Individual skill
typescript-strict
Write and review TypeScript as if strict mode plus the hardening flags (noUncheckedIndexedAccess, exactOptionalPropertyTypes) are enforced, and migrate loose codebases to full strictness flag by flag without breaking the build. Use when someone asks "how do I get rid of any", "turn on strict mode in an existing project", "is this type assertion safe", "why does tsc say possibly undefined", or when writing new TypeScript that must pass a strict compiler. Do NOT use for migrating between language or runtime versions - use language-version-migrator instead.
skills/typescript-strict/SKILL.md
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# TypeScript Strict Mode
Every `any` is a runtime bug that the compiler was ready to catch and was told not to. Strict TypeScript converts a class of production failures - undefined access, wrong-shape API responses, unhandled union cases - into compile errors that cost seconds instead of incidents. This skill enforces strictness in new code and migrates existing loose codebases without a big-bang rewrite.
## Operating procedure
1. **Determine the mode.** Greenfield code: apply the full config and the banned/required patterns below from the first commit. Existing loose codebase: jump to the migration procedure - do not flip every flag at once, because a wall of 2,000 errors gets the whole effort reverted.
2. **Set the config.** The target tsconfig is the artifact below. `"strict": true` is the floor, not the ceiling - `noUncheckedIndexedAccess` and `exactOptionalPropertyTypes` catch real bugs that `strict` alone misses.
3. **Write to the banned/required pattern lists.** Every review comment and every fix should cite one of them.
4. **Prefer narrowing over asserting.** When the compiler complains, the question is "how do I prove this to the compiler," not "how do I silence it." Use the narrowing toolkit.
5. **Contain unavoidable casts with the escape-hatch policy.** A cast is a claim the compiler cannot check; isolate it, validate it, and never let it propagate.
## Inputs to collect
