diff --git a/scripts/verify-build.mjs b/scripts/verify-build.mjs
index df5ce6a..08ba960 100644
--- a/scripts/verify-build.mjs
+++ b/scripts/verify-build.mjs
@@ -12,6 +12,7 @@ const pages = await Promise.all(required.filter((file) => file.endsWith('.html')
 for (const { file, html } of pages) {
   if (html.includes('{{') || html.includes('{%')) throw new Error(`${file} contains an unresolved template placeholder.`);
   if (!/<title>[^<]+<\/title>/.test(html)) throw new Error(`${file} is missing a title.`);
+  if (!html.includes('data-demo-banner') || !html.includes('href="https://sloanops.com/"')) throw new Error(`${file} is missing the SloanOps demo banner.`);
   for (const match of html.matchAll(/(?:src|href)="(\/images\/[^"?#]+)"/g)) await access(resolve(root, `.${match[1]}`));
 }
 
@@ -27,6 +28,10 @@ if (key === 'www') {
 if (key === 'blog') {
   const publishedPosts = ['first-walk-after-work', 'gentler-grooming-day', 'overnight-care-checklist', 'weekend-care-prep'];
   await Promise.all(publishedPosts.map((slug) => access(resolve(root, `posts/${slug}/index.html`))));
+  for (const slug of publishedPosts) {
+    const html = await readFile(resolve(root, `posts/${slug}/index.html`), 'utf8');
+    if (!html.includes('data-demo-banner') || !html.includes('href="https://sloanops.com/"')) throw new Error(`Blog post is missing the SloanOps demo banner: ${slug}.`);
+  }
   if (home.includes('Draft only example for editorial review')) throw new Error('Draft blog post appeared in the journal.');
   try {
     await access(resolve(root, 'posts/draft-only-example/index.html'));
diff --git a/src/components/DemoBanner.astro b/src/components/DemoBanner.astro
new file mode 100644
index 0000000..7bd17ff
--- /dev/null
+++ b/src/components/DemoBanner.astro
@@ -0,0 +1,103 @@
+<aside class="demo-banner" aria-label="Demo website notice" data-demo-banner>
+  <div class="demo-banner__inner">
+    <p>
+      <strong>Demo website</strong>
+      <span>This is a sample site created by SloanOps.</span>
+    </p>
+    <a href="https://sloanops.com/">
+      Return to SloanOps <span aria-hidden="true">↗</span>
+    </a>
+  </div>
+</aside>
+
+<style>
+  .demo-banner {
+    background: #102a3a;
+    color: #f7fbfc;
+    font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
+    position: relative;
+    z-index: 50;
+  }
+
+  .demo-banner__inner {
+    align-items: center;
+    display: flex;
+    gap: 1rem;
+    justify-content: space-between;
+    margin: auto;
+    min-height: 3.5rem;
+    padding: .4rem 0;
+    width: min(75rem, calc(100% - 2rem));
+  }
+
+  p {
+    align-items: center;
+    display: flex;
+    flex-wrap: wrap;
+    font-size: .88rem;
+    gap: .55rem;
+    line-height: 1.35;
+    margin: 0;
+  }
+
+  strong {
+    background: rgba(255, 255, 255, .13);
+    border: 1px solid rgba(255, 255, 255, .24);
+    border-radius: 999px;
+    font-size: .68rem;
+    letter-spacing: .1em;
+    padding: .25rem .5rem;
+    text-transform: uppercase;
+    white-space: nowrap;
+  }
+
+  .demo-banner a {
+    align-items: center;
+    background: #fff;
+    border: 1px solid #fff;
+    border-radius: 999px;
+    color: #102a3a;
+    display: inline-flex;
+    flex: none;
+    font-size: .82rem;
+    font-weight: 800;
+    gap: .4rem;
+    justify-content: center;
+    min-height: 2.75rem;
+    padding: .55rem .85rem;
+    text-decoration: none;
+    transition: background-color .2s ease, color .2s ease, transform .2s ease;
+    white-space: nowrap;
+  }
+
+  .demo-banner a:hover,
+  .demo-banner a:focus-visible {
+    background: #d9f3f0;
+    color: #0b615b;
+    transform: translateY(-.08rem);
+  }
+
+  @media (max-width: 36rem) {
+    .demo-banner__inner {
+      align-items: stretch;
+      flex-direction: column;
+      gap: .55rem;
+      padding: .7rem 0 .75rem;
+    }
+
+    .demo-banner a {
+      align-self: flex-start;
+    }
+  }
+
+  @media (prefers-reduced-motion: reduce) {
+    .demo-banner a {
+      transition: none;
+    }
+
+    .demo-banner a:hover,
+    .demo-banner a:focus-visible {
+      transform: none;
+    }
+  }
+</style>
diff --git a/src/layouts/BaseLayout.astro b/src/layouts/BaseLayout.astro
index ed484c5..b7bb797 100644
--- a/src/layouts/BaseLayout.astro
+++ b/src/layouts/BaseLayout.astro
@@ -1,5 +1,6 @@
 ---
 import '../styles/global.css';
+import DemoBanner from '../components/DemoBanner.astro';
 import Header from '../components/Header.astro';
 import Footer from '../components/Footer.astro';
 import { deployment, isBlog, isProduction, site } from '../lib/site-data.js';
@@ -32,6 +33,7 @@ const structuredData = isBlog ? { '@context': 'https://schema.org', '@type': 'We
     <script type="application/ld+json" set:html={JSON.stringify(structuredData)} />
   </head>
   <body style={`--accent:${site.theme.accent};--ink:${site.theme.ink};--surface:${site.theme.surface}`}>
+    <DemoBanner />
     <Header />
     <main><slot /></main>
     <Footer />