Conciseness

The body is lean and fully operational — no basic-concept explanations, and every line is either instruction or curated engine-divergence knowledge Claude cannot reliably recall unprompted ("Firefox's overlay scrollbar vs WebKit/Chromium's reserved gutter can shift layout width", "don't assume multi-browser config exists"). No section reads as padding, matching the 'every token earns its place' anchor.

Actionability

Concrete and mostly executable: a fixed viewport (992×900), a copy-paste command (`npx playwright test --project=chromium --project=firefox --project=webkit`), a capture naming convention (`<page-slug>-<engine>.png`), named risk features (`:has()`, container queries, `backdrop-filter`), and a worked findings example. Held at 4 rather than 5 because the primary Playwright-MCP capture path is described only in prose and there is no fallback command if an engine's browser binary is not installed.

Workflow Clarity

Phase 0–3 sequence is clear (Scope → Capture → Checklist → Findings) with an explicit side-by-side checklist and a severity-ranked output format including a good-vs-bad findings example. Missing an explicit checkpoint confirming all three engine captures succeeded and are viewport-comparable before diffing, and no recovery guidance for a failed engine launch, which keeps it below the 'explicit validation steps; feedback loops' anchor.

Progressive Disclosure

A single ~90-line SKILL.md with clean section headers and no bundle files; nothing at this size warrants splitting into reference files, and cross-skill routing pointers (`responsive-visual-review`, `playwright-testing`) are clearly signaled. This fits the well-organized single-file case the rubric treats as a 5.

Specificity

The description names concrete objects and contexts — "check browser-specific CSS/layout/JS rendering differences (Chromium/Firefox/WebKit)" plus two use contexts — which on content alone fits the 'several specific actions; minor gaps' anchor (4). However, "Use when you need to check" is second-person voice ("you need"), which the guidelines explicitly penalize by one point, bringing it to 3.

Completeness

Explicitly answers both parts: what ("check browser-specific CSS/layout/JS rendering differences (Chromium/Firefox/WebKit)") and when ("before shipping a CSS/JS change or investigating compatibility issues across engines") with concrete trigger phrases — a direct match for the anchor-5 example structure.

Trigger Term Quality

Good natural keyword coverage: "browser-specific", "rendering differences", "compatibility issues", "CSS/JS", and all three engine names. Not 5 because the phrases users most commonly say — "cross-browser" and "Safari" — never appear literally, leaving a few natural synonyms missing.

Distinctiveness Conflict Risk

Three explicit NOT-for clauses each route to a named alternative skill (responsive-visual-review, playwright-testing, polyfill design), establishing a clear niche with minimal conflict risk — stronger than the anchor-5 example, which has no such explicit disambiguation.