Conciseness

The body is short and mostly efficient, but the 'Explain' section repeats the intro's sentence verbatim ('A <picture> without an <img> fallback renders nothing in browsers that don't support <picture> (IE11)...') and re-explains how <picture> source selection works — a concept Claude already knows. The 'Code Review' section also largely restates the description. Not a 4 because there are two genuinely redundant sections, not just minor trimming.

Actionability

The 'Check' section enumerates six concrete verifications (img as last child, alt, width/height, source ordering, srcset/media, type attributes) and 'Fix' gives exact remediation with concrete markup like 'add <img src="{fallback-url}" alt="{description}" width="{w}" height="{h}">' and 'type="image/avif"'. Not a 5 because the fix markup uses placeholders rather than a copy-paste-ready example, and no inline code snippet is shown (examples live only in the reference).

Workflow Clarity

Clear Check → Fix → Code Review sequence with enumerated steps ('Scan all <picture> elements... Verify: 1)–6)') and a verification checkpoint ('describe how to confirm the fix in DevTools'). Not a 5 because there is no explicit re-check loop after fixes are applied (fix → re-scan), leaving the batch-review workflow's feedback loop implicit.

Progressive Disclosure

The ~45-line body is well organized into Quick Reference / Check / Fix / Explain / Code Review sections and delegates full implementation detail via a single, clearly signaled one-level reference: 'see `references/rule.md`' — a file that exists in the bundle. No nested references and nothing inlined that belongs in a separate file.

Specificity

Lists several concrete actions — 'reviewing image assets, markup, and CDN or build transforms' and 'Check encoded size, rendered size, loading strategy, and above-the-fold impact' — which name concrete review targets and checks. Not a 5 because the embedded rule title 'related to Use <picture> with an <img> fallback' muddles the action list, and coverage of what the review entails is partially delegated to that phrase.

Completeness

Both parts are present: an explicit trigger clause ('Use when reviewing image assets, markup, and CDN or build transforms...') and a clear what ('Check encoded size, rendered size, loading strategy, and above-the-fold impact together'). Not a 5 because the 'what' is fragmented across two sentences and the awkward 'related to Use <picture> with an <img> fallback' construction makes the scope less explicit than the anchor's crisp statement.

Trigger Term Quality

Good natural keywords a frontend reviewer would say: 'image assets', 'markup', 'CDN or build transforms', 'loading strategy', 'above-the-fold'. Not a 5 because common variations and synonyms are missing — e.g. 'srcset', 'responsive images', 'WebP/AVIF', or file extensions.

Distinctiveness Conflict Risk

The <picture>/<img> fallback niche is distinct with targeted triggers (image markup, CDN transforms, loading strategy), so conflict risk with unrelated skills is low. Not a 5 because 'reviewing image assets' is broad enough to overlap with sibling image-optimization skills in the same category.