Conciseness

The body is a ~25-line table of terse, one-line rules with zero padding and no explanation of concepts Claude already knows ('Apply the type-system-discipline principle skill first; this skill grounds it in TypeScript syntax' assumes full competence). Every token earns its place.

Actionability

The rules are concrete and executable: exact syntax ('Inline `const _exhaustive: never = x;` in default arms', 'Brand primitives with `& { readonly __brand: "X" }`'), naming conventions ('Name them `isX` or `hasX`'), and an ordered narrowing hierarchy, all backed by copy-paste-ready code in references/patterns.md covering every rule. Per the instruction-skill note, the absence of inline code blocks is not penalized since the guidance is specific and the referenced examples are complete.

Workflow Clarity

This is a simple single-purpose skill (under 50 lines, one task: apply these rules to TS code), and the single action is unambiguous, with an explicit sequencing step ('Apply the type-system-discipline principle skill first'). No destructive or batch operations exist that would require validation checkpoints, so the simple-skill exception applies.

Progressive Disclosure

SKILL.md is a concise overview (rule table) with the bulk code examples split into exactly one clearly-signaled reference ('Examples: `references/patterns.md`'), which exists, is one level deep, and contains no nested file references. The split is appropriate and navigation is trivial.

Specificity

The description only says 'TypeScript best practices' — it names the domain but lists no concrete actions (no mention of discriminated unions, type guards, boundary validation, etc.), matching the 'Names the domain but actions are minimal or generic' anchor. Not 3 because no 1-2 specific capabilities are stated; not 1 because the domain is clearly identified.

Completeness

Both parts are present: a 'what' ('TypeScript best practices') and an explicit 'when' ('Use when reading or editing any .ts or .tsx file'), so the missing-'Use when' cap does not apply. Not 5 because the 'what' is a bare category rather than concrete capability phrases; the 'when' is fully explicit, so it clears the 4 anchor.

Trigger Term Quality

Includes natural terms users would say — 'TypeScript', 'reading or editing', '.ts', '.tsx' — giving good keyword coverage. Not 5 because common variations like 'type safety', 'type errors', 'types', or 'narrowing' are missing; not 3 because both the language name and file extensions are present.

Distinctiveness Conflict Risk

'reading or editing any .ts or .tsx file' is somewhat specific but any other TypeScript-related skill (linting, tsconfig, refactoring) would trigger on the same condition, creating overlap risk with similar skills. Not 4 because the trigger is broader than 'minor overlap risk'; not 2 because the domain is clearly TypeScript, not generic.