diff --git a/src/schemas/activitypub.ts b/src/schemas/activitypub.ts
new file mode 100644
index 0000000..04fac39
--- /dev/null
+++ b/src/schemas/activitypub.ts
@@ -0,0 +1,323 @@
+import { z } from '@/deps.ts';
+
+const apId = z.string().url();
+const recipients = z.array(z.string()).catch([]);
+const published = () => z.string().datetime().catch(new Date().toISOString());
+
+/** Validates individual items in an array, dropping any that aren't valid. */
+function filteredArray<T extends z.ZodTypeAny>(schema: T) {
+  return z.any().array()
+    .transform((arr) => (
+      arr.map((item) => {
+        const parsed = schema.safeParse(item);
+        return parsed.success ? parsed.data : undefined;
+      }).filter((item): item is z.infer<T> => Boolean(item))
+    ));
+}
+
+const imageSchema = z.object({
+  type: z.literal('Image').catch('Image'),
+  url: z.string().url(),
+});
+
+const attachmentSchema = z.object({
+  type: z.literal('Document').catch('Document'),
+  mediaType: z.string().optional().catch(undefined),
+  url: z.string().url(),
+});
+
+const mentionSchema = z.object({
+  type: z.literal('Mention'),
+  href: z.string().url(),
+  name: z.string().optional().catch(undefined),
+});
+
+const hashtagSchema = z.object({
+  type: z.literal('Hashtag'),
+  href: z.string().url(),
+  name: z.string(),
+});
+
+const emojiSchema = z.object({
+  type: z.literal('Emoji'),
+  icon: imageSchema,
+  name: z.string(),
+});
+
+const tagSchema = z.discriminatedUnion('type', [
+  mentionSchema,
+  hashtagSchema,
+  emojiSchema,
+]);
+
+const propertyValueSchema = z.object({
+  type: z.literal('PropertyValue'),
+  name: z.string(),
+  value: z.string(),
+  verified_at: z.string().nullish(),
+});
+
+/** https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-fffd.md */
+const proxySchema = z.object({
+  protocol: z.string().url(),
+  proxied: z.string(),
+  authoritative: z.boolean().optional().catch(undefined),
+});
+
+const personSchema = z.object({
+  type: z.literal('Person'),
+  id: apId,
+  icon: imageSchema.optional().catch(undefined),
+  image: imageSchema.optional().catch(undefined),
+  name: z.string().catch(''),
+  preferredUsername: z.string(),
+  inbox: apId,
+  followers: apId.optional().catch(undefined),
+  following: apId.optional().catch(undefined),
+  outbox: apId.optional().catch(undefined),
+  summary: z.string().catch(''),
+  attachment: filteredArray(propertyValueSchema).catch([]),
+  tag: filteredArray(emojiSchema).catch([]),
+  endpoints: z.object({
+    sharedInbox: apId.optional(),
+  }).optional().catch({}),
+  publicKey: z.object({
+    id: apId,
+    owner: apId,
+    publicKeyPem: z.string(),
+  }).optional().catch(undefined),
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const applicationSchema = personSchema.merge(z.object({ type: z.literal('Application') }));
+const groupSchema = personSchema.merge(z.object({ type: z.literal('Group') }));
+const organizationSchema = personSchema.merge(z.object({ type: z.literal('Organization') }));
+const serviceSchema = personSchema.merge(z.object({ type: z.literal('Service') }));
+
+const actorSchema = z.discriminatedUnion('type', [
+  personSchema,
+  applicationSchema,
+  groupSchema,
+  organizationSchema,
+  serviceSchema,
+]);
+
+const noteSchema = z.object({
+  type: z.literal('Note'),
+  id: apId,
+  to: recipients,
+  cc: recipients,
+  content: z.string(),
+  attachment: z.array(attachmentSchema).optional().catch(undefined),
+  tag: filteredArray(tagSchema).catch([]),
+  inReplyTo: apId.optional().catch(undefined),
+  attributedTo: apId,
+  published: published(),
+  sensitive: z.boolean().optional().catch(undefined),
+  summary: z.string().nullish().catch(undefined),
+  quoteUrl: apId.optional().catch(undefined),
+  source: z.object({
+    content: z.string(),
+    mediaType: z.literal('text/markdown'),
+  }).optional().catch(undefined),
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const flexibleNoteSchema = noteSchema.extend({
+  quoteURL: apId.optional().catch(undefined),
+  quoteUri: apId.optional().catch(undefined),
+  _misskey_quote: apId.optional().catch(undefined),
+}).transform((note) => {
+  const { quoteUrl, quoteUri, quoteURL, _misskey_quote, ...rest } = note;
+  return {
+    quoteUrl: quoteUrl || quoteUri || quoteURL || _misskey_quote,
+    ...rest,
+  };
+});
+
+// https://github.com/colinhacks/zod/discussions/2100#discussioncomment-5109781
+const objectSchema = z.union([
+  flexibleNoteSchema,
+  personSchema,
+  applicationSchema,
+  groupSchema,
+  organizationSchema,
+  serviceSchema,
+]).pipe(
+  z.discriminatedUnion('type', [
+    noteSchema,
+    personSchema,
+    applicationSchema,
+    groupSchema,
+    organizationSchema,
+    serviceSchema,
+  ]),
+);
+
+const createNoteSchema = z.object({
+  type: z.literal('Create'),
+  id: apId,
+  to: recipients,
+  cc: recipients,
+  actor: apId,
+  object: noteSchema,
+  published: published(),
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const announceNoteSchema = z.object({
+  type: z.literal('Announce'),
+  id: apId,
+  to: recipients,
+  cc: recipients,
+  actor: apId,
+  object: apId.or(noteSchema),
+  published: published(),
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const followSchema = z.object({
+  type: z.literal('Follow'),
+  id: apId,
+  to: recipients,
+  cc: recipients,
+  actor: apId,
+  object: apId,
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const acceptSchema = z.object({
+  type: z.literal('Accept'),
+  id: apId,
+  actor: apId,
+  to: recipients,
+  cc: recipients,
+  object: apId.or(followSchema),
+});
+
+const likeSchema = z.object({
+  type: z.literal('Like'),
+  id: apId,
+  actor: apId,
+  object: apId,
+  to: recipients,
+  cc: recipients,
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const emojiReactSchema = z.object({
+  type: z.literal('EmojiReact'),
+  id: apId,
+  actor: apId,
+  object: apId,
+  content: z.string().refine((v) => /\p{Extended_Pictographic}/u.test(v)),
+  to: recipients,
+  cc: recipients,
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const deleteSchema = z.object({
+  type: z.literal('Delete'),
+  id: apId,
+  actor: apId,
+  object: apId,
+  to: recipients,
+  cc: recipients,
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const updateActorSchema = z.object({
+  type: z.literal('Update'),
+  id: apId,
+  actor: apId,
+  to: recipients,
+  cc: recipients,
+  object: actorSchema,
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+/**
+ * A custom Zap activity type we made up, based on:
+ * https://github.com/nostr-protocol/nips/blob/master/57.md
+ */
+const zapSchema = z.object({
+  type: z.literal('Zap'),
+  id: apId,
+  actor: apId,
+  object: apId,
+  to: recipients,
+  cc: recipients,
+  proxyOf: z.array(proxySchema).optional().catch(undefined),
+});
+
+const activitySchema = z.discriminatedUnion('type', [
+  followSchema,
+  acceptSchema,
+  createNoteSchema,
+  announceNoteSchema,
+  updateActorSchema,
+  likeSchema,
+  emojiReactSchema,
+  deleteSchema,
+  zapSchema,
+]).refine((activity) => {
+  const ids: string[] = [activity.id];
+
+  if (activity.type === 'Create') {
+    ids.push(
+      activity.object.id,
+      activity.object.attributedTo,
+    );
+  }
+
+  if (activity.type === 'Update') {
+    ids.push(activity.object.id);
+  }
+
+  const { origin: actorOrigin } = new URL(activity.actor);
+
+  // Object containment
+  return ids.every((id) => {
+    const { origin: idOrigin } = new URL(id);
+    return idOrigin === actorOrigin;
+  });
+});
+
+type Activity = z.infer<typeof activitySchema>;
+type CreateNote = z.infer<typeof createNoteSchema>;
+type Announce = z.infer<typeof announceNoteSchema>;
+type Update = z.infer<typeof updateActorSchema>;
+type Object = z.infer<typeof objectSchema>;
+type Follow = z.infer<typeof followSchema>;
+type Accept = z.infer<typeof acceptSchema>;
+type Actor = z.infer<typeof actorSchema>;
+type Note = z.infer<typeof noteSchema>;
+type Mention = z.infer<typeof mentionSchema>;
+type Hashtag = z.infer<typeof hashtagSchema>;
+type Emoji = z.infer<typeof emojiSchema>;
+type Like = z.infer<typeof likeSchema>;
+type EmojiReact = z.infer<typeof emojiReactSchema>;
+type Delete = z.infer<typeof deleteSchema>;
+type Zap = z.infer<typeof zapSchema>;
+type Proxy = z.infer<typeof proxySchema>;
+
+export { acceptSchema, activitySchema, actorSchema, emojiSchema, followSchema, imageSchema, noteSchema, objectSchema };
+export type {
+  Accept,
+  Activity,
+  Actor,
+  Announce,
+  CreateNote,
+  Delete,
+  Emoji,
+  EmojiReact,
+  Follow,
+  Hashtag,
+  Like,
+  Mention,
+  Note,
+  Object,
+  Proxy,
+  Update,
+  Zap,
+};
diff --git a/src/transmogrifier/nostr-to-activitypub.ts b/src/transmogrifier/nostr-to-activitypub.ts
new file mode 100644
index 0000000..f7c402a
--- /dev/null
+++ b/src/transmogrifier/nostr-to-activitypub.ts
@@ -0,0 +1,41 @@
+import { Conf } from '@/config.ts';
+import { parseMetaContent } from '@/schema.ts';
+
+import type { Event } from '@/event.ts';
+import type { Actor } from '@/schemas/activitypub.ts';
+
+/** Nostr metadata event to ActivityPub actor. */
+async function toActor(event: Event<0>, username: string): Promise<Actor> {
+  const content = parseMetaContent(event);
+
+  return {
+    type: 'Person',
+    id: Conf.local(`/users/${username}`),
+    name: content?.name || '',
+    preferredUsername: username,
+    inbox: Conf.local(`/users/${username}/inbox`),
+    followers: Conf.local(`/users/${username}/followers`),
+    following: Conf.local(`/users/${username}/following`),
+    outbox: Conf.local(`/users/${username}/outbox`),
+    icon: content.picture
+      ? {
+        type: 'Image',
+        url: content.picture,
+      }
+      : undefined,
+    image: content.banner
+      ? {
+        type: 'Image',
+        url: content.banner,
+      }
+      : undefined,
+    summary: content.about ?? '',
+    attachment: [],
+    tag: [],
+    endpoints: {
+      sharedInbox: Conf.local('/inbox'),
+    },
+  };
+}
+
+export { toActor };
\ No newline at end of file