Conciseness

The body is short but internally redundant and restates facts Claude already knows: the '50% smaller/better than JPEG' compression statistic appears three times (intro paragraph, Quick Reference bullet, and the Explain section), and the Check section repeats 'even better compression than WebP'. Fits anchor 3 ('mostly efficient but includes some unnecessary explanation or could be tightened') — not score 4 because the Quick Reference and Check/Explain sections are largely filler duplicating the intro; not score 2 because the overall length is still lean with no concept tutorials.

Actionability

There is some concrete guidance — 'Use picture element with WebP and JPEG fallbacks', the browser support list, and the Code Review section's instruction to 'Flag exact files or components where format choice, sizing, or loading behavior violates the rule' — but no executable code, command (e.g., avifenc/cwebp), DevTools procedure, or markup in the body; the actionable code lives entirely in references/rule.md. Matches anchor 3 (some concrete guidance, missing key details); below score 4 because 'Implement AVIF support with proper fallbacks' is a high-level instruction without the specific steps, above score 2 because the picture-element fallback mechanism is named concretely.

Workflow Clarity

A rough sequence exists (Check → Fix → Explain → Code Review), but checkpoints are absent: 'Check if the website supports AVIF format' gives no method (no DevTools Network-panel procedure, no markup inspection step), and there is no validation step to confirm the fallback works. Fits anchor 3 ('steps listed but validation gaps; checkpoints missing or implicit'); not score 4+ because the check/verify method is never specified, though the single-topic structure keeps it above score 2.

Progressive Disclosure

The body is a concise overview (~30 lines) and the details are cleanly split into one clearly signaled, one-level-deep reference: 'For full implementation details, code examples, and framework-specific guidance, see references/rule.md' — and references/rule.md is a real 211-line file containing the picture-element code example. This matches the score 5 anchor (clear overview with well-signaled one-level-deep references, content appropriately split, easy navigation); a lower score would require buried or nested references or inlined detail content, which is not the case.

Specificity

The description 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 together' — naming specific review dimensions. It stops short of score 5 because it never states what the skill produces or does beyond reviewing/checking (e.g., flagging, fixing, reporting), and the templated tail 'related to Use AVIF format for modern browsers' adds no concrete action; it is above score 3 because more than 1-2 specific actions with named scope are present.

Completeness

Both parts are present: an explicit 'Use when reviewing image assets, markup, and CDN or build transforms...' trigger clause, and a 'what' in 'Check encoded size, rendered size, loading strategy, and above-the-fold impact together'. Not score 5 because the 'when' clause is templated and awkward ('related to Use AVIF format for modern browsers') rather than a clean concrete trigger phrase, and the 'what' describes checking dimensions but not the underlying capability (AVIF adoption review/fallback implementation); it is above score 3 because both what and when are explicitly stated, not implied.

Trigger Term Quality

Natural terms users would say are present: 'AVIF', 'image assets', 'markup', 'CDN or build transforms', 'loading strategy'. Not score 5 because common variations and synonyms are missing — 'WebP', 'image format', 'fallbacks', 'picture element', 'image optimization' — and the awkward duplicated title phrase 'related to Use AVIF format for modern browsers' is not a natural user utterance; it is above score 3 because the key terms (AVIF, image assets, CDN/build transforms) are ones a user would plausibly say verbatim.

Distinctiveness Conflict Risk

The AVIF-specific focus ('Use AVIF format for modern browsers', 'image assets', 'CDN or build transforms') creates a clear niche with minimal conflict risk against unrelated skills. Not score 5 because the general framing 'reviewing image assets, markup, and loading strategy' could also overlap with closely related image skills such as responsive-images, lazy-loading, or WebP-format skills; it is well above score 3 since the AVIF anchor term makes mis-triggering unlikely.