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name: ts-library description: Use when authoring TypeScript libraries - covers project setup, package exports, build tooling (tsdown/unbuild), API design patterns, type inference tricks, testing, and release workflows. Patterns extracted from 20+ high-quality ecosystem libraries. license: MIT

TypeScript Library Development

Patterns for authoring high-quality TypeScript libraries, extracted from studying unocss, shiki, unplugin, vite, vitest, vueuse, zod, trpc, drizzle-orm, and more.

When to Use

• Starting a new TypeScript library (single or monorepo)
• Setting up package.json exports for dual CJS/ESM
• Configuring tsconfig for library development
• Choosing build tools (tsdown, unbuild)
• Designing type-safe APIs (builder, factory, plugin patterns)
• Writing advanced TypeScript types
• Setting up vitest for library testing
• Configuring release workflow and CI

For Nuxt module development: use nuxt-modules skill

Quick Reference

Key Principles

• ESM-first: "type": "module" with .mjs outputs
• Dual format: always support both CJS and ESM consumers
• moduleResolution: "Bundler" for modern TypeScript
• tsdown for most builds, unbuild for complex cases
• Smart defaults: detect environment, don't force config
• Tree-shakeable: lazy getters, proper sideEffects: false

Token efficiency: Main skill ~300 tokens, each reference ~800-1200 tokens