typescript-typecheck — SKILL.md

Variant: standard · When to use: the skill is invoked, runs to completion, returns a configured type-check gate (tsconfig + scripts + CI step), control passes back to the caller.

Overview

TypeScript's compiler (tsc) is the only tool that actually checks types. Bundlers and transpilers in a typical TS toolchain — Vite (esbuild in dev, Rollup in prod) and the SWC-based React plugin — transpile/strip type annotations without checking them. That means vite build (or any esbuild/SWC build) compiles successfully even when the code is full of type errors. This skill sets up the missing piece: a dedicated tsc --noEmit type-check gate that runs locally and in CI, backed by a genuinely strict tsconfig, plus TypeScript project references so cross-package types resolve in a monorepo. It is the type-system analog of a separate static-analysis gate — a linter (Biome/ESLint) finds style and bug patterns but has no type system and cannot do this job. Pinned to TypeScript 5.x. Verified flag list and worked examples live in references/.

When to activate

• ✅ Setting up TypeScript type-checking for a project for the first time (a typecheck script + CI step).
• ✅ Writing or tightening a tsconfig.json and wanting it genuinely strict (not just strict: true).
• ✅ Configuring moduleResolution: "bundler" for a Vite/esbuild/bundler app and getting the companion flags right.
• ✅ Setting up TypeScript project references (composite, references, tsc -b) so an app package can consume a library/generated package's types in a monorepo.
• ✅ Adding a CI type-check gate (e.g. GitHub Actions with pnpm) that fails the build on a type error the bundler would have ignored.

Do NOT activate when: