Conciseness

The body is mostly efficient (it delegates detail to the reference rather than teaching REST concepts), but contains clear duplication that could be tightened: the Constraints section states the compile rule in prose ("Before applying any REST API changes, ensure the project compiles. If compilation fails, stop immediately.") and then repeats it in the MANDATORY and SAFETY bullets, and the 'When to use this skill' section re-lists the five trigger phrases verbatim from the frontmatter description. This matches the score-3 anchor 'mostly efficient but includes some unnecessary explanation or could be tightened' — not 4, since the redundancy is structural (whole duplicated sections), not just minor trimming.

Actionability

Concrete executable commands are given (`./mvnw compile` or `mvn compile`, `./mvnw clean verify` or `mvn clean verify`) and the exact reference path to read (`references/302-frameworks-spring-boot-rest.md`) is specified. This is mostly executable guidance with minor gaps: workflow steps 2–3 remain high-level ('Identify requested outcomes, constraints, and the minimum safe set of changes to apply') without concrete pointers into the reference's per-topic examples. Not score 3 because the commands and file references are fully concrete and executable, not pseudocode.

Workflow Clarity

The 4-step workflow (read reference → gather scope → apply changes → verify and report) is clearly sequenced with explicit validation checkpoints: MANDATORY compile before changes, SAFETY stop on failure, and VERIFY (full `clean verify`) after improvements, plus two EDGE CASE escalation rules. Not score 5 because there is no fix-and-retry feedback loop — failure handling is 'stop immediately' rather than error recovery — and steps 2–3 lack the checkpoint specificity of the score-5 anchor.

Progressive Disclosure

SKILL.md is a lean overview (coverage list, constraints, workflow) that appropriately pushes all detailed rules and code examples into a single reference file, which is well-signaled twice (Workflow step 1 and a dedicated '## Reference' section with a markdown link) and confirmed to be exactly one level deep with no nested references. This matches the score-5 anchor: clear overview, well-signaled one-level-deep reference, easy navigation.

Specificity

The description names concrete actions ("design, review, or improve REST APIs with Spring Boot") and comprehensively enumerates specific coverage areas: "HTTP methods, resource URIs, status codes, DTOs, versioning, deprecation and sunset headers, content negotiation (JSON and vendor media types), ISO-8601 instants in DTOs, pagination/sorting/filtering, Bean Validation at the boundary, idempotency, ETag concurrency, HTTP caching, error handling, security, contract-first OpenAPI (OpenAPI Generator), controller advice, and problem details for errors". Every item is concrete domain capability, not fluff, and no gaps in coverage of the REST API design surface. Not score 4 because coverage goes beyond 'several specific actions with minor gaps' — it is comprehensive.

Completeness

It explicitly answers 'what' ("design, review, or improve REST APIs with Spring Boot — including HTTP methods, resource URIs, status codes, DTOs...") and 'when' with an explicit "Use when you need to..." clause plus a second explicit trigger sentence ("This should trigger for requests such as...") with concrete trigger phrases. This matches the score-5 anchor exactly; score 4 would require the 'when' to be less explicit than these literal user-facing trigger sentences.

Trigger Term Quality

Explicit natural trigger phrases are listed verbatim: "Review Java code for Spring Boot REST API; Apply best practices for Spring Boot REST API in Java code; Design Spring Boot REST controllers and DTOs; Add Problem Details error responses in Spring Boot REST; Improve pagination validation or idempotency in Spring APIs" — these are exactly the phrasings a user would naturally say, covering review, design, and improvement intents plus specific sub-topics. Not score 4 because the natural-term coverage is comprehensive rather than missing 'a few natural terms'.

Distinctiveness Conflict Risk

The niche is clear and specific ("REST APIs with Spring Boot", "OpenAPI Generator", "RFC 7807 problem details"), so it would not trigger for unrelated skills. However, "Part of Plinth Toolkit" signals a family of sibling skills (e.g., other Spring/Java skills in the same toolkit), creating minor overlap risk with closely related skills — matching the score-4 anchor 'mostly distinct; minor overlap risk with closely related skills' rather than score 5's 'minimal conflict risk'.