Diagnose

A six-phase loop for systematic bug investigation. The key insight: invest disproportionate effort in Phase 1. With a reliable feedback loop, phases 2–6 become mechanical.

When to use this skill

• Hard bugs that resist quick fixes
• Performance regressions with unclear root cause
• Flaky failures that need repeated-run evidence
• Any failure where previous fix attempts failed

When not to use this skill

• Quick targeted fixes with obvious root cause → use debugging
• Symptom-first log triage → use log-analysis
• Broad test-policy design → use testing-strategies

The Six Phases