Conciseness

The ~45-line body is lean with no padding and no explanation of concepts Claude already knows, but the contract-vs-implementation distinction is repeated in three places ("不适用场景", "这个 skill 关注的是...不是...", "如果问题已经进入服务分层...切到 backend-microservice-development", and again in 延伸阅读), which is trimmable. Not 5 because of that repeated framing; not 3 because the body is otherwise efficient and assumes competence.

Actionability

Some concrete guidance exists — the caller-based prefix decision ("再决定 /user/、/service/、/build/、/open/ 等路径前缀") and the resource-semantics-over-actions rule — but no concrete examples: no good-vs-bad path pair, no sample error-code or pagination format, despite naming "错误码、分页格式" as in-scope. This matches 'some concrete guidance but incomplete; missing key details' rather than level 4's 'concrete code or commands with minor gaps'.

Workflow Clarity

"快速指导" provides a 5-step sequenced process (identify caller → choose prefix → design the contract as a set → prefer resource semantics → hand off to the sibling skill), but there are no validation checkpoints, e.g. an explicit step to review the finished contract against the "关键陷阱" list. Sequence present with checkpoints missing matches anchor 3; this is design guidance, not a destructive/batch operation, so the cap rule does not apply, but level 4 requires most checkpoints present.

Progressive Disclosure

The skill is under 50 lines with no bundle files, and the content is well organized into clearly labeled sections (适用场景 / 不适用场景 / 快速指导 / 高信号规则 / 关键陷阱 / 延伸阅读). The two cross-skill pointers ("backend-microservice-development", "common-technical-practices") are one level deep and clearly signaled, so the simple-skill exception for a 5 applies.

Specificity

The description enumerates multiple concrete design actions — "Resource 路径设计、HTTP 方法选择、请求响应对象、错误码和版本策略" — which comprehensively covers the API-contract design domain, matching the 'comprehensive coverage' anchor. It is not the level below (4) because there are no notable gaps in coverage of what contract design entails.

Completeness

It explicitly answers both questions: what it does ("设计 BK-CI API 契约...Resource 路径设计、HTTP 方法选择、请求响应对象、错误码和版本策略") and when to use it with concrete trigger phrases ("设计 BK-CI API 契约时使用" and "当用户要定义接口而不是实现业务逻辑时优先使用"). Not 4, because the 'when' is explicit and specific rather than something that 'could be more explicit'.

Trigger Term Quality

Natural terms a user would say are present — "API 契约", "接口", "Resource", "HTTP 方法", "错误码", "版本" — giving good keyword coverage. It falls short of 5 because common synonyms like "REST", "RESTful", "endpoint", or "OpenAPI" are absent.

Distinctiveness Conflict Risk

The BK-CI-specific domain plus the explicit carve-out "当用户要定义接口而不是实现业务逻辑时" gives it a clear niche with minimal conflict risk against implementation-focused skills. Not 4, because the scope boundary is stated explicitly rather than leaving minor overlap to inference.