diff --git a/.github/workflows/_checks.yml b/.github/workflows/_checks.yml
index 0a4305a..d1b5853 100644
--- a/.github/workflows/_checks.yml
+++ b/.github/workflows/_checks.yml
@@ -23,7 +23,8 @@ jobs:
       - uses: actions/checkout@v6
       - uses: extractions/setup-just@v4
       - uses: astral-sh/setup-uv@v8.2.0
-      - run: just docs-build
+      - run: just docs-demos-browser
+      - run: just docs-demos
 
   pytest:
     runs-on: ubuntu-latest
diff --git a/justfile b/justfile
index e84727d..78a6047 100644
--- a/justfile
+++ b/justfile
@@ -47,3 +47,13 @@ publish:
 # Build the docs site, failing on broken links / nav warnings; CI runs this on every PR.
 docs-build:
     uvx --with-requirements docs/requirements.txt mkdocs build --strict
+
+playwright := "playwright==1.64.0"
+
+# Install the Chromium that docs-demos drives; --with-deps adds its system libraries on Linux.
+docs-demos-browser:
+    uvx --from {{ playwright }} playwright install --with-deps chromium
+
+# Play every demo tour at phone and desktop width and fail on layout breakage or page errors.
+docs-demos: docs-build
+    uvx --with {{ playwright }} python -I scripts/check_demos.py site
diff --git a/pyproject.toml b/pyproject.toml
index d2abb07..f253bbf 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -113,6 +113,10 @@ isort.no-lines-before = ["standard-library", "local-folder"]
 "src/httpware/client.py" = ["ASYNC109", "ANN401"]
 "tests/**" = ["S101"]
 
+[[tool.ty.overrides]]
+include = ["scripts/**"]
+rules = { unresolved-import = "ignore" }
+
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 addopts = ""
@@ -125,6 +129,6 @@ markers = [
 
 [tool.coverage]
 run.concurrency = ["thread"]
-run.omit = ["benchmarks/*"]
+run.omit = ["benchmarks/*", "scripts/*"]
 report.exclude_also = ["if typing.TYPE_CHECKING:"]
 report.fail_under = 100
diff --git a/scripts/__init__.py b/scripts/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/scripts/check_demos.py b/scripts/check_demos.py
new file mode 100644
index 0000000..0ec9290
--- /dev/null
+++ b/scripts/check_demos.py
@@ -0,0 +1,147 @@
+"""Play every guided tour in the built docs demos and check their layout in a real browser.
+
+Usage: `just docs-demos`, which builds the site and runs this against it.
+
+At a phone and a desktop viewport, every demo page is checked on load, at every tour stop and
+after each run: the page must not scroll sideways, the coach card must sit fully on screen, the
+tour must reach every stop it announces, and the page must raise no errors.
+"""
+
+import asyncio
+import functools
+import http.server
+import sys
+import threading
+from pathlib import Path
+
+from playwright.async_api import Browser, Locator, Page, async_playwright
+from playwright.async_api import TimeoutError as PlaywrightTimeoutError
+
+
+VIEWPORTS = {"phone": {"width": 375, "height": 740}, "desktop": {"width": 1280, "height": 800}}
+STOP_TIMEOUT_MS = 20_000
+
+MEASURE_JS = """(coach) => {
+  const de = document.documentElement;
+  const out = { scrollWidth: de.scrollWidth, clientWidth: de.clientWidth };
+  if (coach) {
+    const r = coach.getBoundingClientRect();
+    out.coach = [r.left, r.top, r.right, r.bottom].map(Math.round);
+    out.viewport = [innerWidth, innerHeight];
+  }
+  return out;
+}"""
+
+SETTLE_JS = """(el) => new Promise((resolve) => {
+  let last = '', same = 0, frames = 0;
+  const tick = () => {
+    const r = el.getBoundingClientRect();
+    const key = [r.left, r.top, scrollY].map(Math.round).join();
+    same = key === last ? same + 1 : 0;
+    last = key;
+    if (same >= 5 || ++frames > 180) resolve(); else requestAnimationFrame(tick);
+  };
+  tick();
+})"""
+
+
+class _QuietHandler(http.server.SimpleHTTPRequestHandler):
+    def log_message(self, format: str, *args: object) -> None:  # noqa: A002
+        pass
+
+
+def _serve(site: Path) -> http.server.ThreadingHTTPServer:
+    server = http.server.ThreadingHTTPServer(("127.0.0.1", 0), functools.partial(_QuietHandler, directory=str(site)))
+    threading.Thread(target=server.serve_forever, daemon=True).start()
+    return server
+
+
+async def _measure(page: Page, coach: Locator | None, where: str) -> list[str]:
+    handle = await coach.element_handle() if coach else None
+    m = await page.evaluate(MEASURE_JS, handle)
+    problems = []
+    if m["scrollWidth"] > m["clientWidth"]:
+        problems.append(f"{where}: page scrolls sideways (scrollWidth {m['scrollWidth']} > {m['clientWidth']})")
+    if coach:
+        left, top, right, bottom = m["coach"]
+        width, height = m["viewport"]
+        if left < 0 or top < 0 or right > width or bottom > height:
+            problems.append(f"{where}: coach at {m['coach']} is not inside the {width}x{height} viewport")
+    return problems
+
+
+async def _play_tour(page: Page, demo: str, play: str, where: str) -> list[str]:
+    coach = page.locator(f"{demo} .coach")
+    problems: list[str] = []
+    seen, total = 0, None
+    await page.click(play)
+    while total is None or seen < total:
+        try:
+            await page.locator(f"{demo} .coach.show").wait_for(timeout=STOP_TIMEOUT_MS)
+        except PlaywrightTimeoutError:
+            break
+        seen += 1
+        step = await coach.locator(".step").inner_text()
+        total = int(step.rsplit(" ", 1)[1])
+        await coach.evaluate(SETTLE_JS)
+        problems += await _measure(page, coach, f"{where} stop {seen}/{total}")
+        await coach.locator(".go").dispatch_event("click")
+    if total is None or seen < total:
+        problems.append(f"{where}: tour stalled after {seen} of {total or '?'} stops")
+    await page.wait_for_timeout(500)
+    problems += await _measure(page, None, f"{where} after the run")
+    return problems
+
+
+async def _check_page(browser: Browser, base: str, name: str, viewport: str) -> list[str]:
+    context = await browser.new_context(viewport=VIEWPORTS[viewport])
+    page = await context.new_page()
+    errors: list[str] = []
+    page.on("pageerror", lambda exc: errors.append(str(exc)))
+    await page.goto(f"{base}/demos/{name}/")
+    await page.wait_for_selector(".hw-demo .play, .hw-demo [data-el=hplay]")
+    where = f"{name} @ {viewport}"
+    problems = await _measure(page, None, f"{where} on load")
+    for demo_id in await page.eval_on_selector_all(".hw-demo[id]", "els => els.map(e => e.id)"):
+        demo = f"#{demo_id}"
+        if await page.locator(f"{demo} [data-el=hplay]").count():
+            problems += await _play_tour(page, demo, f"{demo} [data-el=hplay]", f"{where} {demo}")
+            continue
+        buttons = page.locator(f"{demo} .scenario-btn")
+        for i in range(await buttons.count()):
+            await buttons.nth(i).click()
+            label = await buttons.nth(i).inner_text()
+            problems += await _play_tour(page, demo, f"{demo} [data-el=play]", f"{where} {demo} '{label}'")
+    problems += [f"{where}: page error: {e}" for e in errors]
+    await context.close()
+    return problems
+
+
+def _demo_pages(site: Path) -> list[str]:
+    return sorted(p.parent.name for p in site.glob("demos/*/index.html") if 'class="hw-demo"' in p.read_text())
+
+
+async def _main(site: Path, pages: list[str]) -> int:
+    server = _serve(site)
+    base = f"http://127.0.0.1:{server.server_address[1]}"
+    async with async_playwright() as p:
+        browser = await p.chromium.launch()
+        jobs = [(n, v) for n in pages for v in VIEWPORTS]
+        results = await asyncio.gather(*(_check_page(browser, base, n, v) for n, v in jobs), return_exceptions=True)
+        await browser.close()
+    server.shutdown()
+    problems = []
+    for (name, viewport), result in zip(jobs, results, strict=True):
+        if isinstance(result, BaseException):
+            problems.append(f"{name} @ {viewport}: check crashed: {str(result).splitlines()[0]}")
+        else:
+            problems += result
+    for problem in problems:
+        sys.stdout.write(f"FAIL {problem}\n")
+    sys.stdout.write(f"{len(pages)} pages x {len(VIEWPORTS)} viewports checked, {len(problems)} problems\n")
+    return 1 if problems or not pages else 0
+
+
+if __name__ == "__main__":
+    site = Path(sys.argv[1])
+    sys.exit(asyncio.run(_main(site, _demo_pages(site))))