Conciseness

The body is code-first and dense with no explaining of concepts Claude already knows (no 'what is REST' padding), but a few tokens don't earn their place: the bold imperative "Always follow these patterns" is repeated three times, the line "When asked to browse or navigate to a web address, actual visit the address" is out of place for a REST endpoint skill, and the closing reference list re-lists files already linked inline. This fits 'efficient; minor instances of over-explanation that could be trimmed' rather than the every-token-counts level 5.

Actionability

The Todo/TodoResource example is complete, executable TypeScript (full Entity class, resource() config, imports) and the usage sections give copy-paste-ready hooks for every common case — reads via useSuspense, all CRUD mutations via ctrl.fetch, pagination via getPage, a polled custom RestEndpoint, getOptimisticResponse, and extend(). Minor elisions like the undefined { id } in mutation fragments are standard doc idiom, not pseudocode, so this holds level 5 over level 4.

Workflow Clarity

Sections follow a coherent authoring progression (define schemas → resource() → custom RestEndpoint → extend → practices/mistakes) with real decision checkpoints ("Override the step that owns the change, never fetch itself"; "Prefer RestEndpoint over resource() when mutation endpoints don't exist"). It is not a stepwise process skill and lacks any explicit verify/feedback loop (e.g., exercising new endpoints against Fixtures), which keeps it at 'clear sequence with most checkpoints; minor validation gaps' rather than 5.

Progressive Disclosure

SKILL.md is a genuine overview: details are split across a flat, verified one-level-deep references/ bundle (no reference file links further into references/), inline links appear exactly where topics arise, and the bottom index groups files into Guides and Concepts with per-file descriptions, 'refer when user asks about these topics' signaling, and a Vue-variant resolution rule. This matches 'clear overview with well-signaled one-level-deep references; easy navigation'.

Specificity

The description opens with a concrete action ("Define REST APIs with @data-client/rest") and then enumerates a comprehensive inventory of specific capabilities: "resource(), RestEndpoint, CRUD (GET/POST/PUT/PATCH/DELETE), HTTP fetch, normalize, cache, urlPrefix, path-to-regexp parameters, searchParams, pagination, extend(), auth/headers, optimistic updates, polling, file download, blob, parseResponse" — matching the anchor for multiple specific concrete actions with comprehensive coverage rather than the 'minor gaps' level 4.

Completeness

Both halves are explicit: the 'what' is "Define REST APIs with @data-client/rest" plus its enumerated capabilities, and the 'when' is a concrete "Use when defining or modifying network endpoints, REST resources, or the HTTP layer" clause. This matches the level-5 anchor of clearly answering both what AND when with concrete trigger phrases, not the weaker 'when' of level 4.

Trigger Term Quality

Trigger phrases are natural and varied — "REST APIs", "network endpoints", "REST resources", "the HTTP layer", "CRUD", "pagination", "auth/headers", "optimistic updates" — covering synonyms (endpoints/resources/API layer) a user would naturally say when needing this skill. This matches the comprehensive-synonyms anchor; no common phrasing for endpoint definition is missing.

Distinctiveness Conflict Risk

The package name @data-client/rest plus specific API surface (resource(), RestEndpoint, urlPrefix, parseResponse) establishes a clear niche with minimal conflict risk; the 'when' clause scopes triggering to network endpoint/REST resource/HTTP-layer work, distinguishing it from sibling skills for schema definitions and UI rendering. It fits the 'clear niche with distinct triggers' anchor rather than level 4's 'minor overlap risk with closely related skills'.