Conciseness

The body is efficient — numbered Check/Fix steps carry concrete thresholds ("< 200KB for photos, < 50KB for graphics", "> 100px wide", "400w, 800w, 1200w, 1600w variants") with no explanations of concepts Claude doesn't know. Minor trim opportunities remain: the Quick Reference bullets duplicate Check/Fix items, and the opening motivation sentence is repeated verbatim in references/rule.md, so anchor 4 fits better than 5's 'every token earns its place'.

Actionability

Guidance is specific and executable in direction — exact size/quality thresholds, srcset variant widths, and per-issue fix steps — but the body contains no runnable commands or code: "Convert JPEG/PNG photos to WebP" lacks a conversion command, and the example markup lives only in references/rule.md. This matches anchor 4 ('mostly executable... minor gaps'); anchor 5 requires copy-paste-ready code or commands in the body itself.

Workflow Clarity

A clear phased sequence (Check → Fix → Explain) with the Check phase serving as per-image validation ("Report issues grouped by severity with file paths") and post-fix verification guidance ("describe how to confirm the fix in DevTools"). The gap is that there is no explicit re-run/re-check loop after applying fixes, so anchor 4 fits rather than 5; the batch scan does include verification steps, so the batch-operation cap of 3 does not apply.

Progressive Disclosure

A lean ~45-line overview body with a single, clearly signaled, one-level-deep reference: "For full implementation details, code examples, and framework-specific guidance, see `references/rule.md`" — verified to exist and to contain the deferred code examples and format comparison table. This matches anchor 5's clear overview with well-signaled one-level-deep references and easy navigation.

Specificity

Concrete actions quoted: "reviewing image assets, markup, and CDN or build transforms" and "Check encoded size, rendered size, loading strategy, and above-the-fold impact together". These list several specific actions with specific objects, but coverage has minor gaps — the skill's fix/explain capabilities are absent and the action verbs effectively reduce to review/check, matching anchor 4 rather than 5's comprehensive multi-verb coverage.

Completeness

Explicitly answers both parts: what — "Check encoded size, rendered size, loading strategy, and above-the-fold impact together"; when — "Use when reviewing image assets, markup, and CDN or build transforms". Both are concrete and explicit, matching anchor 5; anchor 4's example has a vaguer 'when' ("Use when working with PDF files") than this specific trigger phrasing.

Trigger Term Quality

Natural keywords present: "image assets", "markup", "CDN or build transforms", "loading strategy", "above-the-fold". However, common phrases a user would naturally say are missing — "image optimization", "WebP", "AVIF", "srcset", "lazy loading", "compress images" — which fits anchor 4 (good coverage, a few natural terms missing) rather than anchor 5's comprehensive synonym and extension coverage.

Distinctiveness Conflict Risk

Clear niche — web image optimization review — with distinct triggers ("image assets, markup, and CDN or build transforms") that would not fire for unrelated skills. It matches anchor 5's "clear niche with distinct triggers; minimal conflict risk"; it is not anchor 4 because overlap with generic web-performance skills is marginal given the image-specific scope.