# Debugging investigation checklist

- Record environment, initial state, exact input and repeatable steps.
- Separate expected behavior from actual observations.
- Preserve a small failing fixture.
- List competing hypotheses and a distinguishing test.
- Inspect values, types, stack, request or computed style at the failing boundary.
- Change one relevant cause.
- Repeat the original reproduction and nearby edge cases.
- Confirm which build and environment were tested.
- Write a closure note with evidence and untested limits.
- Redact credentials and personal data before sharing evidence.