Conciseness

The body is dense with skill-specific material (category catalog with expected status codes, worked example, output template, anti-patterns, limitations) with no padded explanation of known concepts. Minor trimmable spots: the Overview framing paragraph and the worked example partially duplicating the output-format template. Not 3: nothing explains concepts Claude already knows.

Actionability

The worked example is fully executable pytest — parametrize tables, fixtures, structured assertions like `expected_field in response.json().get('errors', {})` — and every category carries exact expected status codes (400/401/403/409/429), with a concrete output template. Copy-paste ready and covers the common cases.

Workflow Clarity

The flow (happy-path test → generate per 7 categories → emit report → run tests → diagnose) is clear and "Any failure indicates a real gap - either the validator is missing the case OR the assertion is wrong" provides a validation checkpoint with diagnosis guidance. Not 5: there is no explicit fix-and-re-run feedback loop. Validation exists, so the batch-operation cap at 3 does not apply.

Progressive Disclosure

The body stays a clear overview while the bulk per-pattern tables and the CWE/OWASP payload catalog are split into references/negative-path-catalog.md (verified to exist), linked once with a clear signal. One-level-deep, well-signaled reference with easy navigation.

Specificity

"generates parameterized tests for validation errors, missing fields, wrong types, authorization failures, rate limits, conflicts and attack payloads in the project's test runner format" lists multiple concrete actions covering the full failure-mode space. Not 4: coverage is comprehensive rather than having minor gaps.

Completeness

Explicitly answers both: when — "Use when code has deliberate error paths but the tests only prove the success case" (a concrete trigger condition), and what — "generates parameterized tests for... in the project's test runner format". Not 4: the when-clause is specific and concrete, not just present.

Trigger Term Quality

Natural phrases like "happy-path test", "error paths", "tests only prove the success case", "rate limits", and "attack payloads" are present, but the most common user phrasing "negative tests" (and synonyms like "failure cases" / "sad path") is missing. Not 3: several genuinely natural trigger phrases exist.

Distinctiveness Conflict Risk

Clear niche (negative companions for existing happy-path tests) with a distinctive trigger, but "attack payloads" and "rate limits" create minor overlap with security-testing and load-testing skills. Not 5: a couple of closely related skills could compete for the same trigger phrasing.