diff --git a/backend/src/activitypub/actors/index.ts b/backend/src/activitypub/actors/index.ts
index 1043267..5166f09 100644
--- a/backend/src/activitypub/actors/index.ts
+++ b/backend/src/activitypub/actors/index.ts
@@ -1,6 +1,7 @@
 import { defaultImages } from 'wildebeest/config/accounts'
 import { generateUserKey } from 'wildebeest/backend/src/utils/key-ops'
 import { type APObject, sanitizeContent, sanitizeName } from '../objects'
+import { addPeer } from 'wildebeest/backend/src/activitypub/peers'
 
 const PERSON = 'Person'
 const isTesting = typeof jest !== 'undefined'
@@ -112,6 +113,12 @@ export async function getAndCache(url: URL, db: D1Database): Promise<Actor> {
 	if (!success) {
 		throw new Error('SQL error: ' + error)
 	}
+
+	// Add peer
+	{
+		const domain = actor.id.host
+		await addPeer(db, domain)
+	}
 	return actor
 }
 
diff --git a/backend/src/activitypub/objects/index.ts b/backend/src/activitypub/objects/index.ts
index 4cf6511..316eff4 100644
--- a/backend/src/activitypub/objects/index.ts
+++ b/backend/src/activitypub/objects/index.ts
@@ -1,4 +1,5 @@
 import type { UUID } from 'wildebeest/backend/src/types'
+import { addPeer } from 'wildebeest/backend/src/activitypub/peers'
 
 export const originalActorIdSymbol = Symbol()
 export const originalObjectIdSymbol = Symbol()
@@ -118,6 +119,12 @@ export async function cacheObject(
 		)
 		.first()
 
+	// Add peer
+	{
+		const domain = originalObjectId.host
+		await addPeer(db, domain)
+	}
+
 	{
 		const properties = JSON.parse(row.properties)
 		const object = {
diff --git a/backend/src/activitypub/peers.ts b/backend/src/activitypub/peers.ts
new file mode 100644
index 0000000..44c6433
--- /dev/null
+++ b/backend/src/activitypub/peers.ts
@@ -0,0 +1,20 @@
+import { getResultsField } from 'wildebeest/backend/src/mastodon/utils'
+
+export async function getPeers(db: D1Database): Promise<Array<String>> {
+	const query = `SELECT domain FROM peers `
+	const statement = db.prepare(query)
+
+	return getResultsField(statement, 'domain')
+}
+
+export async function addPeer(db: D1Database, domain: string): Promise<void> {
+	const query = `
+		INSERT OR IGNORE INTO peers (domain)
+		VALUES (?)
+	`
+
+	const out = await db.prepare(query).bind(domain).run()
+	if (!out.success) {
+		throw new Error('SQL error: ' + out.error)
+	}
+}
diff --git a/backend/test/activitypub.spec.ts b/backend/test/activitypub.spec.ts
index 28cba26..584a796 100644
--- a/backend/test/activitypub.spec.ts
+++ b/backend/test/activitypub.spec.ts
@@ -2,6 +2,7 @@ import { makeDB, isUrlValid } from './utils'
 import { MessageType } from 'wildebeest/backend/src/types/queue'
 import type { JWK } from 'wildebeest/backend/src/webpush/jwk'
 import { createPerson } from 'wildebeest/backend/src/activitypub/actors'
+import * as actors from 'wildebeest/backend/src/activitypub/actors'
 import { createPrivateNote, createPublicNote } from 'wildebeest/backend/src/activitypub/objects/note'
 import { addObjectInOutbox } from 'wildebeest/backend/src/activitypub/actors/outbox'
 import { strict as assert } from 'node:assert/strict'
@@ -128,6 +129,38 @@ describe('ActivityPub', () => {
 		})
 	})
 
+	describe('Actors', () => {
+		test('getAndCache adds peer', async () => {
+			const actorId = new URL('https://example.com/user/foo')
+
+			globalThis.fetch = async (input: RequestInfo) => {
+				if (input.toString() === actorId.toString()) {
+					return new Response(
+						JSON.stringify({
+							id: actorId,
+							type: 'Person',
+							preferredUsername: 'sven',
+							name: 'sven ssss',
+
+							icon: { url: 'icon.jpg' },
+							image: { url: 'image.jpg' },
+						})
+					)
+				}
+
+				throw new Error(`unexpected request to "${input}"`)
+			}
+
+			const db = await makeDB()
+
+			await actors.getAndCache(actorId, db)
+
+			const { results } = (await db.prepare('SELECT domain from peers').all()) as any
+			assert.equal(results.length, 1)
+			assert.equal(results[0].domain, 'example.com')
+		})
+	})
+
 	describe('Objects', () => {
 		test('cacheObject deduplicates object', async () => {
 			const db = await makeDB()
@@ -159,6 +192,19 @@ describe('ActivityPub', () => {
 			assert.equal(result.count, 1)
 		})
 
+		test('cacheObject adds peer', async () => {
+			const db = await makeDB()
+			const properties = { type: 'Note', a: 1, b: 2 }
+			const actor = await createPerson(domain, db, userKEK, 'a@cloudflare.com')
+			const originalObjectId = new URL('https://example.com/object1')
+
+			await cacheObject(domain, db, properties, actor.id, originalObjectId, false)
+
+			const { results } = (await db.prepare('SELECT domain from peers').all()) as any
+			assert.equal(results.length, 1)
+			assert.equal(results[0].domain, 'example.com')
+		})
+
 		test('serve unknown object', async () => {
 			const db = await makeDB()
 			const res = await ap_objects.handleRequest(domain, db, 'unknown id')
diff --git a/backend/test/mastodon/instance.spec.ts b/backend/test/mastodon/instance.spec.ts
new file mode 100644
index 0000000..be13158
--- /dev/null
+++ b/backend/test/mastodon/instance.spec.ts
@@ -0,0 +1,22 @@
+import { addPeer } from 'wildebeest/backend/src/activitypub/peers'
+import { strict as assert } from 'node:assert/strict'
+import * as peers from 'wildebeest/functions/api/v1/instance/peers'
+import { makeDB } from '../utils'
+
+describe('Mastodon APIs', () => {
+	describe('instance', () => {
+		test('returns peers', async () => {
+			const db = await makeDB()
+			await addPeer(db, 'a')
+			await addPeer(db, 'b')
+
+			const res = await peers.handleRequest(db)
+			assert.equal(res.status, 200)
+
+			const data = await res.json<Array<string>>()
+			assert.equal(data.length, 2)
+			assert.equal(data[0], 'a')
+			assert.equal(data[1], 'b')
+		})
+	})
+})
diff --git a/functions/api/v1/instance/peers.ts b/functions/api/v1/instance/peers.ts
new file mode 100644
index 0000000..dde8c11
--- /dev/null
+++ b/functions/api/v1/instance/peers.ts
@@ -0,0 +1,16 @@
+import { cors } from 'wildebeest/backend/src/utils/cors'
+import type { Env } from 'wildebeest/backend/src/types/env'
+import { getPeers } from 'wildebeest/backend/src/activitypub/peers'
+
+export const onRequest: PagesFunction<Env, any> = async ({ env }) => {
+	return handleRequest(env.DATABASE)
+}
+
+export async function handleRequest(db: D1Database): Promise<Response> {
+	const headers = {
+		...cors(),
+		'content-type': 'application/json; charset=utf-8',
+	}
+	const peers = await getPeers(db)
+	return new Response(JSON.stringify(peers), { headers })
+}
diff --git a/migrations/0003_add_peers.sql b/migrations/0003_add_peers.sql
new file mode 100644
index 0000000..61c5298
--- /dev/null
+++ b/migrations/0003_add_peers.sql
@@ -0,0 +1,5 @@
+-- Migration number: 0003 	 2023-02-02T15:03:27.478Z
+
+CREATE TABLE IF NOT EXISTS peers (
+  domain TEXT NOT NULL
+);