Conciseness

The body is dense with genuinely non-obvious specifics (damping/response values, the exponential-decay projection, the rubber-band formula), but at ~290 lines it includes discursive material — the eight design principles in §16 and the process notes in §17 — that restates ideas Claude partly knows and could be tightened. This matches 'mostly efficient but could be tightened' rather than 4, which would require only minor trims.

Actionability

Highly concrete: exact spring parameter tables, executable CSS/JS for springs, projection, rubber-banding, and reduced-motion media queries. Below 5 because a few snippets are fragments (the pointerdown handler trails off with '// ...track position history' and §6 calls an undefined `animateSpringTo` helper), leaving minor gaps in copy-paste readiness.

Workflow Clarity

This is a knowledge/reference skill, not a multi-step process, so validation checkpoints aren't applicable; the numbered sections and the closing Quick Reference table make lookup unambiguous and the 'Initial Response' instruction is explicit. Not 5 because no explicit guidance sequences how to apply the principles when building or reviewing an interface (e.g. a review checklist order).

Progressive Disclosure

No bundle files exist and all ~290 lines live in SKILL.md. Sections are well-organized with clear headers, but substantial reference material — typography (§15) and the eight design principles (§16) — is inlined where it 'should be separate' per the anchor-3 description, and a Quick Reference table partially duplicates earlier sections. Not 2 because structure and navigation are good, not merely minimal.

Specificity

The description names many concrete capability areas — 'gesture-driven UI, spring animations, drag/swipe/sheet interactions, momentum and interruptible transitions, translucent materials and depth, typography (optical sizing, tracking, leading), reduced-motion' — matching the 'several specific actions; minor gaps' anchor. It stays below 5 because the framing is topical coverage rather than a list of discrete actions, and above 3 because coverage is broad rather than 1–2 items.

Completeness

It explicitly answers both questions: the 'what' ('Apple's approach to interface design and fluid, physical motion, translated for the web') and an explicit 'Use when building or reviewing…' clause with concrete trigger phrases, matching the top anchor. Not 4 because the 'when' is already fully explicit and specific, not merely present.

Trigger Term Quality

Natural phrases a user would actually say are well covered: 'spring animations', 'drag/swipe', 'reduced-motion', 'Apple-style interfaces'. It falls short of the 'comprehensive coverage including synonyms' anchor because common variations like 'framer motion', 'haptics', 'iOS-like feel', or library names users might mention are absent.

Distinctiveness Conflict Risk

It carves out a clear niche — Apple-derived fluid-motion and design guidance translated to web tech — with triggers unlikely to fire for unrelated skills. Minor theoretical overlap with a generic web-design skill exists, but the anchor-5 example's risk profile is equivalent.