Agent Skills: Strict TypeScript

Strict TypeScript

Critical rules

• strict: true is the floor. Also enable noUncheckedIndexedAccess, exactOptionalPropertyTypes, verbatimModuleSyntax, erasableSyntaxOnly, and related unused/fallthrough flags.
• Ban any / as / non-null assertions in source. Narrow with guards, discriminated unions, or Zod.
• Install @total-typescript/ts-reset so JSON.parse is unknown.
• Prefer satisfies and as const over loose object typing; avoid barrels and erasable-syntax violations (enum, param properties).
• Enforce with @typescript-eslint/strict-type-checked at 'error'.
• Before editing tsconfig or patterns, read references/tsconfig.md and references/type-patterns.md.

Workflow

1. Audit tsconfig.json against the required flags in references/tsconfig.md.
2. Add reset.d.ts importing @total-typescript/ts-reset.
3. Enable strict ESLint type-checked rules — see references/eslint-and-build.md.
4. Replace as/any with guards, unions, or Zod; brand confusable IDs.
5. Prefer direct imports over barrels; profile with tsc --extendedDiagnostics if compile is slow.
6. Confirm tsc --noEmit and ESLint pass clean.

Resources

• references/tsconfig.md — required flags and explanations. Read when configuring.
• references/type-patterns.md — narrowing, ts-reset, type-fest, branded types. Read when fixing unsafe code.
• references/eslint-and-build.md — ESLint, barrels, build tools, rationalizations. Read when enforcing in CI.

Validation

• [ ] Supplementary strict flags all enabled
• [ ] ts-reset installed via reset.d.ts
• [ ] No any/as in source (fixtures aside); narrowing is typed
• [ ] satisfies / as const for literal configs
• [ ] Strict type-checked ESLint rules are 'error'
• [ ] No hot-path barrel files; tsc --noEmit clean

Constraints

• Prototypes may trade safety for speed; runtime input parsing belongs in validation-boundary.
• Related: pattern-enforcement, validation-boundary, fn-args-deps, result-types.