Conciseness

The body is almost entirely lean, executable code with minimal prose and no explanations of concepts Claude already knows. It falls short of 5 only because of minor duplication: KeyPath-modifier ordering appears both in 'Vectorized Plots' and Common Mistake #7, and angle-selection-to-category mapping appears both in 'Selection' and Common Mistake #9. This fits the level-4 anchor (efficient, minor instances that could be trimmed) rather than 5 (every token earns its place).

Actionability

Copy-paste-ready Swift snippets cover every mark type, axis customization, scale configuration, encoding, selection, scrolling, annotations, legends, vectorized plots, and 3D charts, and Common Mistakes show explicit WRONG/CORRECT pairs. This matches the level-5 anchor of fully executable guidance covering common cases.

Workflow Clarity

The Workflow section sequences ten concrete steps with an explicit validation matrix (step 9: render empty, typical, dense, large-text, high-contrast, and VoiceOver states) and an error-recovery feedback loop (step 10: restore the fixture, fix one layer, rerun the same matrix), plus a separate review workflow and a Review Checklist. This matches the level-5 anchor (explicit validation, feedback loops, checklists).

Progressive Disclosure

SKILL.md serves as a well-organized overview with a Contents TOC, and the single bundle file references/charts-patterns.md (verified to exist, ~976 lines of extended patterns) is clearly signaled three times with a description of what it contains. References are exactly one level deep and the References section adds curated external links, matching the level-5 anchor.

Specificity

The description lists multiple concrete actions ('Implement, review, or improve data visualizations using Swift Charts') and comprehensively enumerates capabilities ('building bar, line, area, point, pie, donut, or iOS 26 3D charts; when adding chart selection, scrolling, annotations, axes, scales, legends') down to named APIs (BarPlot, LinePlot, Chart3D, SurfacePlot). This matches the level-5 anchor of multiple specific concrete actions with comprehensive coverage; no evident gaps place it at 4.

Completeness

Both 'what' ('Implement, review, or improve data visualizations using Swift Charts') and 'when' are explicitly and concretely answered with four 'Use when...' trigger clauses covering chart types, features, plot APIs, and specialized chart kinds. This mirrors the level-5 example structure exactly, well above the level-4 anchor where the 'when' is less specific.

Trigger Term Quality

Natural user phrases are covered comprehensively: chart type names users would actually say ('bar, line, area, point, pie, donut', 'heat maps, Gantt charts, grouped bars, sparklines, threshold lines') plus feature terms ('chart selection, scrolling, annotations, axes, scales, legends') and developer API names. Matches the level-5 anchor for comprehensive natural-term coverage; no meaningful terms are missing.

Distinctiveness Conflict Risk

The description is clearly scoped to Swift Charts on iOS with distinct triggers (named marks, plot APIs, iOS 26 3D charts), giving it a clear niche with minimal conflict risk against generic data-visualization or document skills. Matches the level-5 anchor.