SKILL.md
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- Building TypeScript/JavaScript libraries for npm
- Generating TypeScript declaration files (.d.ts)
- Bundling for multiple formats (ESM, CJS, IIFE, UMD)
- Optimizing bundles with tree shaking and minification
- Migrating from tsup with minimal changes
- Building React, Vue, Solid, or Svelte component libraries
Quick Start
# Install
pnpm add -D tsdown
# Basic usage
npx tsdown
# With config file
npx tsdown --config tsdown.config.ts
# Watch mode
npx tsdown --watch
# Migrate from tsup
npx tsdown-migrateBasic Configuration
import { defineConfig } from 'tsdown'
export default defineConfig({
entry: ['./src/index.ts'],
format: ['esm', 'cjs'],
dts: true,
clean: true,
})Core References
Topic
Description
Reference
Getting Started
Installation, first bundle, CLI basics
Configuration File
Config file formats, multiple configs, workspace
CLI Reference
All CLI commands and options
Migrate from tsup
Migration guide and compatibility notes
Plugins
Rolldown, Rollup, Unplugin support
For comprehensive migration assistance with complete option mappings, install the dedicated tsdown-migrate skill: npx skills add rolldown/tsdown --skill tsdown-migrate
| Hooks | Lifecycle hooks for custom logic | advanced-hooks |
| Programmatic API | Build from Node.js scripts | advanced-programmatic |
| Rolldown Options | Pass options directly to Rolldown | advanced-rolldown-options |
| CI Environment | CI detection, 'ci-only' / 'local-only' values | advanced-ci |
Build Options
Option
Usage
Reference
Entry points
entry: ['src/*.ts', '!**/*.test.ts']
Output formats
format: ['esm', 'cjs', 'iife', 'umd']
Output directory
outDir: 'dist', outExtensions
Type declarations
dts: true, dts: { sourcemap, compilerOptions, vue }
Target environment
target: 'es2020', target: 'esnext'
Platform
platform: 'node', platform: 'browser'
Tree shaking
treeshake: true, custom options
Minification
minify: true, minify: 'dce-only'
Source maps
sourcemap: true, 'inline', 'hidden'
Watch mode
watch: true, watch options
Cleaning
clean: true, clean patterns
Log level
logLevel: 'silent', failOnWarn: false
Dependency Handling
Feature
Usage
Reference
Never bundle
deps: { neverBundle: ['react', /^@myorg\//] }
Always bundle
deps: { alwaysBundle: ['dep-to-bundle'] }
Only bundle
deps: { onlyBundle: ['cac', 'bumpp'] } - Whitelist
Skip node_modules
deps: { skipNodeModulesBundle: true }
Auto external
Automatic dependency/peer/optional externalization
Output Enhancement
Feature
Usage
Reference
Shims
shims: true - Add ESM/CJS compatibility
CJS default
cjsDefault: true (default) / false
Package exports
exports: true - Auto-generate exports field
CSS handling
[experimental] css: { ... } — full pipeline with preprocessors, Lightning CSS, PostCSS, CSS modules, code splitting; requires @tsdown/css
CSS modules
css: { modules: { localsConvention: 'camelCase' } } — scoped class names for .module.css files
CSS inject
css: { inject: true } — preserve CSS imports in JS output
Unbundle mode
unbundle: true - Preserve directory structure
Root directory
root: 'src' - Control output directory mapping
Executable
[experimental] exe: true - Bundle as standalone executable, cross-platform via @tsdown/exe
Package validation
publint: true, attw: true - Validate package
Framework & Runtime Support
Framework
Guide
Reference
React
JSX transform, React Compiler
Vue
SFC support, JSX
Solid
SolidJS JSX transform
Svelte
Svelte component libraries (source distribution recommended)
WASM
WebAssembly modules via rolldown-plugin-wasm
Common Patterns
Basic Library Bundle
export default defineConfig({
entry: ['src/index.ts'],
format: ['esm', 'cjs'],
dts: true,
clean: true,
})Multiple Entry Points
export default defineConfig({
entry: {
index: 'src/index.ts',
utils: 'src/utils.ts',
cli: 'src/cli.ts',
},
format: ['esm', 'cjs'],
dts: true,
})Browser Library (IIFE/UMD)
export default defineConfig({
entry: ['src/index.ts'],
format: ['iife'],
globalName: 'MyLib',
platform: 'browser',
minify: true,
})React Component Library
export default defineConfig({
entry: ['src/index.tsx'],
format: ['esm', 'cjs'],
dts: true,
deps: {
neverBundle: ['react', 'react-dom'],
},
inputOptions: {
jsx: { runtime: 'automatic' },
},
})Preserve Directory Structure
export default defineConfig({
entry: ['src/**/*.ts', '!**/*.test.ts'],
unbundle: true, // Preserve file structure
format: ['esm'],
dts: true,
})CI-Aware Configuration
export default defineConfig({
entry: ['src/index.ts'],
format: ['esm', 'cjs'],
dts: true,
failOnWarn: 'ci-only', // opt-in: fail on warnings in CI
publint: 'ci-only',
attw: 'ci-only',
})WASM Support
import { wasm } from 'rolldown-plugin-wasm'
import { defineConfig } from 'tsdown'
export default defineConfig({
entry: ['src/index.ts'],
plugins: [wasm()],
})Library with CSS and Sass
export default defineConfig({
entry: ['src/index.ts'],
format: ['esm', 'cjs'],
dts: true,
target: 'chrome100',
css: {
preprocessorOptions: {
scss: {
additionalData: `@use "src/styles/variables" as *;`,
},
},
},
})Standalone Executable
export default defineConfig({
entry: ['src/cli.ts'],
exe: true,
})Cross-Platform Executable (requires @tsdown/exe )
export default defineConfig({
entry: ['src/cli.ts'],
exe: {
targets: [
{ platform: 'linux', arch: 'x64', nodeVersion: '25.7.0' },
{ platform: 'darwin', arch: 'arm64', nodeVersion: '25.7.0' },
{ platform: 'win', arch: 'x64', nodeVersion: '25.7.0' },
],
},
})Advanced with Hooks
export default defineConfig({
entry: ['src/index.ts'],
format: ['esm', 'cjs'],
dts: true,
hooks: {
'build:before': async (context) => {
console.log('Building...')
},
'build:done': async (context) => {
console.log('Build complete!')
},
},
})Configuration Features
Multiple Configs
Export an array for multiple build configurations:
export default defineConfig([
{
entry: ['src/index.ts'],
format: ['esm', 'cjs'],
dts: true,
},
{
entry: ['src/cli.ts'],
format: ['esm'],
platform: 'node',
},
])Conditional Config
Use functions for dynamic configuration:
export default defineConfig((options) => {
const isDev = options.watch
return {
entry: ['src/index.ts'],
format: ['esm', 'cjs'],
minify: !isDev,
sourcemap: isDev,
}
})Workspace/Monorepo
Use glob patterns to build multiple packages:
export default defineConfig({
workspace: 'packages/*',
entry: ['src/index.ts'],
format: ['esm', 'cjs'],
dts: true,
})CLI Quick Reference
# Basic commands
tsdown # Build once
tsdown --watch # Watch mode
tsdown --config custom.ts # Custom config
npx tsdown-migrate # Migrate from tsup
# Output options
tsdown --format esm,cjs # Multiple formats
tsdown -d lib # Custom output directory (--out-dir)
tsdown --minify # Enable minification
tsdown --dts # Generate declarations
tsdown --exe # Bundle as standalone executable
tsdown --unbundle # Bundleless mode
# Entry options
tsdown src/index.ts # Single entry
tsdown src/*.ts # Glob patterns
tsdown src/a.ts src/b.ts # Multiple entries
# Workspace / Monorepo
tsdown -W # Enable workspace mode
tsdown -W -F my-package # Filter specific package
tsdown --filter /^pkg-/ # Filter by regex
# Development
tsdown --watch # Watch mode
tsdown --sourcemap # Generate source maps
tsdown --clean # Clean output directory
tsdown --from-vite # Reuse Vite config
tsdown --tsconfig tsconfig.build.json # Custom tsconfigBest Practices
-
Always generate type declarations for TypeScript libraries:
{ dts: true }-
Externalize dependencies to avoid bundling unnecessary code:
{ deps: { neverBundle: [/^react/, /^@myorg\//] } }-
Use tree shaking for optimal bundle size:
{ treeshake: true }-
Enable minification for production builds:
{ minify: true }-
Add shims for better ESM/CJS compatibility:
{ shims: true } // Adds __dirname, __filename, etc.-
Auto-generate package.json exports:
{ exports: true } // Creates proper exports field-
Use watch mode during development:
tsdown --watch-
Preserve structure for utilities with many files:
{ unbundle: true } // Keep directory structure-
Validate packages in CI before publishing:
{ publint: 'ci-only', attw: 'ci-only' }Resources
- Documentation: https://tsdown.dev
- Rolldown: https://rolldown.rs
- Migration Guide: https://tsdown.dev/guide/migrate-from-tsup