diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 00000000..afc98c89
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,18 @@
+# CLAUDE.md
+
+**Do not edit this file.** Agents must never add, remove, or reword anything here. If a change seems needed, say so and let a human do it.
+
+## Ask before testing
+
+When asked to review code or build a feature, do not run the test suite and do not write new tests. Make the change, report it, then ask the user whether tests should be added — describing the tests you have in mind — and wait for the user to confirm.
+
+Two reasons this matters here: the suite takes minutes, and `tests/.snapshots/success.txt` plus the tally in `tests/Visual/Parallel.php` encode the whole suite's result, so a single added test breaks both.
+
+Once the user confirms:
+
+```bash
+composer test:unit         # fast, excludes the visual group
+composer test:integration  # visual and snapshot tests
+composer test              # everything CI runs, in CI's order
+composer update:snapshots  # only when a test was added or removed
+```