diff --git a/functions/_lib/drink-preview.js b/functions/_lib/drink-preview.js
index cea56633..0266624c 100644
--- a/functions/_lib/drink-preview.js
+++ b/functions/_lib/drink-preview.js
@@ -62,5 +62,8 @@ export async function fetchDrinkData(festivalId, category) {
   const url = `${DATA_BASE_URL}/${encodeURIComponent(festivalId)}/${encodeURIComponent(category)}.json`;
   const response = await fetch(url);
   if (!response.ok) return null;
-  return response.json();
+  const data = await response.json();
+  if (Array.isArray(data)) return data;
+  if (data && Array.isArray(data.producers)) return data.producers;
+  return null;
 }
diff --git a/functions/test/drink-preview.test.js b/functions/test/drink-preview.test.js
index 75d18e52..8a9004c3 100644
--- a/functions/test/drink-preview.test.js
+++ b/functions/test/drink-preview.test.js
@@ -1,5 +1,5 @@
-import { describe, it, expect } from 'vitest';
-import { isCrawler, findDrink, buildOgTags } from '../_lib/drink-preview.js';
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { isCrawler, findDrink, buildOgTags, fetchDrinkData } from '../_lib/drink-preview.js';
 
 const TEST_PRODUCERS = [
   {
@@ -194,3 +194,74 @@ describe('buildOgTags', () => {
   });
 });
 
+describe('fetchDrinkData', () => {
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it('returns producers array from wrapped API response', async () => {
+    const producers = [{ id: 'adnams', name: 'Adnams', products: [] }];
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ producers, timestamp: '2025-01-01' }),
+    }));
+    const result = await fetchDrinkData('cbf2025', 'beer');
+    expect(result).toEqual(producers);
+  });
+
+  it('returns array directly when API response is already an array', async () => {
+    const producers = [{ id: 'adnams', name: 'Adnams', products: [] }];
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve(producers),
+    }));
+    const result = await fetchDrinkData('cbf2025', 'beer');
+    expect(result).toEqual(producers);
+  });
+
+  it('returns null when response is not ok', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({ ok: false, status: 404 }));
+    const result = await fetchDrinkData('cbf2025', 'beer');
+    expect(result).toBeNull();
+  });
+
+  it('returns null when wrapped response has no producers key', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ timestamp: '2025-01-01' }),
+    }));
+    const result = await fetchDrinkData('cbf2025', 'beer');
+    expect(result).toBeNull();
+  });
+
+  it('returns null when response.json() resolves to null', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve(null),
+    }));
+    const result = await fetchDrinkData('cbf2025', 'beer');
+    expect(result).toBeNull();
+  });
+
+  it('returns null when producers field exists but is not an array', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ producers: 'not-an-array' }),
+    }));
+    const result = await fetchDrinkData('cbf2025', 'beer');
+    expect(result).toBeNull();
+  });
+
+  it('fetches the correct URL for a given festival and category', async () => {
+    const mockFetch = vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ producers: [] }),
+    });
+    vi.stubGlobal('fetch', mockFetch);
+    await fetchDrinkData('cbf2025', 'beer');
+    expect(mockFetch).toHaveBeenCalledWith(
+      'https://data.cambeerfestival.app/cbf2025/beer.json',
+    );
+  });
+});
+
diff --git a/functions/test/handler.test.js b/functions/test/handler.test.js
new file mode 100644
index 00000000..3f72247b
--- /dev/null
+++ b/functions/test/handler.test.js
@@ -0,0 +1,155 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { onRequest } from '../[festivalId]/drink/[category]/[drinkId].js';
+
+// Minimal HTMLRewriter mock: collects appended HTML and inserts it before </head>.
+class MockHTMLRewriter {
+  constructor() {
+    this._headHandler = null;
+  }
+  on(selector, handler) {
+    if (selector === 'head') this._headHandler = handler;
+    return this;
+  }
+  async transform(response) {
+    const text = await response.text();
+    let injected = '';
+    if (this._headHandler) {
+      // Second arg ({ html: true }) is intentionally ignored in this mock.
+      const element = { append: (html) => { injected += html; } };
+      this._headHandler.element(element);
+    }
+    return new Response(text.replace('</head>', injected + '</head>'), {
+      status: response.status,
+      headers: response.headers,
+    });
+  }
+}
+
+const SPA_HTML = '<!DOCTYPE html><html><head><title>CBF</title></head><body></body></html>';
+
+const TEST_PRODUCERS = [
+  {
+    id: 'adnams',
+    name: 'Adnams',
+    location: 'Southwold',
+    products: [
+      { id: 'broadside', name: 'Broadside', style: 'Strong Bitter', abv: 6.3, category: 'beer' },
+    ],
+  },
+];
+
+function makeSpaResponse() {
+  return new Response(SPA_HTML, { headers: { 'Content-Type': 'text/html' } });
+}
+
+function makeContext({ ua, festivalId = 'cbf2025', category = 'beer', drinkId = 'broadside' } = {}) {
+  const url = `https://cambeerfestival.app/${festivalId}/drink/${category}/${drinkId}`;
+  return {
+    request: new Request(url, {
+      headers: { 'User-Agent': ua ?? 'Mozilla/5.0 Chrome/120' },
+    }),
+    env: {
+      ASSETS: { fetch: vi.fn().mockResolvedValue(makeSpaResponse()) },
+    },
+    params: { festivalId, category, drinkId },
+  };
+}
+
+beforeEach(() => {
+  vi.stubGlobal('HTMLRewriter', MockHTMLRewriter);
+  vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+    ok: true,
+    json: () => Promise.resolve({ producers: TEST_PRODUCERS }),
+  }));
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
+
+describe('onRequest — non-crawler passthrough', () => {
+  it('calls ASSETS.fetch and returns immediately for a regular browser', async () => {
+    const ctx = makeContext({ ua: 'Mozilla/5.0 Chrome/120' });
+    await onRequest(ctx);
+    expect(ctx.env.ASSETS.fetch).toHaveBeenCalledWith(ctx.request);
+    expect(global.fetch).not.toHaveBeenCalled();
+  });
+
+  it('does not inject OG tags for a regular browser', async () => {
+    const ctx = makeContext({ ua: 'Mozilla/5.0 Chrome/120' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).not.toContain('og:title');
+  });
+});
+
+describe('onRequest — crawler OG injection', () => {
+  it('injects og:title with drink name and brewery for Googlebot', async () => {
+    const ctx = makeContext({ ua: 'Googlebot/2.1' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).toContain('og:title');
+    expect(text).toContain('Broadside — Adnams');
+  });
+
+  it('injects og:url with the canonical drink URL', async () => {
+    const ctx = makeContext({ ua: 'Googlebot/2.1', festivalId: 'cbf2025', category: 'beer', drinkId: 'broadside' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).toContain('https://cambeerfestival.app/cbf2025/drink/beer/broadside');
+  });
+
+  it('injects OG tags for WhatsApp crawler', async () => {
+    const ctx = makeContext({ ua: 'WhatsApp/2.19.81 A' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).toContain('og:title');
+  });
+
+  it('fetches drink data from the correct festival and category', async () => {
+    const ctx = makeContext({ ua: 'Googlebot/2.1', festivalId: 'cbf2024', category: 'cider', drinkId: 'broadside' });
+    const mockFetch = vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ producers: TEST_PRODUCERS }),
+    });
+    vi.stubGlobal('fetch', mockFetch);
+    await onRequest(ctx);
+    expect(mockFetch).toHaveBeenCalledWith(
+      expect.stringContaining('cbf2024/cider.json'),
+    );
+  });
+
+  it('preserves the rest of the SPA HTML when injecting', async () => {
+    const ctx = makeContext({ ua: 'Googlebot/2.1' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).toContain('<title>CBF</title>');
+    expect(text).toContain('<body></body>');
+  });
+});
+
+describe('onRequest — crawler fallback paths', () => {
+  it('returns unmodified SPA when API responds with non-ok status', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockResolvedValue({ ok: false, status: 404 }));
+    const ctx = makeContext({ ua: 'Googlebot/2.1' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).not.toContain('og:title');
+    expect(text).toBe(SPA_HTML);
+  });
+
+  it('returns unmodified SPA when fetch throws a network error', async () => {
+    vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('Network failure')));
+    const ctx = makeContext({ ua: 'Googlebot/2.1' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).not.toContain('og:title');
+  });
+
+  it('returns unmodified SPA when the drink ID is not found', async () => {
+    const ctx = makeContext({ ua: 'Googlebot/2.1', drinkId: 'nonexistent' });
+    const response = await onRequest(ctx);
+    const text = await response.text();
+    expect(text).not.toContain('og:title');
+  });
+});