diff --git a/tests/mkdocs_hooks_test.py b/tests/mkdocs_hooks_test.py
new file mode 100644
index 0000000..c668516
--- /dev/null
+++ b/tests/mkdocs_hooks_test.py
@@ -0,0 +1,120 @@
+"""Tests for the redirect stubs ``scripts/mkdocs_hooks.py`` writes after a build.
+
+Run them with the rest of the suite::
+
+    pytest tests/
+"""
+
+from __future__ import annotations
+
+import importlib.util
+from pathlib import Path
+
+import pytest
+
+HOOKS_PATH = Path(__file__).parent.parent / "scripts" / "mkdocs_hooks.py"
+
+# ``scripts/`` is not a package: MkDocs loads the hook by path, and so does this.
+_spec = importlib.util.spec_from_file_location("mkdocs_hooks", HOOKS_PATH)
+assert _spec is not None and _spec.loader is not None
+hooks = importlib.util.module_from_spec(_spec)
+_spec.loader.exec_module(hooks)
+
+
+def _build(tmp_path: Path, site_url: str | None) -> Path:
+    site = tmp_path / "site"
+    site.mkdir()
+    hooks.on_post_build({"site_dir": str(site), "site_url": site_url})
+    return site
+
+
+def _target(stub: Path) -> str:
+    """The URL a stub sends the browser to."""
+    text = stub.read_text(encoding="utf-8")
+    start = text.index('var target = "') + len('var target = "')
+    return text[start : text.index('"', start)]
+
+
+@pytest.fixture
+def not_netlify(monkeypatch):
+    monkeypatch.delenv("NETLIFY", raising=False)
+
+
+def test_every_retired_and_legacy_url_gets_a_stub(tmp_path, not_netlify):
+    site = _build(tmp_path, "https://commit-check.com/")
+
+    for old, target in hooks.MOVED_URLS.items():
+        assert (
+            _target(site / old / "index.html") == f"https://commit-check.com/{target}"
+        )
+    for legacy, target in hooks.LEGACY_URLS.items():
+        assert _target(site / f"{legacy}.html") == f"https://commit-check.com/{target}"
+
+
+def test_a_stub_redirects_three_ways_and_keeps_the_fragment(tmp_path, not_netlify):
+    site = _build(tmp_path, "https://commit-check.com/")
+    text = (site / "rules.html").read_text(encoding="utf-8")
+
+    url = "https://commit-check.com/rules/"
+    assert f'<link rel="canonical" href="{url}">' in text
+    assert f'<meta http-equiv="refresh" content="0; url={url}">' in text
+    # The script, not the meta refresh, is what carries ``#cc003`` across.
+    assert "location.replace(target + location.hash)" in text
+    assert f'<a href="{url}">{url}</a>' in text
+
+
+def test_a_site_url_without_a_trailing_slash_still_joins(tmp_path, not_netlify):
+    # Deploy previews pass their own URL in, sometimes without the slash.
+    site = _build(tmp_path, "https://deploy-preview-7--commit-check.netlify.app")
+
+    assert _target(site / "rules.html") == (
+        "https://deploy-preview-7--commit-check.netlify.app/rules/"
+    )
+
+
+def test_without_a_site_url_the_targets_are_root_relative(tmp_path, not_netlify):
+    site = _build(tmp_path, None)
+
+    assert _target(site / "rules.html") == "/rules/"
+    assert _target(site / "projects" / "index.html") == "/"
+
+
+def test_on_netlify_only_the_retired_pages_get_stubs(tmp_path, monkeypatch):
+    # netlify.toml redirects the .html URLs; a stub there would shadow
+    # rules/index.html and loop.
+    monkeypatch.setenv("NETLIFY", "true")
+    site = _build(tmp_path, "https://commit-check.com/")
+
+    for old in hooks.MOVED_URLS:
+        assert (site / old / "index.html").is_file()
+    assert not any(site.glob("*.html"))
+
+
+def test_a_stub_never_overwrites_a_page_the_build_wrote(tmp_path, not_netlify):
+    # The stubs run after the build, so a retired URL that became a real page
+    # again would be replaced by a redirect away from itself.
+    site = tmp_path / "site"
+    site.mkdir()
+    page = site / "guides" / "pre-commit" / "index.html"
+    page.parent.mkdir(parents=True)
+    page.write_text("real page", encoding="utf-8")
+
+    hooks.on_post_build(
+        {"site_dir": str(site), "site_url": "https://commit-check.com/"}
+    )
+
+    assert page.read_text(encoding="utf-8") == "real page"
+
+
+def test_no_stub_redirects_to_another_stub():
+    # A chain would cost a second hop, and a cycle would never end.
+    retired = {f"{old}/" for old in hooks.MOVED_URLS}
+    for target in [*hooks.MOVED_URLS.values(), *hooks.LEGACY_URLS.values()]:
+        assert target not in retired, target
+
+
+def test_the_pages_the_cli_links_to_never_move():
+    # Every released commit-check prints commit-check.com/rules/#ccNNN, and
+    # links to configuration/; those two pages must stay where they are.
+    assert "rules" not in hooks.MOVED_URLS
+    assert "configuration" not in hooks.MOVED_URLS