Conciseness

The body is mostly terse tables and code, but it restates HTTP basics Claude already knows (the Method Semantics table with GET/Safe/Idempotent, and a Status Code Reference explaining e.g. '404 Not Found — Resource doesn't exist'), and three full language implementations (TypeScript, Django, Go) duplicate the same create-with-validation pattern. That fits 'mostly efficient but includes some unnecessary explanation or could be tightened' rather than the score-4 anchor, since trimming the basics and two of the three implementations would lose little.

Actionability

Guidance is fully executable: copy-paste-ready Zod/Next.js and DRF examples with Location headers and field-level error details, concrete SQL for cursor pagination ('LIMIT 21; -- fetch one extra to determine has_next'), exact JSON envelopes, and specific URL/query syntax. The common cases are covered; only the Go snippet's undefined helpers (writeError, writeJSON) are a minor gap, so it sits at the score-5 anchor rather than dropping to 4.

Workflow Clarity

'When to Activate' scopes usage and the closing 'API Design Checklist' ('Before shipping a new endpoint: ...') provides an explicit validation gate covering naming, status codes, auth, and leak prevention. However, this is a reference/patterns skill with no multi-step sequence or error-recovery feedback loop, so it matches 'clear sequence with most checkpoints; minor validation gaps' better than the score-5 anchor's explicit validate-fix-retry workflow.

Progressive Disclosure

No bundle files exist (no references/, scripts/, or assets/), and roughly 500 lines — including three language-specific implementation examples and detailed filtering/sorting syntax — are all inlined in SKILL.md where a split into reference files belongs. Section headers are clear (so not the score-2 'minimal structure' case), but this is squarely 'some structure... content that should be separate is inline'.

Specificity

Lists several concrete subtopics ("resource naming, status codes, pagination, filtering, error responses, versioning, and rate limiting") with near-comprehensive coverage of the domain, but they are stated as topics rather than actions (no verbs like 'Designs' or 'Returns'), matching the 'several specific actions; minor gaps' anchor rather than the fully comprehensive score-5 anchor.

Completeness

The 'what' is clear (REST API design patterns with an enumerated scope), but there is no 'Use when...' clause or equivalent explicit trigger guidance — 'for production APIs' only weakly implies when — and the judging guidelines cap completeness at 3 in that case. It is not a 4 because the 'when' is absent rather than merely imprecise.

Trigger Term Quality

Natural terms users would say are well covered — "REST API", "pagination", "status codes", "rate limiting", "versioning", "error responses" — but a few common variants are missing ("endpoints", "RESTful", "API contract"), which fits 'good keyword coverage; a few natural terms missing' rather than the comprehensive score-5 anchor.

Distinctiveness Conflict Risk

The enumerated scope ("resource naming, status codes, pagination, filtering, error responses, versioning, and rate limiting") establishes a clear, mostly distinct niche, but there is minor overlap risk with closely related skills such as OpenAPI/Swagger documentation or general backend-development skills, matching the score-4 anchor rather than the minimal-conflict score-5 anchor.