Conciseness

The body is mostly efficient — compact per-platform summaries, a tight decision framework, and a reference table rather than inlined platform docs — but the eight 'Key Principles' entries restate HIG basics Claude already knows (e.g. 'macOS: pointer and keyboard. Dense information display... menu bars, toolbars'), and the trailing sections are padding: the 'When to Use' section ('This skill is applicable to execute the workflow or actions described in the overview') is vacuous filler, and the attribution footer adds tokens without guidance. This fits 'mostly efficient but includes some unnecessary explanation or could be tightened' rather than the minor-trim level 4.

Actionability

As an instruction-only skill, the guidance is concrete: an explicit context-check step ('Check for .claude/apple-design-context.md before asking questions'), five named discovery questions, a decision framework with concrete translation examples ('A macOS sidebar becomes a tab bar on iPhone'), and a specified output format (recommendations citing HIG sections, a platform differences table, implementation notes with recommended APIs). It stops short of level 5 because no worked example of the expected output (e.g. a sample differences table or citation format) is provided, leaving minor gaps in what 'citing relevant HIG sections' should look like.

Workflow Clarity

A coherent sequence is present: check existing context first, ask the five listed discovery questions, apply the five-step decision framework, then produce output in the three-part specified format. The reference index maps each platform to the file to consult per step. No validation checkpoints exist, but the skill is advisory (no destructive or batch operations), so the level-3 cap does not apply; it is not a 5 because there is no explicit feedback loop (e.g. re-checking recommendations against the framework or verifying cited HIG sections).

Progressive Disclosure

The body is a genuine overview: all seven per-platform guides live one level deep in references/ (all files verified to exist), and the Reference Index table clearly signals each file with its topic and key content ('designing-for-watchos.md | watchOS | Glanceable UI, Digital Crown, complications...'). Content is appropriately split and navigation is easy, matching the level-5 anchor exactly.

Specificity

The description 'Apple Human Interface Guidelines for platform-specific design' names the domain (Apple HIG, platform-specific design) but states no concrete actions — it is a topic phrase rather than a list of capabilities. It is above the level-1 'pure abstract language' anchor because the domain is clearly identified, but it matches 'names the domain but actions are minimal or generic' with no verbs or tasks at all.

Completeness

The 'what' is conveyed reasonably clearly (Apple HIG guidance applied to platform-specific design), but the 'when' is completely missing — there is no 'Use when...' clause or equivalent trigger guidance, which caps completeness at 3 per the judging guidelines. It is not a 2 because the what is more than vague; it is not a 4 because no when-clause exists at all.

Trigger Term Quality

'Apple' and 'Human Interface Guidelines' (HIG) are natural terms a user would say, but the most common trigger phrases for this skill — the platform names themselves (iOS, iPadOS, macOS, tvOS, visionOS, watchOS, SwiftUI, UI design) — are entirely absent. This fits 'some relevant keywords but missing common variations or synonyms'.

Distinctiveness Conflict Risk

'Apple Human Interface Guidelines for platform-specific design' carves out a clear niche and would not trigger for unrelated skills, and the Apple/HIG terms are distinctive. However, the skill body lists four closely related sibling skills (hig-foundations, hig-patterns, hig-components-layout, hig-components-content) whose descriptions could plausibly overlap, matching 'mostly distinct; minor overlap risk with closely related skills'.