Conciseness

The 26-line body is lean and every sentence instructs rather than explains: 'Write one test for one behavior. Use a clear name and the real code, not mocks' and 'If it passes, it tests nothing new: change the test'. It assumes Claude's competence (no explanation of what TDD is, what tests are, or why they matter), matching the anchor 'every token earns its place'; no trimming is possible without losing guidance.

Actionability

The guidance is concrete and executable for an instruction-only skill: each cycle step names the action and its guard ('The test must fail because the behavior is missing, not because of a typo or a missing import'), and rules like 'A bug fix starts with a test that reproduces the bug' are directly followable. It stops short of level 5 because there are no inline examples or commands — e.g., no sample test name or a way to discover the project's test command — leaving minor gaps even though detail is properly delegated to references/writing-good-tests.md.

Workflow Clarity

The five-step cycle is clearly sequenced with explicit validation checkpoints ('Watch it fail', 'Watch it pass. Run the full suite'), a feedback loop for error recovery ('If it passes, it tests nothing new: change the test'), and a completion checklist ('Before you say it is done'). This matches the level-5 anchor — explicit validation steps, feedback loops, and a checklist; this is not a destructive/batch operation so no cap applies.

Progressive Disclosure

The body is a clear overview of the process, and the single detail file is well-signaled at the exact point of need ('When writing or changing a test, read references/writing-good-tests.md'). The referenced file exists and is one level deep — it contains no further references or links — so navigation is trivial. This matches both the under-50-lines exception (well-organized sections suffice) and the clear-overview-with-one-level-references anchor.

Specificity

The description lists a full sequence of concrete actions — "write one failing test, run it and watch it fail, write the minimal code to pass, then refactor with the tests green" — comprehensively covering the skill's scope with no vague filler. It matches the anchor for multiple specific concrete actions with comprehensive coverage; the level-4 anchor's 'minor gaps in coverage' does not apply since the entire TDD cycle is enumerated.

Completeness

It explicitly answers both questions: 'what' is the concrete test-first implementation cycle, and 'when' is the explicit trigger clause naming concrete trigger phrases ("a new feature, a bug fix, or a behavior change"). This directly matches the level-5 anchor exemplar structure (what + explicit 'Use when' with concrete triggers); level 4's 'when could be more explicit' does not apply.

Trigger Term Quality

"Use when a change alters code behavior: a new feature, a bug fix, or a behavior change" provides good, natural keyword coverage of phrases users actually say. It falls short of level 5 because common variations and synonyms are missing (e.g., 'add a feature', 'fix an issue', 'implement X'), and 'whether the request comes alone or through delivery-flow' reads as internal jargon users would not naturally say.

Distinctiveness Conflict Risk

The 'what' (test-first development) is a distinct niche, but the trigger condition — "a change alters code behavior: a new feature, a bug fix, or a behavior change" — is broad enough to match nearly any development request, creating real overlap risk with general coding and review skills. It is somewhat specific but could still fire for similar skills, matching the level-3 anchor; level 4 requires only minor overlap with closely related skills, which this breadth exceeds.