Conciseness

The body is mostly efficient - a compact category list with inline expected status codes, a dense anti-patterns table, and brief Limitations - but the Overview re-explains the happy-path vs. rejection-path concept Claude already knows ('A typical test suite has a happy-path test for every endpoint... What's missing is the rejection path'), and the ~60-line worked example demonstrates four categories where two or three would carry the pattern. Minor instances of over-explanation that could be trimmed fits anchor 4; not 5 because those tokens are not all earning their place, not 3 because there is no padded or unnecessary library-style explanation.

Actionability

Fully executable guidance: a complete pytest worked example with parameterized tables carrying exact expected statuses and fields, per-category expected status codes spelled out (401, 403/404, 429, 409/412/422, 502/503/504), a concrete output-format template with a per-category count table, and a verified reference catalog (references/negative-path-catalog.md) containing per-pattern test tables and copy-ready CWE-tagged starter payloads for all seven categories. Specific examples cover the common cases, matching anchor 5; fixture imports (tests.fixtures, tests.payloads) are project context, not a gap.

Workflow Clarity

The process is well structured - a category checklist, a worked example, an output contract with per-category counts and skipped-category rationale, and an explicit validation feedback loop ('Run the new negative tests; expect all to pass... Any failure indicates a real gap - either the validator is missing the case OR the assertion is wrong'). Score 4 rather than 5 because the top-level sequence (identify happy-path tests, declare input domain, generate, emit, run) is implicit rather than numbered, and the prerequisite input-domain declaration step is only surfaced in Limitations; score above 3 because verification and error-recovery checkpoints are explicitly present, and the batch/destructive cap does not apply since the skill generates test code rather than performing batch mutations.

Progressive Disclosure

Verified against the actual bundle: exactly one reference file (references/negative-path-catalog.md), it exists, is one level deep, and is clearly signaled in the body with a descriptive link stating precisely what it holds ('Per-pattern test tables and the starter adversarial-payload catalog (with CWE / OWASP references)'). The split is appropriate - per-pattern tables and payload starters live in the reference while the body keeps the overview, one worked example, and the output contract - and body sections are clearly headed, matching anchor 5.

Specificity

Enumerates several concrete actions - 'input validation rejection, missing required fields, type mismatches, authorization failures, rate-limit errors, and adversarial payloads from the malicious-payload-bank, emitted as parameterized tests in the project's runner format' - plus concrete scenarios like 'a batch endpoint that must apply all rows or none, optimistic-concurrency version conflicts'. Score 4 rather than 5 because the enumeration skips authentication (401) failures, conflict/state errors, and server errors that the skill itself covers, a minor coverage gap matching the anchor-4 example.

Completeness

Explicitly answers both questions: the 'what' is 'produces companions exercising input validation rejection, missing required fields, type mismatches, authorization failures, rate-limit errors, and adversarial payloads... emitted as parameterized tests in the project's runner format', and the 'when' is a concrete explicit clause: 'Use when code has deliberate error paths and the suite only proves the success case.' Both are present, explicit, and concrete, matching anchor 5 rather than the vaguer 'when' of anchor 4.

Trigger Term Quality

Contains good natural keywords users would say - 'happy-path test', 'error paths', 'success case', 'input validation', 'rate-limit' - but the single most natural phrase for this skill ('negative tests') never appears, nor do common synonyms like 'edge cases', 'failure cases', or 'error handling'. Good coverage with a few natural terms missing fits anchor 4; not 3 because far more than 'some' relevant keywords are present, not 5 because key synonyms are absent.

Distinctiveness Conflict Risk

The niche is clearly carved - generating rejection-path companions for existing happy-path tests, with triggers like 'the suite only proves the success case' - making it mostly distinct. Score 4 rather than 5 because it overlaps with closely related testing skills the ecosystem provides (boundary-value-generator, general test writing, gherkin-from-stories), and the description does not state its boundary against them.