Conciseness

The body avoids explaining concepts Claude already knows (it defers mapped-type mechanics to a sibling skill) and its code examples are tight, but the triggers are restated three times — "When to Apply" (8 bullets), "Use When" (4 quotes), plus the description — and "Out of Scope" repeats verbatim in "When NOT to Use" (deep-readonly named twice). This is the 3 anchor ("mostly efficient but includes some unnecessary explanation or could be tightened") rather than 2, since nothing is conceptually padded — the redundancy is structural duplication that could be merged.

Actionability

The three anti-patterns give executable BAD/GOOD TypeScript pairs (e.g., `type UserUpdate = Partial<User>` vs a hand-written interface), and the References table maps each need to a concrete file, but the body itself gives no inline example of the two tasks users most need shown — key remapping and custom mapped types are only pointed at. This fits the 4 anchor ("mostly executable guidance; concrete code or commands with minor gaps") rather than 5, since the common cases rely on navigation rather than inline copy-paste coverage.

Workflow Clarity

The decision path is clear: Mindset establishes built-in-first, combine-don't-invent rules; When to Apply lists triggers; and the References table routes each need to its file, with `npx tsc --noEmit` offered as verification. It sits at the 4 anchor rather than 5 because the validation command is presented as a loose "Quick Commands" item rather than an integrated step (e.g., "apply the transform, then type-check"), leaving a minor checkpoint gap; no destructive/batch cap applies since this is a non-destructive selection skill.

Progressive Disclosure

The body is a genuine overview: mindset, triggers, scope boundaries, anti-patterns, and a References table routing to all 8 bundle files — each of which exists in `references/` exactly as listed, is one level deep, and is labeled with what it covers. This matches the 5 anchor (clear overview with well-signaled one-level-deep references, content appropriately split, easy navigation).

Specificity

The description enumerates concrete, specific content exhaustively — "Partial/Required, Pick/Omit, Readonly/Record, Extract/Exclude, NonNullable/Awaited, ReturnType/Parameters/ConstructorParameters/InstanceType, key remapping with `as` in mapped types, and hand-rolled custom mapped types" — covering the full built-in utility surface plus custom construction. This is comprehensive coverage of multiple specific concrete items, matching the 5 anchor rather than the 4 anchor ("several specific actions; minor gaps"), since no built-in utility family is omitted.

Completeness

Both questions are explicitly and concretely answered: what — "TypeScript's built-in utility types and how to build custom ones" with a full enumeration — and when — "Use when picking the right built-in utility type..., extracting a function's parameter or return type, filtering a union with Extract/Exclude, or remapping object keys". This matches the 5 anchor (clear what AND when with concrete trigger phrases), not the 4 anchor where "when" could be more explicit.

Trigger Term Quality

The "Use when" clause gives natural trigger phrasings — "picking the right built-in utility type instead of hand-writing one, extracting a function's parameter or return type, filtering a union with Extract/Exclude, or remapping object keys" — and the what-clause names the exact type names users would mention. It falls just short of the 5 anchor (comprehensive synonyms/extensions) because common user phrasings like "make all properties optional", "read-only", or "subset of a type" are absent, but it clearly exceeds the 3 anchor ("some relevant keywords, missing common variations") since the utility names themselves are the natural vocabulary.

Distinctiveness Conflict Risk

The niche is clear (TypeScript's ready-made utility types) with distinctive triggers around Extract/Exclude and ReturnType/Parameters, but the clause "key remapping with `as` in mapped types" overlaps with a sibling type-system skill's mapped-type territory — the description itself does not demarcate that boundary (the body does). This fits the 4 anchor ("mostly distinct; minor overlap risk with closely related skills") rather than 5 ("minimal conflict risk"), while clearly exceeding the 3 anchor's broader overlap.