note
-	const note = await Note.findOne({
-		_id: ps.noteId
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	if (note === null) {
-		return rej('note not found');
-	}
-
 	const query = {
 		noteId: note._id
 	} as any;
@@ -78,13 +78,11 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		};
 	}
 
-	const reactions = await Reaction
-		.find(query, {
-			limit: ps.limit,
-			skip: ps.offset,
-			sort: sort
-		});
+	const reactions = await Reaction.find(query, {
+		limit: ps.limit,
+		skip: ps.offset,
+		sort: sort
+	});
 
-	// Serialize
-	res(await Promise.all(reactions.map(reaction => pack(reaction, user))));
-}));
+	return await Promise.all(reactions.map(reaction => pack(reaction, user)));
+});
diff --git a/src/server/api/endpoints/notes/reactions/create.ts b/src/server/api/endpoints/notes/reactions/create.ts
index 2612b129d0..65232e231d 100644
--- a/src/server/api/endpoints/notes/reactions/create.ts
+++ b/src/server/api/endpoints/notes/reactions/create.ts
@@ -1,11 +1,10 @@
-import * as mongo from 'mongodb';
 import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
 import createReaction from '../../../../../services/note/reaction/create';
 import { validateReaction } from '../../../../../models/note-reaction';
 import define from '../../../define';
-import { IUser } from '../../../../../models/user';
 import { getValiedNote } from '../../../common/getters';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -34,15 +33,38 @@ export const meta = {
 				'ja-JP': 'リアクションの種類'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '033d0620-5bfe-4027-965d-980b0c85a3ea'
+		},
+
+		isMyNote: {
+			message: 'You can not react to your own notes.',
+			code: 'IS_MY_NOTE',
+			id: '7eeb9714-b047-43b5-b559-7b1b72810f53'
+		},
+
+		alreadyReacted: {
+			message: 'You are already reacting to that note.',
+			code: 'ALREADY_REACTED',
+			id: '71efcf98-86d6-4e2b-b2ad-9d032369366b'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise((res, rej) => {
-	createReactionById(user, ps.noteId, ps.reaction)
-		.then(r => res(r)).catch(e => rej(e));
-}));
-
-async function createReactionById(user: IUser, noteId: mongo.ObjectID, reaction: string) {
-	const note = await getValiedNote(noteId);
-	await createReaction(user, note, reaction);
-}
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
+	});
+	await createReaction(user, note, ps.reaction).catch(e => {
+		if (e.id === '2d8e7297-1873-4c00-8404-792c68d7bef0') throw new ApiError(meta.errors.isMyNote);
+		if (e.id === '51c42bb4-931a-456b-bff7-e5a8a70dd298') throw new ApiError(meta.errors.alreadyReacted);
+		throw e;
+	});
+	return;
+});
diff --git a/src/server/api/endpoints/notes/reactions/delete.ts b/src/server/api/endpoints/notes/reactions/delete.ts
index da3c2e3567..47e98f63e4 100644
--- a/src/server/api/endpoints/notes/reactions/delete.ts
+++ b/src/server/api/endpoints/notes/reactions/delete.ts
@@ -1,11 +1,10 @@
-import * as mongo from 'mongodb';
 import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
 import define from '../../../define';
 import * as ms from 'ms';
 import deleteReaction from '../../../../../services/note/reaction/delete';
-import { IUser } from '../../../../../models/user';
 import { getValiedNote } from '../../../common/getters';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -32,15 +31,30 @@ export const meta = {
 				'en-US': 'Target note ID'
 			}
 		},
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '764d9fce-f9f2-4a0e-92b1-6ceac9a7ad37'
+		},
+
+		notReacted: {
+			message: 'You are not reacting to that note.',
+			code: 'NOT_REACTED',
+			id: '92f4426d-4196-4125-aa5b-02943e2ec8fc'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise((res, rej) => {
-	deleteReactionById(user, ps.noteId)
-		.then(r => res(r)).catch(e => rej(e));
-}));
-
-async function deleteReactionById(user: IUser, noteId: mongo.ObjectID) {
-	const note = await getValiedNote(noteId);
-	await deleteReaction(user, note);
-}
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
+	});
+	await deleteReaction(user, note).catch(e => {
+		if (e.id === '60527ec9-b4cb-4a88-a6bd-32d3ad26817d') throw new ApiError(meta.errors.notReacted);
+		throw e;
+	});
+});
diff --git a/src/server/api/endpoints/notes/renotes.ts b/src/server/api/endpoints/notes/renotes.ts
index 531953540f..9873f1bffa 100644
--- a/src/server/api/endpoints/notes/renotes.ts
+++ b/src/server/api/endpoints/notes/renotes.ts
@@ -2,6 +2,8 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../misc/cafy-id';
 import Note, { packMany } from '../../../../models/note';
 import define from '../../define';
+import { getValiedNote } from '../../common/getters';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -35,24 +37,23 @@ export const meta = {
 			validator: $.optional.type(ID),
 			transform: transform,
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '12908022-2e21-46cd-ba6a-3edaf6093f46'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if both of sinceId and untilId is specified
-	if (ps.sinceId && ps.untilId) {
-		return rej('cannot set sinceId and untilId');
-	}
-
-	// Lookup note
-	const note = await Note.findOne({
-		_id: ps.noteId
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	if (note === null) {
-		return rej('note not found');
-	}
-
 	const sort = {
 		_id: -1
 	};
@@ -72,11 +73,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		};
 	}
 
-	const renotes = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
+	const renotes = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
-	res(await packMany(renotes, user));
-}));
+	return await packMany(renotes, user);
+});
diff --git a/src/server/api/endpoints/notes/replies.ts b/src/server/api/endpoints/notes/replies.ts
index 26e9c6c5c9..080917f6f6 100644
--- a/src/server/api/endpoints/notes/replies.ts
+++ b/src/server/api/endpoints/notes/replies.ts
@@ -35,7 +35,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const [followings, hideUserIds] = await Promise.all([
 		// フォローを取得
 		// Fetch following
@@ -85,5 +85,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		skip: ps.offset
 	});
 
-	res(await packMany(notes, user));
-}));
+	return await packMany(notes, user);
+});
diff --git a/src/server/api/endpoints/notes/search.ts b/src/server/api/endpoints/notes/search.ts
index e671e72504..3eec2e3189 100644
--- a/src/server/api/endpoints/notes/search.ts
+++ b/src/server/api/endpoints/notes/search.ts
@@ -4,7 +4,7 @@ import Note from '../../../../models/note';
 import { packMany } from '../../../../models/note';
 import es from '../../../../db/elasticsearch';
 import define from '../../define';
-import { apiLogger } from '../../logger';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -28,13 +28,21 @@ export const meta = {
 			validator: $.optional.num.min(0),
 			default: 0
 		}
+	},
+
+	errors: {
+		searchingNotAvailable: {
+			message: 'Searching not available.',
+			code: 'SEARCHING_NOT_AVAILABLE',
+			id: '7ee9c119-16a1-479f-a6fd-6fab00ed946f'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
-	if (es == null) return rej('searching not available');
+export default define(meta, async (ps, me) => {
+	if (es == null) throw new ApiError(meta.errors.searchingNotAvailable);
 
-	es.search({
+	const response = await es.search({
 		index: 'misskey',
 		type: 'note',
 		body: {
@@ -51,29 +59,24 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 				{ _doc: 'desc' }
 			]
 		}
-	}, async (error, response) => {
-		if (error) {
-			apiLogger.error(error);
-			return res(500);
-		}
-
-		if (response.hits.total === 0) {
-			return res([]);
-		}
-
-		const hits = response.hits.hits.map(hit => new mongo.ObjectID(hit._id));
-
-		// Fetch found notes
-		const notes = await Note.find({
-			_id: {
-				$in: hits
-			}
-		}, {
-				sort: {
-					_id: -1
-				}
-			});
-
-		res(await packMany(notes, me));
 	});
-}));
+
+	if (response.hits.total === 0) {
+		return [];
+	}
+
+	const hits = response.hits.hits.map(hit => new mongo.ObjectID(hit._id));
+
+	// Fetch found notes
+	const notes = await Note.find({
+		_id: {
+			$in: hits
+		}
+	}, {
+		sort: {
+			_id: -1
+		}
+	});
+
+	return await packMany(notes, me);
+});
diff --git a/src/server/api/endpoints/notes/search_by_tag.ts b/src/server/api/endpoints/notes/search_by_tag.ts
index 05b22bb9f0..a4fd1903ef 100644
--- a/src/server/api/endpoints/notes/search_by_tag.ts
+++ b/src/server/api/endpoints/notes/search_by_tag.ts
@@ -103,7 +103,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const visibleQuery = me == null ? [{
 		visibility: { $in: [ 'public', 'home' ] }
 	}] : [{
@@ -317,15 +317,13 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	}
 
 	// Search notes
-	const notes = await Note
-		.find(q, {
-			sort: {
-				_id: -1
-			},
-			limit: ps.limit,
-			skip: ps.offset
-		});
+	const notes = await Note.find(q, {
+		sort: {
+			_id: -1
+		},
+		limit: ps.limit,
+		skip: ps.offset
+	});
 
-	// Serialize
-	res(await packMany(notes, me));
-}));
+	return await packMany(notes, me);
+});
diff --git a/src/server/api/endpoints/notes/show.ts b/src/server/api/endpoints/notes/show.ts
index 41134a2202..2134fad953 100644
--- a/src/server/api/endpoints/notes/show.ts
+++ b/src/server/api/endpoints/notes/show.ts
@@ -1,7 +1,9 @@
 import $ from 'cafy';
 import ID, { transform } from '../../../../misc/cafy-id';
-import Note, { pack } from '../../../../models/note';
+import { pack } from '../../../../models/note';
 import define from '../../define';
+import { getValiedNote } from '../../common/getters';
+import { ApiError } from '../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -22,21 +24,24 @@ export const meta = {
 				'en-US': 'Target note ID.'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '24fcbfc6-2e37-42b6-8388-c29b3861a08d'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Get note
-	const note = await Note.findOne({
-		_id: ps.noteId
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	if (note === null) {
-		return rej('note not found');
-	}
-
-	// Serialize
-	res(await pack(note, user, {
+	return await pack(note, user, {
 		detail: true
-	}));
-}));
+	});
+});
diff --git a/src/server/api/endpoints/notes/state.ts b/src/server/api/endpoints/notes/state.ts
index 7519241e0b..07e35480fd 100644
--- a/src/server/api/endpoints/notes/state.ts
+++ b/src/server/api/endpoints/notes/state.ts
@@ -26,7 +26,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const [favorite, watching] = await Promise.all([
 		Favorite.count({
 			userId: user._id,
@@ -42,8 +42,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		})
 	]);
 
-	res({
+	return {
 		isFavorited: favorite !== 0,
 		isWatching: watching !== 0
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/notes/timeline.ts b/src/server/api/endpoints/notes/timeline.ts
index aff3ec8cb6..cb6900a10b 100644
--- a/src/server/api/endpoints/notes/timeline.ts
+++ b/src/server/api/endpoints/notes/timeline.ts
@@ -4,7 +4,6 @@ import Note from '../../../../models/note';
 import { getFriends } from '../../common/get-friends';
 import { packMany } from '../../../../models/note';
 import define from '../../define';
-import { countIf } from '../../../../prelude/array';
 import activeUsersChart from '../../../../services/chart/active-users';
 import { getHideUserIds } from '../../common/get-hide-users';
 
@@ -95,13 +94,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Check if only one of sinceId, untilId, sinceDate, untilDate specified
-	if (countIf(x => x != null, [ps.sinceId, ps.untilId, ps.sinceDate, ps.untilDate]) > 1) {
-		rej('only one of sinceId, untilId, sinceDate, untilDate can be specified');
-		return;
-	}
-
+export default define(meta, async (ps, user) => {
 	const [followings, hideUserIds] = await Promise.all([
 		// フォローを取得
 		// Fetch following
@@ -255,15 +248,12 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	}
 	//#endregion
 
-	// Issue query
-	const timeline = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
-
-	// Serialize
-	res(await packMany(timeline, user));
+	const timeline = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
 	activeUsersChart.update(user);
-}));
+
+	return await packMany(timeline, user);
+});
diff --git a/src/server/api/endpoints/notes/user-list-timeline.ts b/src/server/api/endpoints/notes/user-list-timeline.ts
index eaaa80c3a7..1969b924ad 100644
--- a/src/server/api/endpoints/notes/user-list-timeline.ts
+++ b/src/server/api/endpoints/notes/user-list-timeline.ts
@@ -6,6 +6,7 @@ import UserList from '../../../../models/user-list';
 import define from '../../define';
 import { getFriends } from '../../common/get-friends';
 import { getHideUserIds } from '../../common/get-hide-users';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -99,10 +100,18 @@ export const meta = {
 				'ja-JP': 'true にすると、ファイルが添付された投稿だけ取得します (このパラメータは廃止予定です。代わりに withFiles を使ってください。)'
 			}
 		},
+	},
+
+	errors: {
+		noSuchList: {
+			message: 'No such list.',
+			code: 'NO_SUCH_LIST',
+			id: '8fb1fbd5-e476-4c37-9fb0-43d55b63a2ff'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const [list, followings, hideUserIds] = await Promise.all([
 		// リストを取得
 		// Fetch the list
@@ -120,13 +129,11 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	]);
 
 	if (list == null) {
-		rej('list not found');
-		return;
+		throw new ApiError(meta.errors.noSuchList);
 	}
 
 	if (list.userIds.length == 0) {
-		res([]);
-		return;
+		return [];
 	}
 
 	//#region Construct query
@@ -274,13 +281,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	}
 	//#endregion
 
-	// Issue query
-	const timeline = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
+	const timeline = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
-	// Serialize
-	res(await packMany(timeline, user));
-}));
+	return await packMany(timeline, user);
+});
diff --git a/src/server/api/endpoints/notes/watching/create.ts b/src/server/api/endpoints/notes/watching/create.ts
index 5efe69a3b4..ebba211fc0 100644
--- a/src/server/api/endpoints/notes/watching/create.ts
+++ b/src/server/api/endpoints/notes/watching/create.ts
@@ -1,8 +1,9 @@
 import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
-import Note from '../../../../../models/note';
 import define from '../../../define';
 import watch from '../../../../../services/note/watch';
+import { getValiedNote } from '../../../common/getters';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -25,21 +26,22 @@ export const meta = {
 				'en-US': 'Target note ID.'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: 'ea0e37a6-90a3-4f58-ba6b-c328ca206fc7'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Get note
-	const note = await Note.findOne({
-		_id: ps.noteId
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	if (note === null) {
-		return rej('note not found');
-	}
-
 	await watch(user._id, note);
-
-	// Send response
-	res();
-}));
+});
diff --git a/src/server/api/endpoints/notes/watching/delete.ts b/src/server/api/endpoints/notes/watching/delete.ts
index 2d99cc8254..63354d4ab2 100644
--- a/src/server/api/endpoints/notes/watching/delete.ts
+++ b/src/server/api/endpoints/notes/watching/delete.ts
@@ -1,8 +1,9 @@
 import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
-import Note from '../../../../../models/note';
 import define from '../../../define';
 import unwatch from '../../../../../services/note/unwatch';
+import { getValiedNote } from '../../../common/getters';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	stability: 'stable',
@@ -25,21 +26,22 @@ export const meta = {
 				'en-US': 'Target note ID.'
 			}
 		}
+	},
+
+	errors: {
+		noSuchNote: {
+			message: 'No such note.',
+			code: 'NO_SUCH_NOTE',
+			id: '09b3695c-f72c-4731-a428-7cff825fc82e'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// Get note
-	const note = await Note.findOne({
-		_id: ps.noteId
+export default define(meta, async (ps, user) => {
+	const note = await getValiedNote(ps.noteId).catch(e => {
+		if (e.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
+		throw e;
 	});
 
-	if (note === null) {
-		return rej('note not found');
-	}
-
 	await unwatch(user._id, note);
-
-	// Send response
-	res();
-}));
+});
diff --git a/src/server/api/endpoints/notifications/mark_all_as_read.ts b/src/server/api/endpoints/notifications/mark_all_as_read.ts
index de5a12707b..91e10b46eb 100644
--- a/src/server/api/endpoints/notifications/mark_all_as_read.ts
+++ b/src/server/api/endpoints/notifications/mark_all_as_read.ts
@@ -14,21 +14,18 @@ export const meta = {
 	kind: 'notification-write'
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Update documents
 	await Notification.update({
 		notifieeId: user._id,
 		isRead: false
 	}, {
-			$set: {
-				isRead: true
-			}
-		}, {
-			multi: true
-		});
-
-	// Response
-	res();
+		$set: {
+			isRead: true
+		}
+	}, {
+		multi: true
+	});
 
 	// Update flag
 	User.update({ _id: user._id }, {
@@ -39,4 +36,4 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 
 	// 全ての通知を読みましたよというイベントを発行
 	publishMainStream(user._id, 'readAllNotifications');
-}));
+});
diff --git a/src/server/api/endpoints/stats.ts b/src/server/api/endpoints/stats.ts
index bb5b1a6ad5..43d7c44952 100644
--- a/src/server/api/endpoints/stats.ts
+++ b/src/server/api/endpoints/stats.ts
@@ -14,7 +14,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, () => new Promise(async (res, rej) => {
+export default define(meta, async () => {
 	const instance = await fetchMeta();
 
 	const stats: any = instance.stats;
@@ -26,5 +26,5 @@ export default define(meta, () => new Promise(async (res, rej) => {
 	const federationStats = await federationChart.getChart('hour', 1);
 	stats.instances = federationStats.instance.total[0];
 
-	res(stats);
-}));
+	return stats;
+});
diff --git a/src/server/api/endpoints/sw/register.ts b/src/server/api/endpoints/sw/register.ts
index 095c1b765d..870c13555f 100644
--- a/src/server/api/endpoints/sw/register.ts
+++ b/src/server/api/endpoints/sw/register.ts
@@ -21,7 +21,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// if already subscribed
 	const exist = await Subscription.findOne({
 		userId: user._id,
@@ -34,10 +34,10 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	const instance = await fetchMeta();
 
 	if (exist != null) {
-		return res({
+		return {
 			state: 'already-subscribed',
 			key: instance.swPublicKey
-		});
+		};
 	}
 
 	await Subscription.insert({
@@ -47,8 +47,8 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		publickey: ps.publickey
 	});
 
-	res({
+	return {
 		state: 'subscribed',
 		key: instance.swPublicKey
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/username/available.ts b/src/server/api/endpoints/username/available.ts
index a5f0b5943f..a651bc4d55 100644
--- a/src/server/api/endpoints/username/available.ts
+++ b/src/server/api/endpoints/username/available.ts
@@ -13,18 +13,16 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps) => new Promise(async (res, rej) => {
+export default define(meta, async (ps) => {
 	// Get exist
-	const exist = await User
-		.count({
-			host: null,
-			usernameLower: ps.username.toLowerCase()
-		}, {
-			limit: 1
-		});
-
-	// Reply
-	res({
-		available: exist === 0
+	const exist = await User.count({
+		host: null,
+		usernameLower: ps.username.toLowerCase()
+	}, {
+		limit: 1
 	});
-}));
+
+	return {
+		available: exist === 0
+	};
+});
diff --git a/src/server/api/endpoints/users.ts b/src/server/api/endpoints/users.ts
index fd8cc6413e..f7e7a10011 100644
--- a/src/server/api/endpoints/users.ts
+++ b/src/server/api/endpoints/users.ts
@@ -86,7 +86,7 @@ const sort: any = { // < https://github.com/Microsoft/TypeScript/issues/1863
 	[fallback]: { _id: -1 }
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const hideUserIds = await getHideUserIds(me);
 
 	const users = await User
@@ -102,5 +102,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			skip: ps.offset
 		});
 
-	res(await Promise.all(users.map(user => pack(user, me, { detail: true }))));
-}));
+	return await Promise.all(users.map(user => pack(user, me, { detail: true })));
+});
diff --git a/src/server/api/endpoints/users/followers.ts b/src/server/api/endpoints/users/followers.ts
index 2f7f1af6a5..cb5b047626 100644
--- a/src/server/api/endpoints/users/followers.ts
+++ b/src/server/api/endpoints/users/followers.ts
@@ -5,6 +5,7 @@ import Following from '../../../../models/following';
 import { pack } from '../../../../models/user';
 import { getFriendIds } from '../../common/get-friends';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -47,10 +48,18 @@ export const meta = {
 			validator: $.optional.bool,
 			default: false,
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '27fa5435-88ab-43de-9360-387de88727cd'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const q: any = ps.userId != null
 		? { _id: ps.userId }
 		: { usernameLower: ps.username.toLowerCase(), host: ps.host };
@@ -58,10 +67,9 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	const user = await User.findOne(q);
 
 	if (user === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
-	// Construct query
 	const query = {
 		followeeId: user._id
 	} as any;
@@ -98,8 +106,8 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 
 	const users = await Promise.all(following.map(f => pack(f.followerId, me, { detail: true })));
 
-	res({
+	return {
 		users: users,
 		next: inStock ? following[following.length - 1]._id : null,
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/users/following.ts b/src/server/api/endpoints/users/following.ts
index 1485a63f24..04abe5f4b3 100644
--- a/src/server/api/endpoints/users/following.ts
+++ b/src/server/api/endpoints/users/following.ts
@@ -5,6 +5,7 @@ import Following from '../../../../models/following';
 import { pack } from '../../../../models/user';
 import { getFriendIds } from '../../common/get-friends';
 import define from '../../define';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -47,10 +48,18 @@ export const meta = {
 			validator: $.optional.bool,
 			default: false,
 		}
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '63e4aba4-4156-4e53-be25-c9559e42d71b'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const q: any = ps.userId != null
 		? { _id: ps.userId }
 		: { usernameLower: ps.username.toLowerCase(), host: ps.host };
@@ -58,10 +67,9 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	const user = await User.findOne(q);
 
 	if (user === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
-	// Construct query
 	const query = {
 		followerId: user._id
 	} as any;
@@ -98,8 +106,8 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 
 	const users = await Promise.all(following.map(f => pack(f.followeeId, me, { detail: true })));
 
-	res({
+	return {
 		users: users,
 		next: inStock ? following[following.length - 1]._id : null,
-	});
-}));
+	};
+});
diff --git a/src/server/api/endpoints/users/get_frequently_replied_users.ts b/src/server/api/endpoints/users/get_frequently_replied_users.ts
index e897fe8db2..b20d1ef69e 100644
--- a/src/server/api/endpoints/users/get_frequently_replied_users.ts
+++ b/src/server/api/endpoints/users/get_frequently_replied_users.ts
@@ -5,6 +5,7 @@ import User, { pack } from '../../../../models/user';
 import define from '../../define';
 import { maximum } from '../../../../prelude/array';
 import { getHideUserIds } from '../../common/get-hide-users';
+import { ApiError } from '../../error';
 
 export const meta = {
 	requireCredential: false,
@@ -23,10 +24,18 @@ export const meta = {
 			validator: $.optional.num.range(1, 100),
 			default: 10
 		},
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: 'e6965129-7b2a-40a4-bae2-cd84cd434822'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	// Lookup user
 	const user = await User.findOne({
 		_id: ps.userId
@@ -37,7 +46,7 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	});
 
 	if (user === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Fetch recent notes
@@ -60,7 +69,7 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 
 	// 投稿が少なかったら中断
 	if (recentNotes.length === 0) {
-		return res([]);
+		return [];
 	}
 
 	const hideUserIds = await getHideUserIds(me);
@@ -106,5 +115,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		weight: repliedUsers[user] / peak
 	})));
 
-	res(repliesObj);
-}));
+	return repliesObj;
+});
diff --git a/src/server/api/endpoints/users/lists/create.ts b/src/server/api/endpoints/users/lists/create.ts
index d93cf13d94..a3d91b6c25 100644
--- a/src/server/api/endpoints/users/lists/create.ts
+++ b/src/server/api/endpoints/users/lists/create.ts
@@ -19,8 +19,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
-	// insert
+export default define(meta, async (ps, user) => {
 	const userList = await UserList.insert({
 		createdAt: new Date(),
 		userId: user._id,
@@ -28,6 +27,5 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 		userIds: []
 	});
 
-	// Response
-	res(await pack(userList));
-}));
+	return await pack(userList);
+});
diff --git a/src/server/api/endpoints/users/lists/delete.ts b/src/server/api/endpoints/users/lists/delete.ts
index 8d297198c9..6aaf4701d4 100644
--- a/src/server/api/endpoints/users/lists/delete.ts
+++ b/src/server/api/endpoints/users/lists/delete.ts
@@ -2,6 +2,7 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
 import UserList from '../../../../../models/user-list';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -22,22 +23,28 @@ export const meta = {
 				'en-US': 'ID of target user list'
 			}
 		}
+	},
+
+	errors: {
+		noSuchList: {
+			message: 'No such list.',
+			code: 'NO_SUCH_LIST',
+			id: '78436795-db79-42f5-b1e2-55ea2cf19166'
+		}
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	const userList = await UserList.findOne({
 		_id: ps.listId,
 		userId: user._id
 	});
 
 	if (userList == null) {
-		return rej('list not found');
+		throw new ApiError(meta.errors.noSuchList);
 	}
 
 	await UserList.remove({
 		_id: userList._id
 	});
-
-	res();
-}));
+});
diff --git a/src/server/api/endpoints/users/lists/list.ts b/src/server/api/endpoints/users/lists/list.ts
index 8f9775e19b..5bd662878d 100644
--- a/src/server/api/endpoints/users/lists/list.ts
+++ b/src/server/api/endpoints/users/lists/list.ts
@@ -11,11 +11,10 @@ export const meta = {
 	kind: 'account-read'
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
-	// Fetch lists
+export default define(meta, async (ps, me) => {
 	const userLists = await UserList.find({
 		userId: me._id,
 	});
 
-	res(await Promise.all(userLists.map(x => pack(x))));
-}));
+	return await Promise.all(userLists.map(x => pack(x)));
+});
diff --git a/src/server/api/endpoints/users/lists/pull.ts b/src/server/api/endpoints/users/lists/pull.ts
index 86eaa1dd8d..416c1b4b2d 100644
--- a/src/server/api/endpoints/users/lists/pull.ts
+++ b/src/server/api/endpoints/users/lists/pull.ts
@@ -4,6 +4,7 @@ import UserList from '../../../../../models/user-list';
 import User, { pack as packUser } from '../../../../../models/user';
 import { publishUserListStream } from '../../../../../services/stream';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -29,10 +30,24 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		},
+	},
+
+	errors: {
+		noSuchList: {
+			message: 'No such list.',
+			code: 'NO_SUCH_LIST',
+			id: '7f44670e-ab16-43b8-b4c1-ccd2ee89cc02'
+		},
+
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '588e7f72-c744-4a61-b180-d354e912bda2'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	// Fetch the list
 	const userList = await UserList.findOne({
 		_id: ps.listId,
@@ -40,7 +55,7 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	});
 
 	if (userList == null) {
-		return rej('list not found');
+		throw new ApiError(meta.errors.noSuchList);
 	}
 
 	// Fetch the user
@@ -49,7 +64,7 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	// Pull the user
@@ -59,7 +74,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-
 	publishUserListStream(userList._id, 'userRemoved', await packUser(user));
-}));
+});
diff --git a/src/server/api/endpoints/users/lists/push.ts b/src/server/api/endpoints/users/lists/push.ts
index 6e2dbed518..90dd2aa045 100644
--- a/src/server/api/endpoints/users/lists/push.ts
+++ b/src/server/api/endpoints/users/lists/push.ts
@@ -7,6 +7,7 @@ import { renderActivity } from '../../../../../remote/activitypub/renderer';
 import renderFollow from '../../../../../remote/activitypub/renderer/follow';
 import { deliver } from '../../../../../queue';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -32,10 +33,30 @@ export const meta = {
 				'en-US': 'Target user ID'
 			}
 		},
+	},
+
+	errors: {
+		noSuchList: {
+			message: 'No such list.',
+			code: 'NO_SUCH_LIST',
+			id: '2214501d-ac96-4049-b717-91e42272a711'
+		},
+
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: 'a89abd3d-f0bc-4cce-beb1-2f446f4f1e6a'
+		},
+
+		alreadyAdded: {
+			message: 'That user has already been added to that list.',
+			code: 'ALREADY_ADDED',
+			id: '1de7c884-1595-49e9-857e-61f12f4d4fc5'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	// Fetch the list
 	const userList = await UserList.findOne({
 		_id: ps.listId,
@@ -43,7 +64,7 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	});
 
 	if (userList == null) {
-		return rej('list not found');
+		throw new ApiError(meta.errors.noSuchList);
 	}
 
 	// Fetch the user
@@ -52,11 +73,11 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	});
 
 	if (user == null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	if (userList.userIds.map(id => id.toHexString()).includes(user._id.toHexString())) {
-		return rej('the user already added');
+		throw new ApiError(meta.errors.alreadyAdded);
 	}
 
 	// Push the user
@@ -66,8 +87,6 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		}
 	});
 
-	res();
-
 	publishUserListStream(userList._id, 'userAdded', await packUser(user));
 
 	// このインスタンス内にこのリモートユーザーをフォローしているユーザーがいなくても投稿を受け取るためにダミーのユーザーがフォローしたということにする
@@ -76,4 +95,4 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		const content = renderActivity(renderFollow(proxy, user));
 		deliver(proxy, content, user.inbox);
 	}
-}));
+});
diff --git a/src/server/api/endpoints/users/lists/show.ts b/src/server/api/endpoints/users/lists/show.ts
index c508659a15..3bd8ce6573 100644
--- a/src/server/api/endpoints/users/lists/show.ts
+++ b/src/server/api/endpoints/users/lists/show.ts
@@ -2,6 +2,7 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
 import UserList, { pack } from '../../../../../models/user-list';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -18,10 +19,18 @@ export const meta = {
 			validator: $.type(ID),
 			transform: transform,
 		},
+	},
+
+	errors: {
+		noSuchList: {
+			message: 'No such list.',
+			code: 'NO_SUCH_LIST',
+			id: '7bc05c21-1d7a-41ae-88f1-66820f4dc686'
+		},
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	// Fetch the list
 	const userList = await UserList.findOne({
 		_id: ps.listId,
@@ -29,8 +38,8 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	});
 
 	if (userList == null) {
-		return rej('list not found');
+		throw new ApiError(meta.errors.noSuchList);
 	}
 
-	res(await pack(userList));
-}));
+	return await pack(userList);
+});
diff --git a/src/server/api/endpoints/users/lists/update.ts b/src/server/api/endpoints/users/lists/update.ts
index 79a7da5658..842ae189ee 100644
--- a/src/server/api/endpoints/users/lists/update.ts
+++ b/src/server/api/endpoints/users/lists/update.ts
@@ -2,6 +2,7 @@ import $ from 'cafy';
 import ID, { transform } from '../../../../../misc/cafy-id';
 import UserList, { pack } from '../../../../../models/user-list';
 import define from '../../../define';
+import { ApiError } from '../../../error';
 
 export const meta = {
 	desc: {
@@ -30,10 +31,18 @@ export const meta = {
 				'en-US': 'name of this user list'
 			}
 		}
+	},
+
+	errors: {
+		noSuchList: {
+			message: 'No such list.',
+			code: 'NO_SUCH_LIST',
+			id: '796666fe-3dff-4d39-becb-8a5932c1d5b7'
+		},
 	}
 };
 
-export default define(meta, (ps, user) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, user) => {
 	// Fetch the list
 	const userList = await UserList.findOne({
 		_id: ps.listId,
@@ -41,16 +50,14 @@ export default define(meta, (ps, user) => new Promise(async (res, rej) => {
 	});
 
 	if (userList == null) {
-		return rej('list not found');
+		throw new ApiError(meta.errors.noSuchList);
 	}
 
-	// update
 	await UserList.update({ _id: userList._id }, {
 		$set: {
 			title: ps.title
 		}
 	});
 
-	// Response
-	res(await pack(userList._id));
-}));
+	return await pack(userList._id);
+});
diff --git a/src/server/api/endpoints/users/notes.ts b/src/server/api/endpoints/users/notes.ts
index 5c776e48e2..98d67e865a 100644
--- a/src/server/api/endpoints/users/notes.ts
+++ b/src/server/api/endpoints/users/notes.ts
@@ -1,11 +1,10 @@
 import $ from 'cafy';
 import ID, { transform } from '../../../../misc/cafy-id';
-import getHostLower from '../../common/get-host-lower';
 import Note, { packMany } from '../../../../models/note';
 import User from '../../../../models/user';
 import define from '../../define';
-import { countIf } from '../../../../prelude/array';
 import Following from '../../../../models/following';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -14,7 +13,7 @@ export const meta = {
 
 	params: {
 		userId: {
-			validator: $.optional.type(ID),
+			validator: $.type(ID),
 			transform: transform,
 			desc: {
 				'ja-JP': '対象のユーザーのID',
@@ -22,17 +21,6 @@ export const meta = {
 			}
 		},
 
-		username: {
-			validator: $.optional.str,
-			desc: {
-				'ja-JP': 'ユーザー名'
-			}
-		},
-
-		host: {
-			validator: $.optional.nullable.str,
-		},
-
 		includeReplies: {
 			validator: $.optional.bool,
 			default: true,
@@ -134,32 +122,27 @@ export const meta = {
 				'ja-JP': 'true にすると、NSFW指定されたファイルを除外します(fileTypeが指定されている場合のみ有効)'
 			}
 		},
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '27e494ba-2ac2-48e8-893b-10d4d8c2387b'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
-	if (ps.userId === undefined && ps.username === undefined) {
-		return rej('userId or username is required');
-	}
-
-	// Check if only one of sinceId, untilId, sinceDate, untilDate specified
-	if (countIf(x => x != null, [ps.sinceId, ps.untilId, ps.sinceDate, ps.untilDate]) > 1) {
-		throw 'only one of sinceId, untilId, sinceDate, untilDate can be specified';
-	}
-
-	const q = ps.userId != null
-		? { _id: ps.userId }
-		: { usernameLower: ps.username.toLowerCase(), host: getHostLower(ps.host) } ;
-
+export default define(meta, async (ps, me) => {
 	// Lookup user
-	const user = await User.findOne(q, {
+	const user = await User.findOne({ _id: ps.userId }, {
 		fields: {
 			_id: true
 		}
 	});
 
 	if (user === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	const isFollowing = me == null ? false : ((await Following.findOne({
@@ -259,13 +242,10 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 	}
 	//#endregion
 
-	// Issue query
-	const notes = await Note
-		.find(query, {
-			limit: ps.limit,
-			sort: sort
-		});
+	const notes = await Note.find(query, {
+		limit: ps.limit,
+		sort: sort
+	});
 
-	// Serialize
-	res(await packMany(notes, me));
-}));
+	return await packMany(notes, me);
+});
diff --git a/src/server/api/endpoints/users/recommendation.ts b/src/server/api/endpoints/users/recommendation.ts
index e9f0107716..dc37bc56ba 100644
--- a/src/server/api/endpoints/users/recommendation.ts
+++ b/src/server/api/endpoints/users/recommendation.ts
@@ -32,7 +32,7 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const instance = await fetchMeta();
 
 	if (instance.enableExternalUserRecommendation) {
@@ -48,7 +48,7 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			.replace('{{limit}}', limit.toString())
 			.replace('{{offset}}', offset.toString());
 
-		request({
+		const users = await request({
 			url: url,
 			proxy: config.proxy,
 			timeout: timeout,
@@ -56,37 +56,36 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			followRedirect: true,
 			followAllRedirects: true
 		})
-			.then(body => convertUsers(body, me))
-			.then(packed => res(packed))
-			.catch(e => rej(e));
+		.then(body => convertUsers(body, me));
+
+		return users;
 	} else {
 		// ID list of the user itself and other users who the user follows
 		const followingIds = await getFriendIds(me._id);
 
-	// 隠すユーザーを取得
-	const hideUserIds = await getHideUserIds(me);
+		// 隠すユーザーを取得
+		const hideUserIds = await getHideUserIds(me);
 
-		const users = await User
-			.find({
-				_id: {
-					$nin: followingIds.concat(hideUserIds)
-				},
-				isLocked: { $ne: true },
-				updatedAt: {
-					$gte: new Date(Date.now() - ms('7days'))
-				},
-				host: null
-			}, {
-				limit: ps.limit,
-				skip: ps.offset,
-				sort: {
-					followersCount: -1
-				}
-			});
+		const users = await User.find({
+			_id: {
+				$nin: followingIds.concat(hideUserIds)
+			},
+			isLocked: { $ne: true },
+			updatedAt: {
+				$gte: new Date(Date.now() - ms('7days'))
+			},
+			host: null
+		}, {
+			limit: ps.limit,
+			skip: ps.offset,
+			sort: {
+				followersCount: -1
+			}
+		});
 
-		res(await Promise.all(users.map(user => pack(user, me, { detail: true }))));
+		return await Promise.all(users.map(user => pack(user, me, { detail: true })));
 	}
-}));
+});
 
 type IRecommendUser = {
 	name: string;
diff --git a/src/server/api/endpoints/users/relation.ts b/src/server/api/endpoints/users/relation.ts
index 43d5e70640..5b7b4d8e4d 100644
--- a/src/server/api/endpoints/users/relation.ts
+++ b/src/server/api/endpoints/users/relation.ts
@@ -21,10 +21,10 @@ export const meta = {
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const ids = Array.isArray(ps.userId) ? ps.userId : [ps.userId];
 
 	const relations = await Promise.all(ids.map(id => getRelation(me._id, id)));
 
-	res(Array.isArray(ps.userId) ? relations : relations[0]);
-}));
+	return Array.isArray(ps.userId) ? relations : relations[0];
+});
diff --git a/src/server/api/endpoints/users/report-abuse.ts b/src/server/api/endpoints/users/report-abuse.ts
index c592e5cfd4..32a2393493 100644
--- a/src/server/api/endpoints/users/report-abuse.ts
+++ b/src/server/api/endpoints/users/report-abuse.ts
@@ -4,6 +4,7 @@ import define from '../../define';
 import User from '../../../../models/user';
 import AbuseUserReport from '../../../../models/abuse-user-report';
 import { publishAdminStream } from '../../../../services/stream';
+import { ApiError } from '../../error';
 
 export const meta = {
 	desc: {
@@ -28,25 +29,45 @@ export const meta = {
 				'ja-JP': '迷惑行為の詳細'
 			}
 		},
+	},
+
+	errors: {
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '1acefcb5-0959-43fd-9685-b48305736cb5'
+		},
+
+		cannotReportYourself: {
+			message: 'Cannot report yourself.',
+			code: 'CANNOT_REPORT_YOURSELF',
+			id: '1e13149e-b1e8-43cf-902e-c01dbfcb202f'
+		},
+
+		cannotReportAdmin: {
+			message: 'Cannot report the admin.',
+			code: 'CANNOT_REPORT_THE_ADMIN',
+			id: '35e166f5-05fb-4f87-a2d5-adb42676d48f'
+		}
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	// Lookup user
 	const user = await User.findOne({
 		_id: ps.userId
 	});
 
 	if (user === null) {
-		return rej('user not found');
+		throw new ApiError(meta.errors.noSuchUser);
 	}
 
 	if (user._id.equals(me._id)) {
-		return rej('cannot report yourself');
+		throw new ApiError(meta.errors.cannotReportYourself);
 	}
 
 	if (user.isAdmin) {
-		return rej('cannot report admin');
+		throw new ApiError(meta.errors.cannotReportAdmin);
 	}
 
 	const report = await AbuseUserReport.insert({
@@ -65,6 +86,7 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 				isModerator: true
 			}]
 		});
+
 		for (const moderator of moderators) {
 			publishAdminStream(moderator._id, 'newAbuseUserReport', {
 				id: report._id,
@@ -74,6 +96,4 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			});
 		}
 	}, 1);
-
-	res();
-}));
+});
diff --git a/src/server/api/endpoints/users/search.ts b/src/server/api/endpoints/users/search.ts
index 5dc1e4aeab..6fd390f283 100644
--- a/src/server/api/endpoints/users/search.ts
+++ b/src/server/api/endpoints/users/search.ts
@@ -52,7 +52,7 @@ export const meta = {
 	},
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	const isUsername = validateUsername(ps.query.replace('@', ''), !ps.localOnly);
 
 	let users: IUser[] = [];
@@ -80,5 +80,5 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		}
 	}
 
-	res(await Promise.all(users.map(user => pack(user, me, { detail: ps.detail }))));
-}));
+	return await Promise.all(users.map(user => pack(user, me, { detail: ps.detail })));
+});
diff --git a/src/server/api/endpoints/users/show.ts b/src/server/api/endpoints/users/show.ts
index 025598b8ff..4f870b8b92 100644
--- a/src/server/api/endpoints/users/show.ts
+++ b/src/server/api/endpoints/users/show.ts
@@ -4,6 +4,7 @@ import User, { pack, isRemoteUser } from '../../../../models/user';
 import resolveRemoteUser from '../../../../remote/resolve-user';
 import define from '../../define';
 import { apiLogger } from '../../logger';
+import { ApiError } from '../../error';
 
 const cursorOption = { fields: { data: false } };
 
@@ -39,10 +40,25 @@ export const meta = {
 		host: {
 			validator: $.optional.nullable.str
 		}
+	},
+
+	errors: {
+		failedToResolveRemoteUser: {
+			message: 'Failed to resolve remote user.',
+			code: 'FAILED_TO_RESOLVE_REMOTE_USER',
+			id: 'ef7b9be4-9cba-4e6f-ab41-90ed171c7d3c',
+			kind: 'server' as 'server'
+		},
+
+		noSuchUser: {
+			message: 'No such user.',
+			code: 'NO_SUCH_USER',
+			id: '4362f8dc-731f-4ad8-a694-be5a88922a24'
+		},
 	}
 };
 
-export default define(meta, (ps, me) => new Promise(async (res, rej) => {
+export default define(meta, async (ps, me) => {
 	let user;
 
 	if (ps.userIds) {
@@ -52,18 +68,16 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 			}
 		});
 
-		res(await Promise.all(users.map(u => pack(u, me, {
+		return await Promise.all(users.map(u => pack(u, me, {
 			detail: true
-		}))));
+		})));
 	} else {
 		// Lookup user
 		if (typeof ps.host === 'string') {
-			try {
-				user = await resolveRemoteUser(ps.username, ps.host, cursorOption);
-			} catch (e) {
+			user = await resolveRemoteUser(ps.username, ps.host, cursorOption).catch(e => {
 				apiLogger.warn(`failed to resolve remote user: ${e}`);
-				return rej('failed to resolve remote user');
-			}
+				throw new ApiError(meta.errors.failedToResolveRemoteUser);
+			});
 		} else {
 			const q: any = ps.userId != null
 				? { _id: ps.userId }
@@ -73,18 +87,18 @@ export default define(meta, (ps, me) => new Promise(async (res, rej) => {
 		}
 
 		if (user === null) {
-			return rej('user not found');
+			throw new ApiError(meta.errors.noSuchUser);
 		}
 
-		// Send response
-		res(await pack(user, me, {
-			detail: true
-		}));
-
+		// ユーザー情報更新
 		if (isRemoteUser(user)) {
 			if (user.lastFetchedAt == null || Date.now() - user.lastFetchedAt.getTime() > 1000 * 60 * 60 * 24) {
 				resolveRemoteUser(ps.username, ps.host, { }, true);
 			}
 		}
+
+		return await pack(user, me, {
+			detail: true
+		});
 	}
-}));
+});
diff --git a/src/server/api/error.ts b/src/server/api/error.ts
new file mode 100644
index 0000000000..6b5c44cac2
--- /dev/null
+++ b/src/server/api/error.ts
@@ -0,0 +1,23 @@
+export class ApiError extends Error {
+	public message: string;
+	public code: string;
+	public id: string;
+	public kind: string;
+	public info?: any;
+
+	constructor(e?: { message: string, code: string, id: string, kind?: 'client' | 'server' }, info?: any) {
+		if (e == null) e = {
+			message: 'Internal error occurred. Please contact us if the error persists.',
+			code: 'INTERNAL_ERROR',
+			id: '5d37dbcb-891e-41ca-a3d6-e690c97775ac',
+			kind: 'server'
+		};
+
+		super(e.message);
+		this.message = e.message;
+		this.code = e.code;
+		this.id = e.id;
+		this.kind = e.kind || 'client';
+		this.info = info;
+	}
+}
diff --git a/src/services/following/create.ts b/src/services/following/create.ts
index 5a92e4103a..38f86fbf7d 100644
--- a/src/services/following/create.ts
+++ b/src/services/following/create.ts
@@ -15,6 +15,7 @@ import Instance from '../../models/instance';
 import instanceChart from '../../services/chart/instance';
 import Logger from '../../misc/logger';
 import FollowRequest from '../../models/follow-request';
+import { IdentifiableError } from '../../misc/identifiable-error';
 
 const logger = new Logger('following/create');
 
@@ -142,8 +143,8 @@ export default async function(follower: IUser, followee: IUser, requestId?: stri
 		});
 	} else {
 		// それ以外は単純に例外
-		if (blocking != null) throw new Error('blocking');
-		if (blocked != null) throw new Error('blocked');
+		if (blocking != null) throw new IdentifiableError('710e8fb0-b8c3-4922-be49-d5d93d8e6a6e', 'blocking');
+		if (blocked != null) throw new IdentifiableError('3338392a-f764-498d-8855-db939dcf8c48', 'blocked');
 	}
 
 	// フォロー対象が鍵アカウントである or
diff --git a/src/services/following/requests/cancel.ts b/src/services/following/requests/cancel.ts
index 375c14d5e1..af4cca85fe 100644
--- a/src/services/following/requests/cancel.ts
+++ b/src/services/following/requests/cancel.ts
@@ -5,6 +5,7 @@ import renderFollow from '../../../remote/activitypub/renderer/follow';
 import renderUndo from '../../../remote/activitypub/renderer/undo';
 import { deliver } from '../../../queue';
 import { publishMainStream } from '../../stream';
+import { IdentifiableError } from '../../../misc/identifiable-error';
 
 export default async function(followee: IUser, follower: IUser) {
 	if (isRemoteUser(followee)) {
@@ -18,7 +19,7 @@ export default async function(followee: IUser, follower: IUser) {
 	});
 
 	if (request == null) {
-		throw 'request not found';
+		throw new IdentifiableError('17447091-ce07-46dd-b331-c1fd4f15b1e7', 'request not found');
 	}
 
 	await FollowRequest.remove({
diff --git a/src/services/i/pin.ts b/src/services/i/pin.ts
index c48c1838ab..4d0ae3c149 100644
--- a/src/services/i/pin.ts
+++ b/src/services/i/pin.ts
@@ -7,6 +7,7 @@ import renderAdd from '../../remote/activitypub/renderer/add';
 import renderRemove from '../../remote/activitypub/renderer/remove';
 import { renderActivity } from '../../remote/activitypub/renderer';
 import { deliver } from '../../queue';
+import { IdentifiableError } from '../../misc/identifiable-error';
 
 /**
  * 指定した投稿をピン留めします
@@ -21,7 +22,7 @@ export async function addPinned(user: IUser, noteId: mongo.ObjectID) {
 	});
 
 	if (note === null) {
-		throw new Error('note not found');
+		throw new IdentifiableError('70c4e51f-5bea-449c-a030-53bee3cce202', 'No such note.');
 	}
 
 	let pinnedNoteIds = user.pinnedNoteIds || [];
@@ -35,11 +36,11 @@ export async function addPinned(user: IUser, noteId: mongo.ObjectID) {
 	//#endregion
 
 	if (pinnedNoteIds.length >= 5) {
-		throw new Error('cannot pin more notes');
+		throw new IdentifiableError('15a018eb-58e5-4da1-93be-330fcc5e4e1a', 'You can not pin notes any more.');
 	}
 
 	if (pinnedNoteIds.some(id => id.equals(note._id))) {
-		throw new Error('already exists');
+		throw new IdentifiableError('23f0cf4e-59a3-4276-a91d-61a5891c1514', 'That note has already been pinned.');
 	}
 
 	pinnedNoteIds.unshift(note._id);
@@ -69,7 +70,7 @@ export async function removePinned(user: IUser, noteId: mongo.ObjectID) {
 	});
 
 	if (note === null) {
-		throw new Error('note not found');
+		throw new IdentifiableError('b302d4cf-c050-400a-bbb3-be208681f40c', 'No such note.');
 	}
 
 	const pinnedNoteIds = (user.pinnedNoteIds || []).filter(id => !id.equals(note._id));
diff --git a/src/services/note/polls/vote.ts b/src/services/note/polls/vote.ts
index 115b071b45..e154f33b7b 100644
--- a/src/services/note/polls/vote.ts
+++ b/src/services/note/polls/vote.ts
@@ -27,7 +27,6 @@ export default (user: IUser, note: INote, choice: number) => new Promise(async (
 		choice: choice
 	});
 
-	// Send response
 	res();
 
 	const inc: any = {};
diff --git a/src/services/note/reaction/create.ts b/src/services/note/reaction/create.ts
index cf72927642..5897df2c97 100644
--- a/src/services/note/reaction/create.ts
+++ b/src/services/note/reaction/create.ts
@@ -9,31 +9,28 @@ import renderLike from '../../../remote/activitypub/renderer/like';
 import { deliver } from '../../../queue';
 import { renderActivity } from '../../../remote/activitypub/renderer';
 import perUserReactionsChart from '../../../services/chart/per-user-reactions';
+import { IdentifiableError } from '../../../misc/identifiable-error';
 
-export default async (user: IUser, note: INote, reaction: string) => new Promise(async (res, rej) => {
+export default async (user: IUser, note: INote, reaction: string) => {
 	// Myself
 	if (note.userId.equals(user._id)) {
-		return rej('cannot react to my note');
+		throw new IdentifiableError('2d8e7297-1873-4c00-8404-792c68d7bef0', 'cannot react to my note');
 	}
 
 	// Create reaction
-	try {
-		await NoteReaction.insert({
-			createdAt: new Date(),
-			noteId: note._id,
-			userId: user._id,
-			reaction
-		});
-	} catch (e) {
+	await NoteReaction.insert({
+		createdAt: new Date(),
+		noteId: note._id,
+		userId: user._id,
+		reaction
+	}).catch(e => {
 		// duplicate key error
 		if (e.code === 11000) {
-			return rej('already reacted');
+			throw new IdentifiableError('51c42bb4-931a-456b-bff7-e5a8a70dd298', 'already reacted');
 		}
 
-		return rej('something happened');
-	}
-
-	res();
+		throw e;
+	});
 
 	// Increment reactions count
 	await Note.update({ _id: note._id }, {
@@ -89,4 +86,6 @@ export default async (user: IUser, note: INote, reaction: string) => new Promise
 		deliver(user, content, note._user.inbox);
 	}
 	//#endregion
-});
+
+	return;
+};
diff --git a/src/services/note/reaction/delete.ts b/src/services/note/reaction/delete.ts
index ee3a9e13d8..9735d4ec01 100644
--- a/src/services/note/reaction/delete.ts
+++ b/src/services/note/reaction/delete.ts
@@ -6,8 +6,9 @@ import renderLike from '../../../remote/activitypub/renderer/like';
 import renderUndo from '../../../remote/activitypub/renderer/undo';
 import { renderActivity } from '../../../remote/activitypub/renderer';
 import { deliver } from '../../../queue';
+import { IdentifiableError } from '../../../misc/identifiable-error';
 
-export default async (user: IUser, note: INote) => new Promise(async (res, rej) => {
+export default async (user: IUser, note: INote) => {
 	// if already unreacted
 	const exist = await Reaction.findOne({
 		noteId: note._id,
@@ -16,7 +17,7 @@ export default async (user: IUser, note: INote) => new Promise(async (res, rej)
 	});
 
 	if (exist === null) {
-		return rej('never reacted');
+		throw new IdentifiableError('60527ec9-b4cb-4a88-a6bd-32d3ad26817d', 'not reacted');
 	}
 
 	// Delete reaction
@@ -24,8 +25,6 @@ export default async (user: IUser, note: INote) => new Promise(async (res, rej)
 		_id: exist._id
 	});
 
-	res();
-
 	const dec: any = {};
 	dec[`reactionCounts.${exist.reaction}`] = -1;
 
@@ -46,4 +45,6 @@ export default async (user: IUser, note: INote) => new Promise(async (res, rej)
 		deliver(user, content, note._user.inbox);
 	}
 	//#endregion
-});
+
+	return;
+};