typescript-strict

name	typescript-strict
description	Strict TypeScript patterns for safe, maintainable code. Use when writing or reviewing TypeScript, including .ts or .tsx files, schema validation, dependency injection, public API types, async control flow, and type-safety fixes.

TypeScript Strict

Use this skill to keep TypeScript strict, explicit, and runtime-safe without weakening the type system.

Core Rules

• Keep strict mode intact. Never weaken tsconfig to make errors disappear.
• Do not use any. Use unknown with narrowing when the type is genuinely unknown.
• Avoid as assertions. Use satisfies, discriminated unions, type guards, schemas, or better generic constraints.
• Avoid non-null assertions. Handle null and undefined explicitly.
• Prefer type for data shapes. Use interface for behavior contracts that implementations satisfy.
• Public functions and module boundaries should have explicit return types.
• Model domain state with discriminated unions and exhaustive switches.
• Use schema validation at runtime boundaries such as HTTP input, storage, config, and third-party data.

Workflow

1. Inspect local TypeScript conventions before editing.
2. Identify the runtime boundary and source of truth for each type.
3. Reuse existing schemas, validators, branded IDs, and domain types.
4. Fix the type shape at the source instead of silencing downstream errors.
5. Run the repo's typecheck, lint, and focused tests when available.

Detailed Reference

Read references/claude-typescript-strict.md when work involves schema organization, dependency injection, type-vs-interface decisions, or when the concise rules above are not enough.