TypeScript stack

Preserve valid project and framework conventions. Apply this skill to the language layer; let framework skills own routing, rendering, deployment, and framework-required file shapes, and let project-structure own language-neutral repository policy.

Compiler and runtime

• Verify the current stable TypeScript version and runtime compatibility from

primary sources before adding or upgrading the compiler. Pin the selected version in the project lockfile.

• Start from the runtime or framework's maintained tsconfig base when one

exists. Otherwise enable strict, noUncheckedIndexedAccess, exactOptionalPropertyTypes, noImplicitOverride, and useUnknownInCatchVariables.

• Align target, lib, module format, module resolution, emitted extensions,

and ambient types with the actual runtime and deployment target. Do not make bundler, Node, Bun, or browser assumptions that the project does not satisfy.

• Use noEmit when another tool owns output. When TypeScript emits production

code, validate the emitted artifact on the target runtime as well as running the typecheck.

Types and APIs

• Do not use any. Accept unknown at untrusted boundaries, validate or narrow

it once, and keep the validated type downstream.

• Prefer inference inside an implementation and explicit types at public,

serialized, asynchronous, and dependency boundaries.

• Model variant state with discriminated unions and exhaustively handle it.

Avoid boolean combinations that admit invalid states.

• Use full, domain-specific names. Avoid catch-all utils, helpers, or lib

modules.

• Avoid non-null assertions and type assertions. When an external invariant

requires one, keep it at the boundary and explain the invariant locally.

• Use @ts-expect-error only for an intentional, described type-level test.

Never use @ts-ignore to make the project gate pass.

Modules and validation

• Follow the runtime, framework, and project's established module boundaries and

public API layout. Keep dependency direction visible and avoid cycles.

• Test observable runtime behavior and type contracts that can regress. Keep

compile-time fixtures separate from runtime assertions.

• Run focused tests, the repository gate, and TypeScript with no emit. If the

compiler owns production emission, validate the emitted output on its target runtime instead.