Conciseness

The body is dense guidance with zero padding: it never explains what D3 is or how libraries work, and bullets like ".tickSizeOuter(0), 6-8 px tick padding" assume competence. The main trim opportunity is repetition — mobile/responsive guidance appears in Working Pattern (step 10), Editorial Defaults (two bullets), Integration Rules, and Output Expectations, which could be consolidated into one section.

Actionability

Guidance is unusually concrete for an instruction-only skill: exact pixel budgets ("10-12 px axis ticks, 1.5-2.25 px normal data lines"), specific API calls (".tickSizeOuter(0)", "d3-brush, d3-zoom, d3-drag"), and explicit CSS properties ("shape-rendering: crispEdges", "vector-effect: non-scaling-stroke") with when-to-use/when-not-to-use boundaries. It falls short of 5 only because there are no executable code snippets for a code-generation skill, e.g., a minimal data-join or scale-setup example.

Workflow Clarity

The 10-step "Working Pattern" gives a clear build sequence (data model -> separation of parsing/scales/geometry/rendering/interaction -> joins -> polish), and step 9 acts as a finishing checkpoint ("apply ./references/svg-polish-and-crispness.md before calling the chart finished"). Chart building is not a destructive or batch operation, so no validation cap applies, but there are no explicit validate/fix/retry feedback loops (e.g., checking rendered output against the data) that would earn a 5.

Progressive Disclosure

The SKILL.md is a genuine overview: detail is pushed into a clearly labeled References section split into "Shared theory" and "Skill references", and all five local ./references/ files exist and are one level deep with descriptive names. The gap is that 7 of the listed paths (../../references/foundations/*.md and two sibling SKILL.md files) are outside this bundle and not verifiable from it, slightly weakening navigation certainty relative to the 5 anchor.

Specificity

"Build custom data visualizations with D3" names the domain, and the description enumerates several concrete capability areas ("SVG or DOM-based charts", "rich annotation", "data joins", "custom scales or interactions", "scroll-driven SVG scene states"). It is one primary verb plus a scope list rather than multiple distinct actions (extract/fill/merge style), so it sits at 4 rather than 5.

Completeness

Both halves are explicit: the "what" is "Build custom data visualizations with D3" and the "when" is a concrete "Use when the user needs..." clause listing specific trigger conditions (charts, annotation, backgrounds, data joins, scales/interactions, scene states). This matches the anchor for clearly and explicitly answering both what and when with concrete trigger phrases; the 'when' is specific, not weakly implied, so 4 does not fit.

Trigger Term Quality

Natural terms users would say are well covered: "data visualizations", "D3", "charts", "SVG", "annotation", "interactions". Common variations like "graph", "plot", "visualize data", or chart-type words (scatterplot, bar chart) are missing, keeping it just below comprehensive.

Distinctiveness Conflict Risk

"custom data visualizations with D3" carves a clear niche with a named library and SVG/DOM framing, but trigger phrases like "rich annotation" and "scroll-driven SVG scene states" could also fire for closely related visualization skills (e.g., the scrollytelling skill referenced in the body). Mostly distinct with minor overlap risk, matching the 4 anchor.