diff --git a/public/demo.html b/public/demo.html
index 441822c..a4b197e 100644
--- a/public/demo.html
+++ b/public/demo.html
@@ -91,7 +91,7 @@
 
   <header>
     <h1>Equalify Iris</h1>
-    <p class="tagline">Turn images of document pages into accessible HTML.</p>
+    <p class="tagline">Turn a PDF or page images into accessible HTML<span id="tagline-pdf" hidden>, and get the PDF back tagged</span>.</p>
     <!-- Filled from GET /v1/stats after load, and left hidden if that fails or
          nothing has been converted yet: an empty boast is worse than none. Not a
          live region — it is page content that happens to arrive late, not a
@@ -754,6 +754,7 @@ <h2 class="visually-hidden">About</h2>
         if (!res.ok) return;
         const l = await res.json();
         taggedPdfOn = Boolean(l && l.tagged_pdf === true);
+        $('tagline-pdf').hidden = !taggedPdfOn;
         const bytes = Number(l && l.image && l.image.max_bytes);
         if (!Number.isFinite(bytes) || bytes < 1) return;
         uploadLimits = { maxBytes: bytes, hint: String(l.image.hint || '') };
diff --git a/test/demo-tagline.test.ts b/test/demo-tagline.test.ts
new file mode 100644
index 0000000..0687a60
--- /dev/null
+++ b/test/demo-tagline.test.ts
@@ -0,0 +1,45 @@
+// The tagline's tagged-PDF clause shows only where GET /v1/limits reports `tagged_pdf`.
+//
+// `loadLimits` is lifted out of the inline script, as in test/demo-tally.test.ts, and run
+// against a stub `fetch` and a `$` that only finds ids present in the page. A renamed span
+// would make `$` return null, and the throw would be swallowed with the limits hint.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+const demoHtml = readFileSync(join(import.meta.dirname, "..", "public", "demo.html"), "utf8");
+
+function extract(name: string): string {
+  const start = demoHtml.indexOf(`async function ${name}(`);
+  assert.notEqual(start, -1, `${name} is no longer in public/demo.html`);
+  let depth = 0;
+  for (let i = demoHtml.indexOf("{", start); i < demoHtml.length; i++) {
+    if (demoHtml[i] === "{") depth++;
+    else if (demoHtml[i] === "}" && --depth === 0) return demoHtml.slice(start, i + 1);
+  }
+  throw new Error(`unbalanced braces reading ${name} from public/demo.html`);
+}
+
+async function run(limits: unknown) {
+  const els = new Map<string, { hidden: boolean; textContent: string; setAttribute: () => void }>();
+  for (const m of demoHtml.matchAll(/<[a-z0-9]+\b[^>]*\bid="([^"]+)"[^>]*>/g)) {
+    els.set(m[1]!, { hidden: /\shidden[\s>]/.test(m[0]), textContent: "", setAttribute: () => {} });
+  }
+  const $ = (id: string) => els.get(id) ?? null;
+  const fetch = async () => ({ ok: true, json: async () => limits });
+  const body = `let taggedPdfOn = false, uploadLimits = null; ${extract("loadLimits")}; return loadLimits();`;
+  await new Function("$", "fetch", "API", body)($, fetch, "/v1");
+  return { clause: els.get("tagline-pdf"), hint: els.get("limits-hint")!.textContent };
+}
+
+test("the tagline names a tagged PDF only where the deployment makes one", async () => {
+  assert.match(demoHtml, /<p class="tagline">[^<]*<span id="tagline-pdf" hidden>, and get the PDF back tagged<\/span>\.<\/p>/);
+  const image = { max_bytes: 5, hint: "Up to 5 B.", media_types: ["image/png"] };
+  const on = await run({ tagged_pdf: true, image });
+  assert.equal(on.clause?.hidden, false);
+  assert.equal(on.hint, "Up to 5 B.", "the toggle does not break the rest of loadLimits");
+  assert.equal((await run({ tagged_pdf: false, image })).clause?.hidden, true);
+  assert.equal((await run({ image })).clause?.hidden, true);
+  assert.equal((await run({ tagged_pdf: true })).clause?.hidden, false, "even with no image limits");
+});