Conciseness

The body is lean and every sentence carries project-specific, non-inferable facts ('There is no generic IRepository<T>. Inject the module's {X}DbContext', 'TreatWarningsAsErrors', 'Architecture.Tests fails the build if a command... has no validator'). It explains nothing Claude already knows, matching the anchor-5 profile of every token earning its place.

Actionability

Every step ships complete, executable C# (command record, handler with guard clause and SaveChangesAsync, validator with rules, endpoint with permission/idempotency wiring) plus exact shell commands ('dotnet build src/FSH.Starter.slnx', 'dotnet test src/Tests/{X}.Tests'). The {Entity}-style placeholders are the skill's argument interface rather than pseudocode, and the single ellipsis in Step 5 legitimately denotes pre-existing user code.

Workflow Clarity

Steps 1-6 are clearly numbered with an explicit verification step (build with 0 warnings, add a test) and a closing checklist, which goes beyond anchor 3's implicit checkpoints. It falls short of anchor 5 because there is no error-recovery feedback loop — e.g., what to do when Architecture.Tests fails the build or when warnings appear — leaving that recovery implicit.

Progressive Disclosure

The file is well-sectioned, self-contained for the core workflow, and defers bulk conventions to one-level-deep references signaled up front ('Full conventions: .agents/rules/api-conventions.md'). It sits below anchor 5 because two inline references ('see query-patterns', 'see testing-guide') are given as bare names without paths or links, making navigation to them slightly ambiguous.

Specificity

The description enumerates the concrete artifacts produced ('command/query + handler + validator + endpoint') within a named vertical-slice architecture, giving comprehensive and specific coverage of what the skill does. Anchor 4 would require minor gaps in coverage, but every artifact of the feature slice is listed.

Completeness

It explicitly answers both questions: what ('Add a vertical-slice feature (command/query + handler + validator + endpoint) to an existing FSH module') and when ('Use when adding an API endpoint or business operation to a module that already exists') with concrete trigger phrases, matching the anchor-5 pattern exactly.

Trigger Term Quality

Natural phrases users would say are present ('adding an API endpoint', 'business operation', 'add a vertical-slice feature'), giving good coverage. It misses common variations such as 'add CRUD', 'add a query', 'new endpoint', or 'add an operation', so it falls below the comprehensive-synonym coverage of anchor 5.

Distinctiveness Conflict Risk

The niche is sharply defined — FSH modules, existing-module scope, endpoint/business-operation triggers — which cleanly distinguishes it from sibling skills like creating a new module. It is written in third-person imperative form with no vague overlap language, so conflict risk is minimal.