---

name: systematic-debugging description: Use when encountering any bug, test failure, or unexpected behavior — before proposing fixes.

Systematic Debugging

Four Phases

Phase 1: Reproduce

• Get a minimal, reliable reproduction
• Never fix what you can't reproduce

Phase 2: Understand

• Read the error message fully — the answer is often there
• Trace the call path from symptom to root cause
• Check: recent changes, environment differences, assumptions about inputs

Phase 3: Hypothesize

• Form 1-3 specific hypotheses about root cause
• Test each hypothesis with the smallest possible change
• Never change multiple things at once

Phase 4: Fix and Verify

• Fix the root cause, not the symptom
• Run the reproduction case — confirm fixed
• Run full test suite — confirm no regressions
• Invoke hotl:verification-before-completion

Red Flags

• "Let me try X and see what happens" without a hypothesis
• Changing multiple things before verifying
• Marking done without running full tests