diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
index b5e77cc..b7901ba 100644
--- a/.github/workflows/docs.yml
+++ b/.github/workflows/docs.yml
@@ -26,6 +26,8 @@ jobs:
         run: python tools/build_docs.py
       - name: Build the site (broken links fail)
         run: mkdocs build --strict
+      - name: Every page is rendered, not raw Markdown
+        run: python tools/check_site.py
       - uses: actions/upload-pages-artifact@v3
         if: github.event_name == 'push'
         with:
diff --git a/mkdocs.yml b/mkdocs.yml
index 5c25314..c144e86 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -20,6 +20,8 @@ plugins:
 
 markdown_extensions:
   - admonition
+  - attr_list
+  - md_in_html
   - tables
   - toc:
       permalink: true
diff --git a/tools/check_site.py b/tools/check_site.py
new file mode 100644
index 0000000..bf03c36
--- /dev/null
+++ b/tools/check_site.py
@@ -0,0 +1,37 @@
+"""Fail if a built page still shows Markdown source, which means it was not rendered.
+
+    python tools/check_site.py        # after `mkdocs build`
+"""
+
+from __future__ import annotations
+
+import re
+import sys
+from pathlib import Path
+
+SITE = Path(__file__).resolve().parents[1] / "build" / "site"
+
+#: Markdown that survives only when a page was left unprocessed.
+RAW_MARKDOWN = ("| --- |", "](")
+CODE = re.compile(r"<(pre|code)\b.*?</\1>", re.S)
+TAG = re.compile(r"<[^>]+>")
+
+
+def unrendered(page: Path) -> list[str]:
+    text = TAG.sub("", CODE.sub("", page.read_text()))
+    return [marker for marker in RAW_MARKDOWN if marker in text]
+
+
+def main() -> int:
+    pages = sorted(SITE.rglob("index.html"))
+    if not pages:
+        sys.exit(f"no pages under {SITE}; run mkdocs build first")
+    bad = {str(page.relative_to(SITE)): found for page in pages if (found := unrendered(page))}
+    for page, found in bad.items():
+        print(f"unrendered Markdown {found} in {page}")
+    print(f"checked {len(pages)} pages, {len(bad)} unrendered")
+    return 1 if bad else 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())