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tsdown

Fast TypeScript/JavaScript library bundler powered by Rolldown with multi-format output and type declaration generation. Supports bundling to ESM, CJS, IIFE, and UMD formats with automatic peer dependency externalization and tree shaking Generates TypeScript declaration files (.d.ts) with source map and compiler option control, plus experimental CSS pipeline with preprocessor and PostCSS support Includes watch mode, minification, source maps, unbundle mode for preserving directory structure, and framework-specific recipes for React, Vue, Solid, and Svelte Offers CLI commands, programmatic API, lifecycle hooks, workspace/monorepo support, and direct Rolldown option passthrough for advanced customization Provides migration tooling from tsup and experimental features for standalone executable bundling and package validation (publint, attw)

INSTALLATION
npx skills add https://github.com/antfu/skills --skill tsdown
Run in your project or agent environment. Adjust flags if your CLI version differs.

SKILL.md

tsdown - The Elegant Library Bundler

Blazing-fast bundler for TypeScript/JavaScript libraries powered by Rolldown and Oxc.

When to Use

  • 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-migrate

## Basic 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
[guide-getting-started](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/guide-getting-started.md)

Configuration File
Config file formats, multiple configs, workspace
[option-config-file](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-config-file.md)

CLI Reference
All CLI commands and options
[reference-cli](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/reference-cli.md)

Migrate from tsup
Migration guide and compatibility notes
[guide-migrate-from-tsup](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/guide-migrate-from-tsup.md)

Plugins
Rolldown, Rollup, Unplugin support
[advanced-plugins](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/advanced-plugins.md)

Hooks
Lifecycle hooks for custom logic
[advanced-hooks](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/advanced-hooks.md)

Programmatic API
Build from Node.js scripts
[advanced-programmatic](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/advanced-programmatic.md)

Rolldown Options
Pass options directly to Rolldown
[advanced-rolldown-options](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/advanced-rolldown-options.md)

CI Environment
CI detection, `'ci-only'` / `'local-only'` values
[advanced-ci](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/advanced-ci.md)

## Build Options

Option
Usage
Reference

Entry points
`entry: ['src/*.ts', '!**/*.test.ts']`
[option-entry](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-entry.md)

Output formats
`format: ['esm', 'cjs', 'iife', 'umd']`
[option-output-format](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-output-format.md)

Output directory
`outDir: 'dist'`, `outExtensions`
[option-output-directory](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-output-directory.md)

Type declarations
`dts: true`, `dts: { sourcemap, compilerOptions, vue }`
[option-dts](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-dts.md)

Target environment
`target: 'es2020'`, `target: 'esnext'`
[option-target](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-target.md)

Platform
`platform: 'node'`, `platform: 'browser'`
[option-platform](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-platform.md)

Tree shaking
`treeshake: true`, custom options
[option-tree-shaking](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-tree-shaking.md)

Minification
`minify: true`, `minify: 'dce-only'`
[option-minification](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-minification.md)

Source maps
`sourcemap: true`, `'inline'`, `'hidden'`
[option-sourcemap](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-sourcemap.md)

Watch mode
`watch: true`, watch options
[option-watch-mode](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-watch-mode.md)

Cleaning
`clean: true`, clean patterns
[option-cleaning](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-cleaning.md)

Log level
`logLevel: 'silent'`, `failOnWarn: false`
[option-log-level](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-log-level.md)

## Dependency Handling

Feature
Usage
Reference

Never bundle
`deps: { neverBundle: ['react', /^@myorg\//] }`
[option-dependencies](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-dependencies.md)

Always bundle
`deps: { alwaysBundle: ['dep-to-bundle'] }`
[option-dependencies](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-dependencies.md)

Only bundle
`deps: { onlyBundle: ['cac', 'bumpp'] }` - Whitelist
[option-dependencies](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-dependencies.md)

Skip node_modules
`deps: { skipNodeModulesBundle: true }`
[option-dependencies](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-dependencies.md)

Auto external
Automatic peer/dependency externalization
[option-dependencies](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-dependencies.md)

## Output Enhancement

Feature
Usage
Reference

Shims
`shims: true` - Add ESM/CJS compatibility
[option-shims](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-shims.md)

CJS default
`cjsDefault: true` (default) / `false`
[option-cjs-default](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-cjs-default.md)

Package exports
`exports: true` - Auto-generate exports field
[option-package-exports](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-package-exports.md)

CSS handling
**[experimental]** `css: { ... }` — full pipeline with preprocessors, Lightning CSS, PostCSS, code splitting; requires `@tsdown/css`
[option-css](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-css.md)

CSS inject
`css: { inject: true }` — preserve CSS imports in JS output
[option-css](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-css.md)

Unbundle mode
`unbundle: true` - Preserve directory structure
[option-unbundle](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-unbundle.md)

Root directory
`root: 'src'` - Control output directory mapping
[option-root](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-root.md)

Executable
**[experimental]** `exe: true` - Bundle as standalone executable, cross-platform via `@tsdown/exe`
[option-exe](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-exe.md)

Package validation
`publint: true`, `attw: true` - Validate package
[option-lint](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/option-lint.md)

## Framework & Runtime Support

Framework
Guide
Reference

React
JSX transform, React Compiler
[recipe-react](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/recipe-react.md)

Vue
SFC support, JSX
[recipe-vue](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/recipe-vue.md)

Solid
SolidJS JSX transform
[recipe-solid](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/recipe-solid.md)

Svelte
Svelte component libraries (source distribution recommended)
[recipe-svelte](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/recipe-svelte.md)

WASM
WebAssembly modules via `rolldown-plugin-wasm`
[recipe-wasm](https://github.com/antfu/skills/blob/HEAD/skills/tsdown/references/recipe-wasm.md)

## 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 tsconfig


## Best 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' }

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