diff --git a/src/controllers/api/accounts.ts b/src/controllers/api/accounts.ts
index 27cf7590..1ae6a4f6 100644
--- a/src/controllers/api/accounts.ts
+++ b/src/controllers/api/accounts.ts
@@ -15,6 +15,7 @@ import { renderAccounts, renderEventAccounts, renderStatuses } from '@/views.ts'
 import { accountFromPubkey, renderAccount } from '@/views/mastodon/accounts.ts';
 import { renderRelationship } from '@/views/mastodon/relationships.ts';
 import { renderReblog, renderStatus } from '@/views/mastodon/statuses.ts';
+import { metadataSchema } from '@/schemas/nostr.ts';
 import { hydrateEvents } from '@/storages/hydrate.ts';
 import { bech32ToPubkey } from '@/utils.ts';
 import { addTag, deleteTag, findReplyTag, getTagSet } from '@/utils/tags.ts';
@@ -269,6 +270,7 @@ const updateCredentialsSchema = z.object({
   pleroma_settings_store: z.record(z.string(), z.unknown()).optional(),
   lud16: z.string().email().or(z.literal('')).optional(),
   website: z.string().url().or(z.literal('')).optional(),
+  fields_attributes: z.object({ name: z.string(), value: z.string() }).array().optional(),
 });
 
 const updateCredentialsController: AppController = async (c) => {
@@ -284,11 +286,12 @@ const updateCredentialsController: AppController = async (c) => {
   const event = await updateEvent(
     { kinds: [0], authors: [pubkey], limit: 1 },
     async (prev) => {
-      const meta = n.json().pipe(n.metadata()).catch({}).parse(prev.content);
+      const meta = n.json().pipe(metadataSchema).catch({}).parse(prev.content);
       const {
         avatar: avatarFile,
         header: headerFile,
         display_name,
+        fields_attributes,
         note,
         nip05,
         lud16,
@@ -316,6 +319,10 @@ const updateCredentialsController: AppController = async (c) => {
       if (lud16 === '') delete meta.lud16;
       if (website === '') delete meta.website;
 
+      if (fields_attributes) {
+        meta.fields = fields_attributes.map(({ name, value }) => [name, value]);
+      }
+
       return {
         kind: 0,
         content: JSON.stringify(meta),
diff --git a/src/schemas/nostr.ts b/src/schemas/nostr.ts
index 4e8f917d..05cd0f31 100644
--- a/src/schemas/nostr.ts
+++ b/src/schemas/nostr.ts
@@ -9,6 +9,11 @@ const signedEventSchema = n.event()
   .refine((event) => event.id === getEventHash(event), 'Event ID does not match hash')
   .refine(verifyEvent, 'Event signature is invalid');
 
+/** Kind 0 standardized fields extended with Ditto custom fields. */
+const metadataSchema = n.metadata().and(z.object({
+  fields: z.tuple([z.string(), z.string()]).array().optional().catch(undefined),
+}));
+
 /**
  * Stored in the kind 0 content.
  * https://developer.mozilla.org/en-US/docs/Web/Manifest/screenshots
@@ -63,4 +68,12 @@ const emojiTagSchema = z.tuple([z.literal('emoji'), z.string(), z.string().url()
 /** NIP-30 custom emoji tag. */
 type EmojiTag = z.infer<typeof emojiTagSchema>;
 
-export { type EmojiTag, emojiTagSchema, relayInfoDocSchema, screenshotsSchema, serverMetaSchema, signedEventSchema };
+export {
+  type EmojiTag,
+  emojiTagSchema,
+  metadataSchema,
+  relayInfoDocSchema,
+  screenshotsSchema,
+  serverMetaSchema,
+  signedEventSchema,
+};
diff --git a/src/utils/api.ts b/src/utils/api.ts
index e7766979..829a2cce 100644
--- a/src/utils/api.ts
+++ b/src/utils/api.ts
@@ -2,7 +2,6 @@ import { type Context } from '@hono/hono';
 import { HTTPException } from '@hono/hono/http-exception';
 import { NostrEvent, NostrFilter } from '@nostrify/nostrify';
 import Debug from '@soapbox/stickynotes/debug';
-import { parseFormData } from 'formdata-helper';
 import { EventTemplate } from 'nostr-tools';
 import * as TypeFest from 'type-fest';
 
@@ -13,6 +12,7 @@ import { RelayError } from '@/RelayError.ts';
 import { AdminSigner } from '@/signers/AdminSigner.ts';
 import { Storages } from '@/storages.ts';
 import { nostrNow } from '@/utils.ts';
+import { parseFormData } from '@/utils/formdata.ts';
 import { purifyEvent } from '@/utils/purify.ts';
 
 const debug = Debug('ditto:api');
@@ -182,7 +182,11 @@ async function parseBody(req: Request): Promise<unknown> {
   switch (req.headers.get('content-type')?.split(';')[0]) {
     case 'multipart/form-data':
     case 'application/x-www-form-urlencoded':
-      return parseFormData(await req.formData());
+      try {
+        return parseFormData(await req.formData());
+      } catch {
+        throw new HTTPException(400, { message: 'Invalid form data' });
+      }
     case 'application/json':
       return req.json();
   }
diff --git a/src/utils/formdata.test.ts b/src/utils/formdata.test.ts
new file mode 100644
index 00000000..3eaf02aa
--- /dev/null
+++ b/src/utils/formdata.test.ts
@@ -0,0 +1,30 @@
+import { assertEquals, assertThrows } from '@std/assert';
+
+import { parseFormData } from '@/utils/formdata.ts';
+
+Deno.test('parseFormData', () => {
+  const formData = new FormData();
+
+  formData.append('foo', 'bar');
+  formData.append('fields_attributes[0][name]', 'baz');
+  formData.append('fields_attributes[0][value]', 'qux');
+  formData.append('fields_attributes[1][name]', 'quux');
+  formData.append('fields_attributes[1][value]', 'corge');
+
+  const result = parseFormData(formData);
+
+  assertEquals(result, {
+    foo: 'bar',
+    fields_attributes: [
+      { name: 'baz', value: 'qux' },
+      { name: 'quux', value: 'corge' },
+    ],
+  });
+
+  assertThrows(() => {
+    const formData = new FormData();
+    formData.append('fields_attributes[1]', 'unexpected');
+    formData.append('fields_attributes[1][extra]', 'extra_value');
+    parseFormData(formData);
+  });
+});
diff --git a/src/utils/formdata.ts b/src/utils/formdata.ts
new file mode 100644
index 00000000..6d5d997b
--- /dev/null
+++ b/src/utils/formdata.ts
@@ -0,0 +1,43 @@
+import { parseFormData as _parseFormData } from 'formdata-helper';
+
+/** Parse formData into JSON, simulating the way Mastodon does it. */
+export function parseFormData(formData: FormData): unknown {
+  const json = _parseFormData(formData);
+
+  const parsed: Record<string, unknown> = {};
+
+  for (const [key, value] of Object.entries(json)) {
+    deepSet(parsed, key, value);
+  }
+
+  return parsed;
+}
+
+/** Deeply sets a value in an object based on a Rails-style nested key. */
+function deepSet(
+  /** The target object to modify. */
+  target: Record<string, any>,
+  /** The Rails-style key (e.g., "fields_attributes[0][name]"). */
+  key: string,
+  /** The value to set. */
+  value: any,
+): void {
+  const keys = key.match(/[^[\]]+/g); // Extract keys like ["fields_attributes", "0", "name"]
+  if (!keys) return;
+
+  let current = target;
+
+  keys.forEach((k, index) => {
+    const isLast = index === keys.length - 1;
+
+    if (isLast) {
+      current[k] = value; // Set the value at the final key
+    } else {
+      if (!current[k]) {
+        // Determine if the next key is numeric, then create an array; otherwise, an object
+        current[k] = /^\d+$/.test(keys[index + 1]) ? [] : {};
+      }
+      current = current[k];
+    }
+  });
+}
diff --git a/src/views/mastodon/accounts.ts b/src/views/mastodon/accounts.ts
index 6d0e0446..927b00d5 100644
--- a/src/views/mastodon/accounts.ts
+++ b/src/views/mastodon/accounts.ts
@@ -4,6 +4,7 @@ import { nip19, UnsignedEvent } from 'nostr-tools';
 import { Conf } from '@/config.ts';
 import { MastodonAccount } from '@/entities/MastodonAccount.ts';
 import { type DittoEvent } from '@/interfaces/DittoEvent.ts';
+import { metadataSchema } from '@/schemas/nostr.ts';
 import { getLnurl } from '@/utils/lnurl.ts';
 import { parseAndVerifyNip05 } from '@/utils/nip05.ts';
 import { parseNoteContent } from '@/utils/note.ts';
@@ -42,7 +43,8 @@ async function renderAccount(
     lud06,
     lud16,
     website,
-  } = n.json().pipe(n.metadata()).catch({}).parse(event.content);
+    fields: _fields,
+  } = n.json().pipe(metadataSchema).catch({}).parse(event.content);
 
   const npub = nip19.npubEncode(pubkey);
   const nprofile = nip19.nprofileEncode({ pubkey, relays: [Conf.relay] });
@@ -58,6 +60,7 @@ async function renderAccount(
     }
   }
   const { html } = parseNoteContent(about || '', []);
+  const fields = _fields?.map(([name, value]) => ({ name, value, verified_at: null })) ?? [];
 
   return {
     id: pubkey,
@@ -69,7 +72,7 @@ async function renderAccount(
     discoverable: true,
     display_name: name ?? '',
     emojis: renderEmojis(event),
-    fields: [],
+    fields,
     follow_requests_count: 0,
     followers_count: event.author_stats?.followers_count ?? 0,
     following_count: event.author_stats?.following_count ?? 0,
@@ -82,7 +85,7 @@ async function renderAccount(
     roles: [],
     source: opts.withSource
       ? {
-        fields: [],
+        fields,
         language: '',
         note: about || '',
         privacy: 'public',