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 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

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

Dependency Handling

Output Enhancement

Framework & Runtime Support

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:

   {
     dts: true;
   }
   

2. Externalize dependencies to avoid bundling unnecessary code:

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

3. Use tree shaking for optimal bundle size:

   {
     treeshake: true;
   }
   

4. Enable minification for production builds:

   {
     minify: true;
   }
   

5. Add shims for better ESM/CJS compatibility:

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

6. Auto-generate package.json exports:

   {
     exports: true;
   } // Creates proper exports field
   

7. Use watch mode during development:

   tsdown --watch
   

8. Preserve structure for utilities with many files:

   {
     unbundle: true;
   } // Keep directory structure
   

9. Validate packages in CI before publishing:

   { 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