diff --git a/src/remote/activitypub/renderer/index.ts b/src/remote/activitypub/renderer/index.ts
index efce8ebadae3..cfdc07cdab88 100644
--- a/src/remote/activitypub/renderer/index.ts
+++ b/src/remote/activitypub/renderer/index.ts
@@ -4,48 +4,156 @@ import { IActivity } from '../type';
 import { LdSignature } from '../misc/ld-signature';
 import { ILocalUser } from '../../../models/user';
 
-export const renderActivity = (x: any): IActivity | null => {
+const references = [
+	'https://www.w3.org/ns/activitystreams',
+	'https://w3id.org/security/v1',
+];
+
+// namespaces (null means already defined in references)
+const nss: Record<string, string | null> = {
+	as: null,	// defined in 'https://www.w3.org/ns/activitystreams'
+	vcard: null,	// defined in 'https://www.w3.org/ns/activitystreams'
+	sec: null,	// defined in 'https://w3id.org/security/v1'
+	// :
+
+	// Some extra or vendor namespaces
+	toot: 'http://joinmastodon.org/ns#',	// Mastodon
+	schema: 'http://schema.org#',
+	misskey: 'https://misskey-hub.net/ns#',
+	fedibird: 'http://fedibird.com/ns#',
+};
+
+// Definitions! (required ns => key => value)
+const defs: Record<string, Record<string, string | object>> = {
+	sec: {
+		Key: 'sec:Key',
+	},
+	as: {	// Not defined by the activitystreams, but defined in Mastodon.
+		manuallyApprovesFollowers: 'as:manuallyApprovesFollowers',
+		sensitive: 'as:sensitive',
+		Hashtag: 'as:Hashtag',
+	},
+	toot: {
+		Emoji: 'toot:Emoji',
+		featured: 'toot:featured',
+		discoverable: 'toot:discoverable',
+		indexable: 'toot:indexable',
+	},
+	schema: {
+		PropertyValue: 'schema:PropertyValue',
+		value: 'schema:value',
+	},
+	misskey: {
+		_misskey_content: 'misskey:_misskey_content',
+		_misskey_quote: 'misskey:_misskey_quote',
+		_misskey_reaction: 'misskey:_misskey_reaction',
+		_misskey_votes: 'misskey:_misskey_votes',
+		isCat: 'misskey:isCat',
+	},
+	fedibird: {
+		quoteUri: 'fedibird:quoteUri',
+		searchableBy: { '@id': 'fedibird:searchableBy', '@type': '@id' },
+	},
+};
+
+// flatten defs for processing
+type Def = {
+	/*** Key, eg: '_misskey_content' */
+	key: string;
+	/*** Resolved value, eg: 'misskey:_misskey_content' */
+	value: string | Object;
+	/*** Required namaspace, eg: 'misskey' */
+	ns: string;
+};
+
+const fdefs = new Map<string, Def>();
+
+for (const [ns, keyval] of Object.entries(defs)) {
+	for (const [key, value] of Object.entries(keyval)) {
+		fdefs.set(key, { key, ns, value })
+	}
+}
+
+// builds
+const buildContext = (extraKeys: string[]) => {
+	const extraNss = new Map<string, string>();
+	const extraDefs = new Map<string, string | object>();
+
+	for (const key of extraKeys) {
+		const def = fdefs.get(key);
+		if (def == null) {
+			console.warn(`JSON-LD: key=${key} is not in defs, bug?`);
+		} else {
+			const nsValue = nss[def.ns];
+			if (nsValue === undefined) {
+				console.warn(`JSON-LD: ns=${key} is not in nss, bug?`);
+			} else if (nsValue === null) {
+				// alredy in imported one, so safety ignore it
+			} else {
+				extraNss.set(def.ns, nsValue)
+			}
+
+			extraDefs.set(key, def.value)
+		}
+	}
+
+	return [
+		...references,
+		{
+			...Object.fromEntries(extraNss),
+			...Object.fromEntries(extraDefs),
+		}
+	];
+};
+
+const prebuildContexts = {
+	Any: buildContext(Array.from(fdefs.keys())),
+	Actor: buildContext([
+		'Key',
+		'manuallyApprovesFollowers',
+		'sensitive',
+		'Hashtag',
+		'Emoji',
+		'featured',
+		'discoverable',
+		'indexable',
+		'PropertyValue',
+		'value',
+		'isCat',
+		'searchableBy'
+	]),
+	Like: buildContext([
+		'Emoji',
+		'_misskey_reaction',
+	]),
+	Note: buildContext([
+		'sensitive',
+		'Hashtag',
+		'Emoji',
+		'_misskey_content',
+		'_misskey_quote',
+		'_misskey_votes',
+		'quoteUri',
+	]),
+};
+
+console.log('prebuildContexts', prebuildContexts);
+
+export const renderActivity = (x: any, p?: 'Actor' | 'Like' | 'Note' | 'Any'): IActivity | null => {
 	if (x == null) return null;
 
 	if (x !== null && typeof x === 'object' && x.id == null) {
 		x.id = `${config.url}/${uuid()}`;
 	}
 
+	const context =
+		p === 'Actor' ? prebuildContexts.Actor :
+		p === 'Like' ? prebuildContexts.Like :
+		p === 'Note' ? prebuildContexts.Note :
+		prebuildContexts.Any;
+
 	return Object.assign({
-		'@context': [
-			'https://www.w3.org/ns/activitystreams',
-			'https://w3id.org/security/v1',
-			{
-				Key: 'sec:Key',
-				// as non-standards
-				manuallyApprovesFollowers: 'as:manuallyApprovesFollowers',
-				sensitive: 'as:sensitive',
-				Hashtag: 'as:Hashtag',
-				// Mastodon
-				toot: 'http://joinmastodon.org/ns#',
-				Emoji: 'toot:Emoji',
-				featured: 'toot:featured',
-				discoverable: 'toot:discoverable',
-				indexable: 'toot:indexable',
-				// schema
-				schema: 'http://schema.org#',
-				PropertyValue: 'schema:PropertyValue',
-				value: 'schema:value',
-				// Misskey
-				misskey: 'https://misskey-hub.net/ns#',
-				'_misskey_content': 'misskey:_misskey_content',
-				'_misskey_quote': 'misskey:_misskey_quote',
-				'_misskey_reaction': 'misskey:_misskey_reaction',
-				'_misskey_votes': 'misskey:_misskey_votes',
-				'isCat': 'misskey:isCat',
-				// vcard
-				vcard: 'http://www.w3.org/2006/vcard/ns#',
-				// Fedibird
-				fedibird: 'http://fedibird.com/ns#',
-				quoteUri: 'fedibird:quoteUri',
-				searchableBy: { '@id': 'fedibird:searchableBy', '@type': '@id' },
-			}
-		]
+		'@context': context
 	}, x);
 };
 
diff --git a/src/server/activitypub.ts b/src/server/activitypub.ts
index 42174d4bae6f..7c083bc0c04c 100644
--- a/src/server/activitypub.ts
+++ b/src/server/activitypub.ts
@@ -481,7 +481,7 @@ router.get('/likes/:like', async ctx => {
 		return;
 	}
 
-	ctx.body = renderActivity(await renderLike(reaction, note));
+	ctx.body = renderActivity(await renderLike(reaction, note), 'Like');
 	ctx.set('Cache-Control', 'public, max-age=180');
 	setResponseType(ctx);
 });
diff --git a/src/services/note/reaction/create.ts b/src/services/note/reaction/create.ts
index 0f74c4ab48da..89de4ff6e6d5 100644
--- a/src/services/note/reaction/create.ts
+++ b/src/services/note/reaction/create.ts
@@ -102,7 +102,7 @@ export default async (user: IUser, note: INote, reaction?: string, dislike = fal
 
 	//#region 配信
 	if (isLocalUser(user) && !note.localOnly && !user.noFederation) {
-		const content = renderActivity(await renderLike(inserted, note), user);
+		const content = renderActivity(await renderLike(inserted, note), 'Like');
 
 		const dm = new DeliverManager(user, content)
 
diff --git a/src/services/note/reaction/delete.ts b/src/services/note/reaction/delete.ts
index 743623b3dead..818d696f49f2 100644
--- a/src/services/note/reaction/delete.ts
+++ b/src/services/note/reaction/delete.ts
@@ -65,7 +65,7 @@ export default async (user: IUser, note: INote) => {
 
 	//#region 配信
 	if (isLocalUser(user) && !note.localOnly && !user.noFederation) {
-		const content = renderActivity(renderUndo(await renderLike(exist, note), user), user);
+		const content = renderActivity(renderUndo(await renderLike(exist, note), user), 'Like');
 		if (isRemoteUser(note._user)) deliverToUser(user, content, note._user);
 		deliverToFollowers(user, content, true);
 		//deliverToRelays(user, content);