diff --git a/extension/src/shared/form-affordances/__tests__/group-autocomplete.test.ts b/extension/src/shared/form-affordances/__tests__/group-autocomplete.test.ts
new file mode 100644
index 0000000..da6b0ed
--- /dev/null
+++ b/extension/src/shared/form-affordances/__tests__/group-autocomplete.test.ts
@@ -0,0 +1,35 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { wireGroupAutocomplete } from '../group-autocomplete';
+
+describe('wireGroupAutocomplete', () => {
+  let form: HTMLElement;
+
+  beforeEach(() => {
+    // Clean up any datalist from a prior test
+    document.getElementById('groups-datalist')?.remove();
+    form = document.createElement('div');
+    form.innerHTML = `<input id="f-group" type="text" />`;
+    document.body.appendChild(form);
+  });
+
+  it('attaches datalist with all groups', async () => {
+    const sendMessage = vi.fn().mockResolvedValue({
+      ok: true,
+      data: { groups: ['personal', 'work', 'finance'] },
+    });
+    await wireGroupAutocomplete(form, { sendMessage });
+    const list = document.getElementById('groups-datalist') as HTMLDataListElement | null;
+    expect(list).not.toBeNull();
+    const opts = Array.from(list!.querySelectorAll('option')).map((o) => o.value);
+    expect(opts).toEqual(['personal', 'work', 'finance']);
+    const input = form.querySelector('#f-group') as HTMLInputElement;
+    expect(input.getAttribute('list')).toBe('groups-datalist');
+  });
+
+  it('is a no-op if SW returns error', async () => {
+    const sendMessage = vi.fn().mockResolvedValue({ ok: false, error: 'vault_locked' });
+    await wireGroupAutocomplete(form, { sendMessage });
+    const input = form.querySelector('#f-group') as HTMLInputElement;
+    expect(input.getAttribute('list')).toBeNull();
+  });
+});
diff --git a/extension/src/shared/form-affordances/group-autocomplete.ts b/extension/src/shared/form-affordances/group-autocomplete.ts
new file mode 100644
index 0000000..60a4c89
--- /dev/null
+++ b/extension/src/shared/form-affordances/group-autocomplete.ts
@@ -0,0 +1,23 @@
+export interface GroupAutocompleteOpts {
+  sendMessage: (msg: { type: 'list_groups' }) => Promise<{ ok: boolean; data?: { groups: string[] }; error?: string }>;
+}
+
+const DATALIST_ID = 'groups-datalist';
+
+export async function wireGroupAutocomplete(form: HTMLElement, opts: GroupAutocompleteOpts): Promise<void> {
+  const input = form.querySelector<HTMLInputElement>('#f-group');
+  if (!input) return;
+  const resp = await opts.sendMessage({ type: 'list_groups' });
+  if (!resp.ok || !resp.data) return;
+
+  // Datalists must live in the document, not nested inside an input. Reuse if
+  // we've already mounted one this session.
+  let list = document.getElementById(DATALIST_ID) as HTMLDataListElement | null;
+  if (!list) {
+    list = document.createElement('datalist');
+    list.id = DATALIST_ID;
+    document.body.appendChild(list);
+  }
+  list.innerHTML = resp.data.groups.map((g) => `<option value="${g.replace(/"/g, '&quot;')}"></option>`).join('');
+  input.setAttribute('list', DATALIST_ID);
+}