Conciseness

The body is lean and dense — two tables, one code block, and a rules paragraph with zero conceptual padding or explanations of things Claude already knows. The repeated Mediator-not-MediatR warning at the top is the one deliberate emphasis of the skill's #1 failure mode, and it earns its tokens; every other line is novel, project-specific information.

Actionability

Fully concrete guidance: exact interface names in a use/don't-use table, a copy-ready command+handler pattern with the real project folder paths, exact registration code for both Program.cs hosts, and a symptom→cause→fix error table. The {X}/{Entity} placeholders are template parameters of the module procedure rather than pseudocode, and the specific examples cover the common cases, matching the 5 anchor.

Workflow Clarity

The registration section lays out a clear, countable procedure ("two markers", "in both FSH.Starter.Api/Program.cs and FSH.Starter.DbMigrator/Program.cs") and the Common errors table provides symptom→fix recovery, but there is no explicit validation checkpoint (e.g. verify the handler resolves/compiles after registration) — clear sequence with a minor checkpoint gap, matching 4 rather than 5.

Progressive Disclosure

At ~60 lines the body is a well-organized single-level overview: everything needed at a glance (interfaces, pattern, registration, errors) lives inline, and the deeper multi-step procedure is cleanly delegated one level out via "See `add-module` for the full procedure." No nested references, no inlined content that belongs elsewhere; navigation is easy.

Specificity

The description names the domain ("CQRS interface reference for FSH") and several concrete items ("commands, queries, and handlers") plus a sharp library distinction ("Mediator source generator, NOT MediatR"), but it does not enumerate other capabilities the body covers such as handler registration or common error fixes — minor gaps in coverage, matching the 4 anchor rather than the comprehensive 5.

Completeness

It explicitly answers both questions: what ("CQRS interface reference for FSH... uses the Mediator source generator, NOT MediatR") and when ("Reference when implementing commands, queries, and handlers") with concrete trigger phrases — a direct match to the 5 anchor.

Trigger Term Quality

"CQRS", "commands, queries, and handlers", "Mediator", and "MediatR" are exactly the terms a user in this codebase would naturally say, giving good keyword coverage. Not a 5 because a few natural trigger variations the body serves (e.g. "send a command", "handler not invoked", "AddMediator/registration") are absent.

Distinctiveness Conflict Risk

The niche is unmistakable: scoped to FSH, explicitly disambiguated against MediatR, so it will not fire for generic CQRS or MediatR questions. Clear distinct triggers, minimal conflict risk.