Lists multiple specific concrete actions via the four-phase process (investigate, analyze patterns, hypothesize, implement) and clearly describes the methodology as 'systematic root-cause investigation before any fix attempt.'

Clearly answers both 'what' (enforces systematic root-cause investigation using a four-phase process) and 'when' (explicit 'Use when...' clause with multiple trigger scenarios, plus a 'DO NOT TRIGGER' exclusion clause for additional clarity).

Excellent coverage of natural trigger terms users would encounter: 'bugs', 'test failures', 'build errors', 'unexpected behavior', 'performance problems', 'integration issues', 'quick fix', 'previous fix attempts have failed.' These are terms users naturally use when describing debugging scenarios.

Highly distinctive — focuses specifically on root-cause debugging methodology rather than general coding or fixing. The explicit exclusion of 'new feature development or refactoring without a known defect' further reduces conflict risk with other skills.

Extremely verbose at ~250+ lines. Extensive sections on rationalizations, red flags, 'human partner signals,' and motivational content ('systematic is faster than thrashing') are things Claude already knows or doesn't need repeated multiple ways. The 'When to Use' and 'Don't skip when' sections largely restate the same point. The 'Common Rationalizations' table and 'Red Flags' section overlap significantly.

The four-phase process provides a structured approach with some concrete examples (the multi-layer diagnostic bash script is good), but most guidance is procedural/philosophical rather than executable. Phases 2-4 are largely checklists of general advice ('Find working examples,' 'Form single hypothesis') rather than concrete, copy-paste-ready commands or code patterns.

The four-phase workflow is clearly sequenced with explicit gates between phases ('MUST complete each phase before proceeding'). Phase 4 includes validation steps (create failing test, verify fix, escalation after 3 failures), and there are clear feedback loops (return to Phase 1 if hypothesis fails, question architecture after 3+ failures).

References to supporting techniques (root-cause-tracing.md, defense-in-depth.md, condition-based-waiting.md) and related skills (kit:tdd, kit:verify) are clearly signaled and one level deep. The quick reference table provides a good overview, and detailed content is appropriately organized into phases.