Conciseness

The body contains no explanations of concepts Claude already knows; every sentence carries EmDash-specific contracts such as "Sandboxed runtime code can use Web APIs but not Node.js built-ins" and "decoded request/response bodies limited to 8 MiB". It is lean throughout and assumes competence, matching the score-5 anchor; there is no padding to trim as the score-4 anchor would require.

Actionability

The scaffold block ("pnpm dlx @emdash-cms/plugin-cli init my-plugin") and the complete, runnable `src/plugin.ts` example are copy-paste ready, and specific API names (`ctx.settings`, `ctx.kv`, `createPluginTestHost()`, `host.http.respond()`) cover the common cases, matching the score-5 anchor.

Workflow Clarity

Sections imply a clear sequence — choose format, scaffold, declare access, build routes/hooks/UI, then "Test the production boundary" with two concrete test-host factories and "Dispose every host after use". It falls short of the score-5 anchor because there is no explicit validate-fix-retry feedback loop (e.g., what to do when `pnpm run test` fails), but checkpoints are more present than absent, so it is above a 3.

Progressive Disclosure

The SKILL.md is a genuine overview: each section points to its one-level-deep reference ("Read [Hooks](./references/hooks.md)", "[Block Kit](./references/block-kit.md)"), all 12 referenced files exist in ./references/, and a consolidated References list aids navigation — a direct match for the score-5 anchor.

Specificity

The description enumerates the full concrete capability surface — "sandboxed hooks, routes, storage, content and media APIs, MCP tools, and declarative admin UI, or native React and Astro extensions" — giving comprehensive, specific coverage of what building a plugin involves rather than generic language.

Completeness

It explicitly answers both questions: the "what" is creating plugins with the enumerated subsystems, and the "when" is the concrete trigger clause "Use when scaffolding or implementing an EmDash plugin". Both are explicit with concrete trigger phrases, matching the score-5 anchor exactly; score 4 would require the 'when' to be less specific, which it is not.

Trigger Term Quality

Natural terms are present ("EmDash CMS plugins", "scaffolding or implementing an EmDash plugin", "MCP tools", "admin UI"), but common user variations like "build/develop a plugin" or "EmDash extension" are not covered; coverage is good with a few natural synonyms missing, matching the score-4 anchor rather than the comprehensive synonyms-and-extensions anchor at 5.

Distinctiveness Conflict Risk

"EmDash CMS" names a specific product niche with distinct triggers ("EmDash plugin", "sandboxed hooks", "MCP tools"); no other generic skill would plausibly match this description, so conflict risk is minimal.