Tsdown

tsdown - The Elegant Library Bundler

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

Runtime Requirement

tsdown requires Node.js 22.18.0 or higher to run (build-time only). However, the bundled output can target much lower Node.js versions via the [target](references/option-target.md) option, so libraries built with tsdown are not locked to Node.js 22+ at runtime.

If your package needs to support Node.js 18 / 20:

• Build with Node.js 22+ in CI (e.g. set target: 'node18' or target: 'node20').
• Test the built output (or the packed tarball) on the lower Node.js versions you intend to support — e.g. using a matrix job that runs the published package's tests on Node.js 18 / 20 / 22.

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](references/guide-getting-started.md) | | Configuration File | Config file formats, multiple configs, workspace | [option-config-file](references/option-config-file.md) | | CLI Reference | All CLI commands and options | [reference-cli](references/reference-cli.md) | | Migrate from tsup | Migration guide and compatibility notes | [guide-migrate-from-tsup](references/guide-migrate-from-tsup.md) | | Plugins | Rolldown, Rollup, Unplugin support | [advanced-plugins](references/advanced-plugins.md) |

> For comprehensive migration assistance with complete option mappings, install the dedicated [tsdown-migrate](../tsdown-migrate/SKILL.md) skill: npx skills add rolldown/tsdown --skill tsdown-migrate | Hooks | Lifecycle hooks for custom logic | [advanced-hooks](references/advanced-hooks.md) | | Programmatic API | Build from Node.js scripts | [advanced-programmatic](references/advanced-programmatic.md) | | Rolldown Options | Pass options directly to Rolldown | [advanced-rolldown-options](references/advanced-rolldown-options.md) | | CI Environment | CI detection, 'ci-only' / 'local-only' values | [advanced-ci](references/advanced-ci.md) |

Build Options

| Option | Usage | Reference | |--------|-------|-----------| | Entry points | entry: ['src/*.ts', '!**/*.test.ts'] | [option-entry](references/option-entry.md) | | Output formats | format: ['esm', 'cjs', 'iife', 'umd'] | [option-output-format](references/option-output-format.md) | | Output directory | outDir: 'dist', outExtensions | [option-output-directory](references/option-output-directory.md) | | Type declarations | dts: true, dts: { sourcemap, compilerOptions, vue } | [option-dts](references/option-dts.md) | | Target environment | target: 'es2020', target: 'esnext' | [option-target](references/option-target.md) | | Platform | platform: 'node', platform: 'browser' | [option-platform](references/option-platform.md) | | Tree shaking | treeshake: true, custom options | [option-tree-shaking](references/option-tree-shaking.md) | | Minification | minify: true, minify: 'dce-only' | [option-minification](references/option-minification.md) | | Source maps | sourcemap: true, 'inline', 'hidden' | [option-sourcemap](references/option-sourcemap.md) | | Watch mode | watch: true, watch options | [option-watch-mode](references/option-watch-mode.md) | | Cleaning | clean: true, clean patterns | [option-cleaning](references/option-cleaning.md) | | Log level | logLevel: 'silent', failOnWarn: false | [option-log-level](references/option-log-level.md) |

Dependency Handling

| Feature | Usage | Reference | |---------|-------|-----------| | Never bundle | deps: { neverBundle: ['react', /^@myorg\//] } | [option-dependencies](references/option-dependencies.md) | | Always bundle | deps: { alwaysBundle: ['dep-to-bundle'] } | [option-dependencies](references/option-dependencies.md) | | Only bundle | deps: { onlyBundle: ['cac', 'bumpp'] } - Whitelist | [option-dependencies](references/option-dependencies.md) | | Skip node_modules | deps: { skipNodeModulesBundle: true } | [option-dependencies](references/option-dependencies.md) | | Auto external | Automatic dependency/peer/optional externalization | [option-dependencies](references/option-dependencies.md) |

Output Enhancement

| Feature | Usage | Reference | |---------|-------|-----------| | Shims | shims: true - Add ESM/CJS compatibility | [option-shims](references/option-shims.md) | | CJS default | cjsDefault: true (default) / false | [option-cjs-default](references/option-cjs-default.md) | | Package exports | exports: true - Generate exports field | [option-package-exports](references/option-package-exports.md) | | CSS handling | [experimental] css: { ... } — full pipeline with preprocessors, Lightning CSS, PostCSS, CSS modules, code splitting; requires @tsdown/css | [option-css](references/option-css.md) | | CSS modules | css: { modules: { localsConvention: 'camelCase' } } — scoped class names for .module.css files | [option-css](references/option-css.md) | | CSS inject | css: { inject: true } — preserve CSS imports in JS output | [option-css](references/option-css.md) | | Unbundle mode | unbundle: true - Preserve directory structure | [option-unbundle](references/option-unbundle.md) | | Root directory | root: 'src' - Control output directory mapping | [option-root](references/option-root.md) | | Executable | [experimental] exe: true - Bundle as standalone executable, cross-platform via @tsdown/exe | [option-exe](references/option-exe.md) | | Package validation | publint: true, attw: true - Validate package | [option-lint](references/option-lint.md) |

Framework & Runtime Support

| Framework | Guide | Reference | |-----------|-------|-----------| | React | JSX transform, React Compiler | [recipe-react](references/recipe-react.md) | | Vue | SFC support, JSX | [recipe-vue](references/recipe-vue.md) | | Solid | SolidJS JSX transform | [recipe-solid](references/recipe-solid.md) | | Svelte | Svelte component libraries (source distribution recommended) | [recipe-svelte](references/recipe-svelte.md) | | WASM | WebAssembly modules via rolldown-plugin-wasm | [recipe-wasm](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

1. Always generate type declarations for TypeScript libraries:

``ts { dts: true } ``

1. Externalize dependencies to avoid bundling unnecessary code:

``ts { deps: { neverBundle: [/^react/, /^@myorg\//] } } ``

1. Use tree shaking for optimal bundle size:

``ts { treeshake: true } ``

1. Enable minification for production builds:

``ts { minify: true } ``

1. Add shims for better ESM/CJS compatibility:

``ts { shims: true } // Adds __dirname, __filename, etc. ``

1. Auto-generate package.json exports:

``ts { exports: true } // Creates proper exports field ``

1. Use watch mode during development:

``bash tsdown --watch ``

1. Preserve structure for utilities with many files:

``ts { unbundle: true } // Keep directory structure ``

1. Validate packages in CI before publishing:

``ts { publint: 'ci-only', attw: 'ci-only' } ``

Resources

• Documentation: https://tsdown.dev
• GitHub: https://github.com/rolldown/tsdown
• Rolldown: https://rolldown.rs
• Migration Guide: https://tsdown.dev/guide/migrate-from-tsup

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: antfu
• Source: antfu/skills
• License: MIT

Install and usage instructions live in the source repository linked above.