The body is lean and imperative throughout, assuming Claude's competence — it never explains known concepts like OODA, stack traces, or sequence diagrams, and every line carries actionable guidance.

Steps are concrete and specific ('git diff', 'add diagnostic logging at each boundary', 'State one clear hypothesis: X is the root cause because Y', 'smallest possible change... one variable at a time'); though code-free, this is an instruction-only skill whose guidance is actionable, which the rubric does not penalize.

Four sequentially labeled phases with a validation_checklist, explicit verification and regression checks in implementation, and clear feedback loops ('If fails, form a new hypothesis — don't stack fixes'; 'If 3+ fixes failed: stop... question the architecture').

A single self-contained file organized into clearly labeled sections (role, when_to_use_skill, core_concepts, four phases, validation_checklist, best_practices, pitfalls) with no nested external references, which is appropriate for a cohesive single-workflow skill with no bundle files.

Names the debugging domain and actions ('investigate errors, test failures, and unexpected behavior', 'root cause before fix') but does not list multiple distinct concrete actions, matching the 'domain and some actions' anchor rather than the comprehensive level 3.

It states what the skill does (investigate errors, root cause) but lacks an explicit 'Use when...' trigger clause; per the guidelines, a missing when clause caps completeness at 2.

'errors, test failures, and unexpected behavior' are natural user terms, but common variations like 'bug', 'debug', 'crash', or 'stack trace' are missing, so coverage is partial rather than full.

The 'root cause before fix' framing is a distinct debugging niche, but the broad triggers ('errors, test failures, unexpected behavior') could overlap with other engineering skills, so it is only somewhat specific.