diff --git a/.github/workflows/pr-quality.yml b/.github/workflows/pr-quality.yml
index b6cc2d77..95364c96 100644
--- a/.github/workflows/pr-quality.yml
+++ b/.github/workflows/pr-quality.yml
@@ -27,6 +27,11 @@ jobs:
       - name: Install dependencies
         run: pip install requests pytest
 
+      - name: Install opa
+        uses: open-policy-agent/setup-opa@b2b258e089860efaadaaf71bf6e3aecb4a3eeff1 # v2.4.0
+        with:
+          version: 1.9.0
+
       - name: Run tests
         run: pytest tests/
 
diff --git a/tests/test_rego_examples.py b/tests/test_rego_examples.py
new file mode 100644
index 00000000..5613e856
--- /dev/null
+++ b/tests/test_rego_examples.py
@@ -0,0 +1,104 @@
+"""Every Rego policy shown in the docs must compile and follow Kosli's contract.
+
+A reader copies these. A block that does not compile wastes their time; one that
+compiles but never defines `allow` denies everything, which is worse because it
+looks like it worked.
+"""
+
+import os
+import re
+import shutil
+import subprocess
+import tempfile
+from pathlib import Path
+
+import pytest
+
+DOCS_ROOT = Path(__file__).resolve().parent.parent
+FENCE = re.compile(r"^[ \t]*```([a-zA-Z0-9_+-]*)([^\n]*)\n(.*?)^[ \t]*```", re.S | re.M)
+PACKAGE = re.compile(r"^\s*package\s+([A-Za-z_][\w.]*)", re.M)
+# A rule that can become true, so `default allow := false` on its own does not count.
+ALLOW_RULE = re.compile(r"^\s*allow\b(?!\s*:?=\s*false)", re.M)
+
+
+def _dedent(body):
+    indent = min(
+        (len(l) - len(l.lstrip()) for l in body.splitlines() if l.strip()), default=0
+    )
+    return "\n".join(l[indent:] if len(l) >= indent else l for l in body.splitlines())
+
+
+def rego_policies():
+    """Rego blocks a reader is meant to copy whole.
+
+    Two ways a block says that: it declares its own package, or its fence carries a
+    filename, as in ```rego pr-compliant.rego. Give a block a filename whenever the
+    page tells someone to create the file, and this will hold it to compiling.
+
+    Anything else is a fragment illustrating one rule. It cannot compile alone
+    because its inputs are unbound, so there is nothing here to check.
+    """
+    for path in sorted(DOCS_ROOT.rglob("*")):
+        if path.suffix not in (".md", ".mdx"):
+            continue
+        if "node_modules" in path.parts:
+            continue
+        text = path.read_text(encoding="utf-8")
+        for match in FENCE.finditer(text):
+            if match.group(1).lower() != "rego":
+                continue
+            filename = match.group(2).strip()
+            if filename and not filename.endswith(".rego"):
+                filename = ""  # a fence attribute, not a file the reader creates
+            body = _dedent(match.group(3))
+            package = PACKAGE.search(body)
+            if not package and not filename:
+                continue
+            line = text[: match.start()].count("\n") + 1
+            yield pytest.param(
+                body,
+                package.group(1) if package else None,
+                id=f"{path.relative_to(DOCS_ROOT)}:{line}",
+            )
+
+
+POLICIES = list(rego_policies())
+
+
+def test_the_docs_still_contain_rego_policies():
+    assert POLICIES, (
+        "no Rego policies found, so the checks below all pass without checking "
+        "anything; the fence pattern has stopped matching the docs"
+    )
+
+
+def _opa():
+    opa = shutil.which("opa")
+    if opa:
+        return opa
+    if os.environ.get("CI"):
+        pytest.fail("opa is not installed, so the Rego examples went unchecked")
+    pytest.skip("opa is not installed; install it to check the Rego examples")
+
+
+@pytest.mark.parametrize("body,package", POLICIES)
+def test_rego_policy_compiles(body, package):
+    opa = _opa()
+    with tempfile.TemporaryDirectory() as tmp:
+        policy = Path(tmp) / "policy.rego"
+        policy.write_text(body, encoding="utf-8")
+        result = subprocess.run(
+            [opa, "check", str(policy)], capture_output=True, text=True
+        )
+    assert result.returncode == 0, (result.stdout + result.stderr).strip()
+
+
+@pytest.mark.parametrize("body,package", POLICIES)
+def test_rego_policy_follows_the_kosli_contract(body, package):
+    # policy-reference/rego_policy.mdx: Kosli reads data.policy.allow, and exits 0
+    # when it is true and 1 when it is false.
+    assert package is not None, "is shown as a file to create but declares no package"
+    assert package == "policy", f"declares package {package}, so Kosli never reads it"
+    assert ALLOW_RULE.search(body), (
+        "defines no allow rule that can be true, so it denies everything"
+    )
diff --git a/tutorials/linking_trails_across_branches.md b/tutorials/linking_trails_across_branches.md
index 3294fe03..7ebae6ce 100644
--- a/tutorials/linking_trails_across_branches.md
+++ b/tutorials/linking_trails_across_branches.md
@@ -45,12 +45,14 @@ Use `kosli evaluate trail` on the main-branch build to evaluate the PR trail aga
         Use `kosli evaluate trail` to check the PR trail against a Rego policy. Create a policy file (e.g. `pr-compliant.rego`):
 
         ```rego pr-compliant.rego
-        package main
+        package policy
 
-        default allow = false
+        import rego.v1
 
-        allow {
-          input.trail.compliance.is_compliant == true
+        default allow := false
+
+        allow if {
+          input.trail.compliance_status.is_compliant == true
         }
         ```
 
@@ -70,7 +72,7 @@ Use `kosli evaluate trail` on the main-branch build to evaluate the PR trail aga
         ```bash
         IS_COMPLIANT=$(kosli get trail "$PR_TRAIL" \
           --flow app-pr \
-          --output json | jq -r '.compliance.is_compliant')
+          --output json | jq -r '.compliance_status.is_compliant')
         ```
 
         This is simpler but does not use a formal policy. You will need `$IS_COMPLIANT` in the next step.
@@ -258,7 +260,7 @@ Below is a simplified GitHub Actions workflow for a main-branch build that links
             run: |
               IS_COMPLIANT=$(kosli get trail "${{ steps.pr.outputs.trail }}" \
                 --flow app-pr \
-                --output json | jq -r '.compliance.is_compliant')
+                --output json | jq -r '.compliance_status.is_compliant')
 
               kosli attest generic \
                 --name pr-build-compliance \