Conciseness

The ~58-line body is pure imperative guidance with zero conceptual padding — nothing explains what the APIs or JavaScript are; every line carries skill-specific nuance (e.g., "Treat `availability()` as a capability check, not a guarantee that creation will succeed without user interaction or download time"). The only trimmable redundancy is the worker/server rule appearing in both Step 2 and Error Handling, which is too minor to fall from the anchor-5 'every token earns its place' to anchor 4.

Actionability

Guidance is fully executable: a concrete command ("Execute `node scripts/find-writing-assistance-targets.mjs .`"), exact API surfaces (`availability()`, `create()` with `monitor`, `AbortController`, `destroy()`, `sharedContext` vs per-call `context`), named exceptions (`NotAllowedError`, `NotSupportedError`, `QuotaExceededError`) each with remediation, and a code template asset. Per the rubric's scoring notes, an instruction-only skill is not penalized for absent inline code when the guidance is this concrete.

Workflow Clarity

Five clearly sequenced steps with an explicit validation phase: Step 5 re-runs the inventory script to confirm the integration surface, verifies feature detection and availability before deeper debugging, requires testing batch and streaming modes, confirms cancellation and destroy semantics, and runs the workspace build/typecheck/tests. The Error Handling section supplies validate-then-fix feedback loops, matching the score-5 anchor; checkpoints are explicit, so it is not the score-4 anchor.

Progressive Disclosure

The body is a lean overview delegating detail to four one-level-deep reference files, each with a crisp conditional signal ("Read `references/examples.md` when the feature needs a session shape for monitoring downloads, batch output, streaming output, or cancellation"), plus a script and a template asset — all verified to exist on disk with no nested reference chains. This matches the score-5 anchor of well-signaled, appropriately split, easy-to-navigate content.

Specificity

The description names the domain ("browser Summarizer, Writer, and Rewriter integrations") and lists many concrete actions — "availability checks, model download UX, session creation, summarize or write or rewrite flows, streaming output, abort handling, or permissions-policy constraints" — giving comprehensive, not merely several, concrete actions; that matches the score-5 anchor rather than the score-4 anchor's 'minor gaps in coverage'.

Completeness

It explicitly answers both 'what' ("Implements and debugs browser Summarizer, Writer, and Rewriter integrations in JavaScript or TypeScript web apps") and 'when' ("Use when adding availability checks, model download UX, session creation, summarize or write or rewrite flows, streaming output, abort handling, or permissions-policy constraints") with concrete trigger phrases — the exact structure of the score-5 anchor example; it is not the score-4 anchor since 'when' is fully explicit rather than improvable.

Trigger Term Quality

Natural trigger phrasings a user would actually say are present: "Summarizer, Writer, Rewriter", "summarize or write or rewrite", "streaming output", "model download", "session creation", plus framework variants ("JavaScript or TypeScript web apps") and synonyms per surface. Coverage is comprehensive including synonyms, matching the score-5 anchor; the score-4 anchor ('a few natural terms missing') understates it.

Distinctiveness Conflict Risk

It occupies a clear niche (built-in browser writing-assistance APIs) and adds an explicit negative trigger — "Don't use for generic prompt engineering, server-side LLM SDKs, or cloud AI services" — which resolves overlap with adjacent LLM skills. Minimal conflict risk matches the score-5 anchor.