diff --git a/packages/backend/src/server/api/call.ts b/packages/backend/src/server/api/call.ts
index 9458d15fe..c20443ca6 100644
--- a/packages/backend/src/server/api/call.ts
+++ b/packages/backend/src/server/api/call.ts
@@ -5,6 +5,7 @@ import { AccessToken } from '@/models/entities/access-token.js';
 import { getIpHash } from '@/misc/get-ip-hash.js';
 import { limiter } from './limiter.js';
 import endpoints, { IEndpointMeta } from './endpoints.js';
+import compatibility from './compatibility.js';
 import { ApiError } from './error.js';
 import { apiLogger } from './logger.js';
 import { AccessToken } from '@/models/entities/access-token.js';
@@ -20,7 +21,8 @@ export default async (endpoint: string, user: CacheableLocalUser | null | undefi
 	const isSecure = user != null && token == null;
 	const isModerator = user != null && (user.isModerator || user.isAdmin);
 
-	const ep = endpoints.find(e => e.name === endpoint);
+	const ep = endpoints.find(e => e.name === endpoint) ||
+		compatibility.find(e => e.name === endpoint);
 
 	if (ep == null) {
 		throw new ApiError({
diff --git a/packages/backend/src/server/api/compatibility.ts b/packages/backend/src/server/api/compatibility.ts
new file mode 100644
index 000000000..2f22cf718
--- /dev/null
+++ b/packages/backend/src/server/api/compatibility.ts
@@ -0,0 +1,20 @@
+import { IEndpoint } from './endpoints';
+
+import * as cp___instanceInfo from './endpoints/compatibility/instance-info.js';
+import * as cp___customEmojis from './endpoints/compatibility/custom-emojis.js';
+
+const cps = [
+	['v1/instance', cp___instanceInfo],
+	['v1/custom_emojis', cp___customEmojis],
+];
+
+const compatibility: IEndpoint[] = cps.map(([name, cp]) => {
+	return {
+		name: name,
+		exec: cp.default,
+		meta: cp.meta || {},
+		params: cp.paramDef,
+	} as IEndpoint;
+});
+
+export default compatibility;
diff --git a/packages/backend/src/server/api/endpoints/compatibility/custom-emojis.ts b/packages/backend/src/server/api/endpoints/compatibility/custom-emojis.ts
new file mode 100644
index 000000000..42969cff9
--- /dev/null
+++ b/packages/backend/src/server/api/endpoints/compatibility/custom-emojis.ts
@@ -0,0 +1,38 @@
+import { Emojis } from '@/models/index.js';
+import { Emoji } from '@/models/entities/emoji.js';
+import { IsNull, In } from 'typeorm';
+import { FILE_TYPE_BROWSERSAFE } from '@/const.js';
+import define from '../../define.js';
+
+export const meta = {
+	requireCredential: false,
+	requireCredentialPrivateMode: true,
+	allowGet: true,
+
+	tags: ['meta'],
+} as const;
+
+export const paramDef = {
+	type: 'object',
+	properties: {},
+	required: [],
+} as const;
+
+// eslint-disable-next-line import/no-default-export
+export default define(meta, paramDef, async () => {
+	const now = Date.now();
+	const emojis: Emoji[] = await Emojis.find({
+		where: { host: IsNull(), type: In(FILE_TYPE_BROWSERSAFE) },
+		select: ['name', 'originalUrl', 'publicUrl', 'category'],
+	});
+
+	const emojiList = emojis.map(emoji => ({
+		shortcode: emoji.name,
+		url: emoji.originalUrl,
+		static_url: emoji.publicUrl,
+		visible_in_picker: true,
+		category: emoji.category,
+	}));
+
+	return emojiList;
+});
diff --git a/packages/backend/src/server/api/endpoints/compatibility/instance-info.ts b/packages/backend/src/server/api/endpoints/compatibility/instance-info.ts
new file mode 100644
index 000000000..825119120
--- /dev/null
+++ b/packages/backend/src/server/api/endpoints/compatibility/instance-info.ts
@@ -0,0 +1,226 @@
+import * as mfm from 'mfm-js';
+import { toHtml } from '@/mfm/to-html.js';
+import config from '@/config/index.js';
+import { fetchMeta } from '@/misc/fetch-meta.js';
+import { Users, Notes, Instances, UserProfiles, Emojis, DriveFiles } from '@/models/index.js';
+import { Emoji } from '@/models/entities/emoji.js';
+import { User } from '@/models/entities/user.js';
+import { IsNull, In } from 'typeorm';
+import { MAX_NOTE_TEXT_LENGTH, FILE_TYPE_BROWSERSAFE } from '@/const.js';
+import define from '../../define.js';
+
+export const meta = {
+	requireCredential: false,
+	requireCredentialPrivateMode: true,
+	allowGet: true,
+
+	tags: ['meta'],
+} as const;
+
+export const paramDef = {
+	type: 'object',
+	properties: {},
+	required: [],
+} as const;
+
+// eslint-disable-next-line import/no-default-export
+export default define(meta, paramDef, async () => {
+	const now = Date.now();
+	const [
+		meta,
+		total,
+		localPosts,
+		instanceCount,
+		firstAdmin,
+		emojis,
+	] = await Promise.all([
+		fetchMeta(true),
+		Users.count({ where: { host: IsNull() } }),
+		Notes.count({ where: { userHost: IsNull(), replyId: IsNull() } }),
+		Instances.count(),
+		Users.findOne({
+			where: { host: IsNull(), isAdmin: true, isDeleted: false, isBot: false },
+			order: { id: 'ASC' },
+		}),
+		Emojis.find({
+			where: { host: IsNull(), type: In(FILE_TYPE_BROWSERSAFE) },
+			select: ['id', 'name', 'originalUrl', 'publicUrl'],
+		}).then(l =>
+			l.reduce((a, e) =>
+				{
+					a[e.name] = e
+					return a
+				},
+				{} as Record<string, Emoji>
+			)
+		),
+	]);
+
+	let descSplit = splitN(meta.description, '\n', 2);
+	let shortDesc = markup(descSplit.length > 0 ? descSplit[0]: '');
+	let longDesc = markup(meta.description ?? '');
+
+	return {
+			"uri": config.hostname,
+			"title": meta.name,
+			"short_description": shortDesc,
+			"description": longDesc,
+			"email": meta.maintainerEmail,
+			"version": config.version,
+			"urls": {
+				"streaming_api": `wss://${config.host}`
+			},
+			"stats": {
+				"user_count": total,
+				"status_count": localPosts,
+				"domain_count": instanceCount
+			},
+			"thumbnail": meta.logoImageUrl,
+			"languages": meta.langs,
+			"registrations": !meta.disableRegistration,
+			"approval_required": false,
+			"invites_enabled": false,
+			"configuration": {
+				"accounts": {
+					"max_featured_tags": 16
+				},
+				"statuses": {
+					"max_characters": MAX_NOTE_TEXT_LENGTH,
+					"max_media_attachments": 16,
+					"characters_reserved_per_url": 0
+				},
+				"media_attachments": {
+					"supported_mime_types": FILE_TYPE_BROWSERSAFE,
+					"image_size_limit": 10485760,
+					"image_matrix_limit": 16777216,
+					"video_size_limit": 41943040,
+					"video_frame_rate_limit": 60,
+					"video_matrix_limit": 2304000
+				},
+				"polls": {
+					"max_options": 10,
+					"max_characters_per_option": 50,
+					"min_expiration": 15,
+					"max_expiration": -1
+				}
+			},
+			"contact_account": await getContact(firstAdmin, emojis),
+			"rules": []
+	};
+});
+
+const splitN = (
+	s: string | null,
+	split: string,
+	n: number
+): string[] => {
+	const ret: string[] = [];
+	if (s == null) return ret;
+	if (s === '') {
+		ret.push(s);
+		return ret;
+	}
+
+	let start = 0;
+	let pos = s.indexOf(split);
+	if (pos === -1) {
+		ret.push(s);
+		return ret;
+	}
+
+	for (let i = 0; i < n - 1; i++) {
+		ret.push(s.substring(start, pos));
+		start = pos + split.length;
+		pos = s.indexOf(split, start);
+		if (pos === -1) break;
+	}
+	ret.push(s.substring(start));
+
+	return ret;
+};
+
+type ContactType = {
+	id: string;
+	username: string;
+	acct: string;
+	display_name: string;
+	note?: string;
+	noindex?: boolean;
+	fields?: {
+		name: string;
+		value: string;
+		verified_at:string | null;
+	}[];
+	locked: boolean;
+	bot: boolean;
+	created_at: string;
+	url: string;
+	followers_count: number;
+	following_count: number;
+	statuses_count: number;
+	last_status_at?: string;
+	emojis: any;
+} | null;
+
+const getContact = async (
+	user: User | null,
+	emojis: Record<string, Emoji>
+): Promise<ContactType> => {
+	if (!user) return null;
+
+	let contact: ContactType = {
+		id: user.id,
+		username: user.username,
+		acct: user.username,
+		display_name: user.name ?? user.username,
+		locked: user.isLocked,
+		bot: user.isBot,
+		created_at: user.createdAt.toISOString(),
+		url: `${config.url}/@${user.username}`,
+		followers_count: user.followersCount,
+		following_count: user.followingCount,
+		statuses_count: user.notesCount,
+		last_status_at: user.lastActiveDate?.toISOString(),
+		emojis: emojis ? user.emojis.map(e => ({
+			shortcode: e,
+			static_url: `${config.url}/files/${emojis[e].publicUrl}`,
+			url: `${config.url}/files/${emojis[e].publicUrl}`,
+			visible_in_picker: true,
+		})) : [],
+	};
+
+	const [profile] = await Promise.all([
+		UserProfiles.findOne({ where: { userId: user.id }}),
+		loadDriveFiles(contact, 'avatar', user.avatarId),
+		loadDriveFiles(contact, 'header', user.bannerId),
+	]);
+
+	if (!profile) {
+		return contact;
+	}
+
+	contact = {
+		...contact,
+		note: markup(profile.description ?? ''),
+		noindex: profile.noCrawle,
+		fields: profile.fields.map(f => ({
+			name: f.name,
+			value: f.value,
+			verified_at: null,
+		}))
+	};
+
+	return contact;
+}
+
+const loadDriveFiles = async (contact: any, key: string, fileId: string | null) => {
+	if (fileId) {
+		const file = await DriveFiles.findOneBy({ id: fileId });
+		if (file) {
+			contact[key] = file.webpublicUrl ?? file.url;
+			contact[`${key}_static`] = contact[key];
+		}
+	}
+}
+
+const markup = (text: string): string => toHtml(mfm.parse(text)) ?? '';
diff --git a/packages/backend/src/server/api/index.ts b/packages/backend/src/server/api/index.ts
index 83ece51f5..37bcfffec 100644
--- a/packages/backend/src/server/api/index.ts
+++ b/packages/backend/src/server/api/index.ts
@@ -7,10 +7,10 @@ import Router from '@koa/router';
 import multer from '@koa/multer';
 import bodyParser from 'koa-bodyparser';
 import cors from '@koa/cors';
-
 import { Instances, AccessTokens, Users } from '@/models/index.js';
 import config from '@/config/index.js';
 import endpoints from './endpoints.js';
+import compatibility from './compatibility.js';
 import handler from './api-handler.js';
 import signup from './private/signup.js';
 import signin from './private/signin.js';
@@ -34,7 +34,10 @@ app.use(async (ctx, next) => {
 
 app.use(bodyParser({
 	// リクエストが multipart/form-data でない限りはJSONだと見なす
-	detectJSON: ctx => !ctx.is('multipart/form-data'),
+	detectJSON: ctx => !(
+		ctx.is('multipart/form-data') ||
+		ctx.is('application/x-www-form-urlencoded')
+	)
 }));
 
 // Init multer instance
@@ -52,7 +55,7 @@ const router = new Router();
 /**
  * Register endpoint handlers
  */
-for (const endpoint of endpoints) {
+for (const endpoint of [...endpoints, ...compatibility]) {
 	if (endpoint.meta.requireFile) {
 		router.post(`/${endpoint.name}`, upload.single('file'), handler.bind(null, endpoint));
 	} else {