diff --git a/src/server/middleware.ts b/src/server/middleware.ts
index 5a5805a..c414539 100644
--- a/src/server/middleware.ts
+++ b/src/server/middleware.ts
@@ -107,6 +107,9 @@ export function securityHeaders(
     `frame-ancestors 'none'`,
     `object-src 'none'`,
     `script-src 'self' https://crawlproof.com`,
+    // The one ad unit is a cross-origin CrawlProof frame (/api/ads/frame), so
+    // it costs this entry and nothing else: no script, no style, no storage.
+    `frame-src https://crawlproof.com`,
     `style-src 'self' 'unsafe-inline'`,
     // Employer logos and avatars come from wherever the employer hosts them.
     // 'self' has to be listed explicitly: omitting it works in production and
diff --git a/src/views/ad-unit.tsx b/src/views/ad-unit.tsx
new file mode 100644
index 0000000..a61b4d7
--- /dev/null
+++ b/src/views/ad-unit.tsx
@@ -0,0 +1,66 @@
+/**
+ * One CrawlProof ad unit, as a script-free cross-origin iframe.
+ *
+ * `ad.js` fills a placeholder with a `srcdoc` iframe, and a srcdoc document
+ * inherits this page's Content-Security-Policy: the creative's inline styles
+ * and remote images would only render with a far looser policy than this
+ * board sends. `/api/ads/frame` serves the same creative as a real
+ * cross-origin document, so the cost here is one `frame-src` entry, no
+ * third-party JavaScript and nothing written to this origin's storage.
+ * Impressions are metered server-side exactly as on the script path.
+ *
+ * The format is `text_link`, the one fluid creative: 40px tall at any width,
+ * with its own "Sponsored" mark. Banners are laid out at a fixed pixel width
+ * and would be cropped in a narrow column, and choosing by viewport needs a
+ * script. No `&theme=`: the frame answers prefers-color-scheme itself.
+ */
+import type { FC } from 'hono/jsx';
+
+export const AD_ORIGIN = 'https://crawlproof.com';
+export const AD_SLOT = '9c3d6e3d-ae1f-43ff-b6d9-4f42f11725ce';
+
+/** First path segments that never carry an ad: flows, accounts, dashboards, admin. */
+const NO_AD_SEGMENTS = new Set([
+  'tracker',
+  'fleets',
+  'post',
+  'post-a-job',
+  'me',
+  'inbox',
+  'notifications',
+  'applications',
+  'admin',
+  'login',
+  'auth',
+  'device',
+  'invoices',
+  'coinpay',
+  'revisions',
+]);
+
+/** Public, indexable pages only. A noindex page is a dashboard or a one-off flow. */
+export function showsAd(path: string, noindex?: boolean): boolean {
+  if (noindex) return false;
+  const first = path.split(/[/?#]/)[1] ?? '';
+  return !NO_AD_SEGMENTS.has(first);
+}
+
+export const AdUnit: FC<{ format?: 'text_link' }> = ({ format = 'text_link' }) => {
+  const src = `${AD_ORIGIN}/api/ads/frame?slot=${encodeURIComponent(AD_SLOT)}&format=${encodeURIComponent(format)}`;
+  return (
+    <aside class="ad-unit" data-ad-format={format} aria-label="Advertisement">
+      <div class="container">
+        {/* No allow-scripts, no allow-same-origin: the creative is static HTML.
+            The popup permissions let its click-through open a new tab. */}
+        <iframe
+          src={src}
+          title="Advertisement"
+          height="40"
+          loading="lazy"
+          scrolling="no"
+          sandbox="allow-popups allow-popups-to-escape-sandbox allow-top-navigation-by-user-activation"
+        ></iframe>
+      </div>
+    </aside>
+  );
+};
diff --git a/src/views/layout.tsx b/src/views/layout.tsx
index 11f3f1c..305c33f 100644
--- a/src/views/layout.tsx
+++ b/src/views/layout.tsx
@@ -16,6 +16,7 @@ import type { SkillCount } from '../core/skills.ts';
 import { pathForQuery } from '../core/landing.ts';
 import { EMPTY_QUERY } from '../schema/query.ts';
 import { pfsFooter } from './pfs-footer.ts';
+import { AdUnit, showsAd } from './ad-unit.tsx';
 
 export interface PageProps {
   title: string;
@@ -268,6 +269,7 @@ export const Layout: FC<PropsWithChildren<PageProps>> = (props) => {
         <main id="main">
           <div class="container">{children}</div>
         </main>
+        {showsAd(path, noindex) && <AdUnit />}
         {skills.length > 0 && (
           <footer class="site-footer">
             <div class="container footer-skills">
diff --git a/test/views.test.ts b/test/views.test.ts
index 1f0f051..508ecef 100644
--- a/test/views.test.ts
+++ b/test/views.test.ts
@@ -556,3 +556,36 @@ test('a signed-out visitor is offered somewhere to hire from', async () => {
   // Signed in, the nav already has a button to the form; two would be noise.
   assert.match(nav({ id: 'u' }), /href="\/post"/, 'signed in, the form is still one click away');
 });
+
+test('the ad unit is a crawlproof frame on public pages only, and the policy frames it', async () => {
+  const { showsAd, AD_SLOT } = await import('../dist/views/ad-unit.js');
+  const { Layout } = await import('../dist/views/layout.js');
+  const { securityHeaders } = await import('../dist/server/middleware.js');
+  assert.equal(showsAd('/', false), true);
+  assert.equal(showsAd('/jobs/abc', false), true);
+  assert.equal(showsAd('/me/settings', false), false);
+  assert.equal(showsAd('/post-a-job', false), false);
+  assert.equal(showsAd('/tracker', false), false);
+  assert.equal(showsAd('/jobs/abc', true), false);
+
+  const page = (path: string) =>
+    String(
+      Layout({
+        title: 'A board',
+        viewer: null,
+        boardName: 'A board',
+        publicUrl: 'https://example.test',
+        path,
+        children: 'x',
+      }),
+    );
+  const home = page('/');
+  assert.equal(home.match(/crawlproof\.com\/api\/ads\/frame/g)?.length, 1, 'exactly one unit');
+  assert.ok(home.includes(`slot=${AD_SLOT}&amp;format=text_link`), home);
+  assert.ok(!home.includes('theme='), 'the frame answers prefers-color-scheme itself');
+  assert.ok(!page('/inbox').includes('/api/ads/frame'), 'no ad inside the inbox');
+
+  const headers = new Headers();
+  await securityHeaders()({ res: { headers } } as never, async () => undefined);
+  assert.match(headers.get('content-security-policy') ?? '', /frame-src https:\/\/crawlproof\.com/);
+});
diff --git a/web/public/app.css b/web/public/app.css
index 4341383..c1b7b4f 100644
--- a/web/public/app.css
+++ b/web/public/app.css
@@ -1099,3 +1099,15 @@ a.badge-plain:hover .badge {
 .tracker-metrics .card-content { padding: 1rem; }
 .tracker-missing { color: var(--warning); font-size: 0.9rem; margin: 0.25rem 0; }
 .tracker-improve ul { margin: 0; padding-left: 1.25rem; display: grid; gap: 0.5rem; }
+
+/* CrawlProof ad unit (src/views/ad-unit.tsx): one fluid text_link frame above the footer. */
+.ad-unit {
+  margin: 1.5rem 0 0;
+}
+.ad-unit iframe {
+  display: block;
+  width: 100%;
+  height: 40px;
+  border: 0;
+  background: transparent;
+}
diff --git a/web/public/sw.js b/web/public/sw.js
index 08039da..40d32d8 100644
--- a/web/public/sw.js
+++ b/web/public/sw.js
@@ -13,7 +13,7 @@
  * drifted, which is the only version of this rule that survives contact.
  */
 
-const VERSION = 'ea250e72';
+const VERSION = '4a4fd178';
 const SHELL = `shell-${VERSION}`;
 const ASSETS = ['/assets/app.css', '/assets/tokens.css', '/assets/icon.svg'];