Conciseness

The body is 11 lines with no padding and no explanation of concepts Claude already knows (it never explains what TDD or testing is); every token earns its place, matching the "lean and efficient" anchor.

Actionability

Each step is a concrete, executable directive with the key details specified — "Use a clear name and the real code, not mocks", "The test must fail because the behavior is missing, not because of a typo or a missing import", "Add nothing the test does not need". Per the scoring note, absence of code in an instruction-only skill is not penalized when guidance is this actionable.

Workflow Clarity

The five steps are clearly sequenced with explicit validation checkpoints and feedback loops: verify the failure is for the right reason (step 2), confirm the test isn't vacuous ("If it passes, it tests nothing new: change the test"), and run the full suite after both green and refactor (steps 4-5).

Progressive Disclosure

The body itself is well-organized, but the bundle contains references/writing-good-tests.md (~200 lines of test-writing guidance with mock/assertion rules) that the body never mentions — a reference that is present in the bundle but not signaled from SKILL.md, matching the anchor "references present but not clearly signaled". The under-50-line exception doesn't apply cleanly because an external reference exists and is orphaned.

Specificity

The description lists the complete TDD cycle as concrete actions — "write one failing test, run it and watch it fail, write the minimal code to pass, then refactor with the tests green" — which is comprehensive coverage within its domain, matching the top anchor rather than the 'minor gaps' of a 4.

Completeness

It explicitly answers both questions: what ("Implements a feature or bug fix test-first: write one failing test... refactor with the tests green") and when ("Use when a change alters code behavior: a new feature, a bug fix, or a behavior change"), with concrete trigger phrases — the exact shape of the anchor-5 example.

Trigger Term Quality

Natural phrases like "a new feature, a bug fix, or a behavior change" are present and would be said by users, but common synonyms such as "TDD", "test-driven", or "unit tests" are missing, and "delivery-flow" is internal jargon — good coverage with a few natural terms missing, so a 4 rather than 5.

Distinctiveness Conflict Risk

The test-first methodology is a clear niche distinct from other skills, but the trigger fires on any change that alters code behavior, which is broad enough to overlap with general coding and code-review skills — mostly distinct with minor overlap risk.