diff --git a/supabase/seed.sql b/supabase/seed.sql
new file mode 100644
index 0000000..201b11a
--- /dev/null
+++ b/supabase/seed.sql
@@ -0,0 +1,71 @@
+-- Seed data for Supabase branch databases (preview deploys)
+-- This file runs automatically when a branch DB is created via Supabase Branching.
+
+-- ============================================================================
+-- Test auth user: test@example.com / testpassword123
+-- ============================================================================
+
+INSERT INTO auth.users (
+  id,
+  instance_id,
+  aud,
+  role,
+  email,
+  encrypted_password,
+  email_confirmed_at,
+  raw_app_meta_data,
+  raw_user_meta_data,
+  created_at,
+  updated_at,
+  confirmation_token,
+  recovery_token
+) VALUES (
+  'a1b2c3d4-e5f6-7890-abcd-ef1234567890',
+  '00000000-0000-0000-0000-000000000000',
+  'authenticated',
+  'authenticated',
+  'test@example.com',
+  crypt('testpassword123', gen_salt('bf')),
+  now(),
+  '{"provider": "email", "providers": ["email"]}',
+  '{}',
+  now(),
+  now(),
+  '',
+  ''
+);
+
+INSERT INTO auth.identities (
+  id,
+  user_id,
+  identity_data,
+  provider,
+  provider_id,
+  last_sign_in_at,
+  created_at,
+  updated_at
+) VALUES (
+  'a1b2c3d4-e5f6-7890-abcd-ef1234567890',
+  'a1b2c3d4-e5f6-7890-abcd-ef1234567890',
+  jsonb_build_object('sub', 'a1b2c3d4-e5f6-7890-abcd-ef1234567890', 'email', 'test@example.com'),
+  'email',
+  'a1b2c3d4-e5f6-7890-abcd-ef1234567890',
+  now(),
+  now(),
+  now()
+);
+
+-- ============================================================================
+-- Sample sites
+-- ============================================================================
+
+INSERT INTO sites (id, name, url) VALUES
+  ('11111111-1111-1111-1111-111111111111', 'Example Site', 'https://example.com'),
+  ('22222222-2222-2222-2222-222222222222', 'Anthropic', 'https://www.anthropic.com');
+
+-- ============================================================================
+-- Test contact
+-- ============================================================================
+
+INSERT INTO contacts (email) VALUES
+  ('test@example.com');