Conciseness

The body is ~35 lines of dense, rule-style bullets with zero padding — it never explains what BDD/TDD are beyond a one-line framing ('Same red → green → refactor rhythm as TDD, oriented around user-facing outcomes') and every token carries a project-specific rule Claude could not infer. This matches the 'lean and efficient; assumes Claude's competence' anchor; a 4 would require noticeable over-explanation that is absent.

Actionability

Guidance is concrete and executable in the instruction-only sense: exact APIs ('`describe` / `it` from `bun:test` (not `test`)', 'describe.each / it.each', 'beforeAll / beforeEach'), a concrete path convention ('test/support/ modules that export functions'), and a measurable policy ('a few happy paths plus one or two errors'). It falls short of the top anchor because there is no copy-paste-ready example (e.g., a minimal describe/it block showing the required root-describe layout), which is the one gap for an instruction-only skill.

Workflow Clarity

The core sequence is named ('concrete examples of desired behaviour first, then implement until they pass... refactor is required after green') but the checkpoints are implicit — it never states how to verify green (e.g., run `bun test` and see failures before/after), matching 'sequence present but checkpoints missing or implicit'. Not a 4 because no explicit verification step or feedback loop (fail → fix → re-run) is spelled out; not a 2 because the rhythm and its ordering are clearly stated.

Progressive Disclosure

The skill is under 50 lines with well-organized sections (Test files, Testing library code) and no content that warrants external files; the single 'See also: `repo-conventions`' pointer is one level deep and clearly signaled. Per the rubric's simple-skill guidance this matches the top anchor.

Specificity

The description lists several concrete capabilities — 'scenario-oriented examples, describe/it layout rules, library-integration testing, and no Cucumber' — which map directly to the skill's actual scope. It stops short of comprehensive coverage (no mention of the refactor requirement or shared-helper conventions), matching the 'several specific actions; minor gaps' anchor rather than the fully comprehensive anchor above.

Completeness

It explicitly answers both parts: what it does ('BDD-first testing with bun:test in this repository — scenario-oriented examples, describe/it layout rules, library-integration testing, and no Cucumber') and when to use it ('Use when writing or changing tests, adding fixtures, mocking libraries, or when the user mentions BDD, TDD, bun:test, or Vitest'). This matches the top anchor with concrete trigger phrases, so a 4's 'when could be more explicit' does not apply.

Trigger Term Quality

Triggers cover natural phrasings users would say — 'writing or changing tests, adding fixtures, mocking libraries' — plus synonyms and adjacent tool names 'BDD, TDD, bun:test, or Vitest', comprehensively covering the domain's natural vocabulary (including the Vitest disambiguation). Not a 4 because no common variation of how a user would request this work is conspicuously missing.

Distinctiveness Conflict Risk

The niche is clear — repo-scoped BDD with bun:test, with an explicit exclusion ('no Cucumber') that sharpens boundaries. It does not hit the top anchor because triggering on 'TDD' and 'Vitest' creates minor overlap risk with a generic TDD skill or a true Vitest skill, fitting the 'mostly distinct; minor overlap risk with closely related skills' anchor.