---
id: hairyf/skills/tsdown
version: "4e823da6"
license: MIT
install: manual
updated: 2026-06-10
---

# tsdown — tsdown is a bundling tool designed to package TypeScript and JavaScript libraries for npm distribution with support for multiple output formats. It simplifies the build process by offering flexible configuration options tailored to modern web development workflows.

Publisher: hairyf · Stars: 24 · Updated: 2026-06-10

Install (manual): `git clone https://github.com/hairyf/skills`

## SKILL.md

# 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

```bash
# 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

```ts
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

```ts
export default defineConfig({
  entry: ['src/index.ts'],
  format: ['esm', 'cjs'],
  dts: true,
  clean: true,
})
```

### Multiple Entry Points

```ts
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)

```ts
export default defineConfig({
  entry: ['src/index.ts'],
  format: ['iife'],
  globalName: 'MyLib',
  platform: 'browser',
  minify: true,
})
```

### React Component Library

```ts
export default defineConfig({
  entry: ['src/index.tsx'],
  format: ['esm', 'cjs'],
  dts: true,
  deps: {
    neverBundle: ['react', 'react-dom'],
  },
  inputOptions: {
    jsx: { runtime: 'automatic' },
  },
})
```

### Preserve Directory Structure

```ts
export default defineConfig({
  entry: ['src/**/*.ts', '!**/*.test.ts'],
  unbundle: true, // Preserve file structure
  format: ['esm'],
  dts: true,
})
```

### CI-Aware Configuration

```ts
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

```ts
import { wasm } from 'rolldown-plugin-wasm'
import { defineConfig } from 'tsdown'

export default defineConfig({
  entry: ['src/index.ts'],
  plugins: [wasm()],
})
```

### Library with CSS and Sass

```ts
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

```ts
export default defineConfig({
  entry: ['src/cli.ts'],
  exe: true,
})
```

### Cross-Platform Executable (requires `@tsdown/exe`)

```ts
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

```ts
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:

```ts
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:

```ts
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:

```ts
export default defineConfig({
  workspace: 'packages/*',
  entry: ['src/index.ts'],
  format: ['esm', 'cjs'],
  dts: true,
})
```

## CLI Quick Reference

```bash
# 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 }
   ```

2. **Externalize dependencies** to avoid bundling unnecessary code:
   ```ts
   { deps: { neverBundle: [/^react/, /^@myorg\//] } }
   ```

3. **Use tree shaking** for optimal bundle size:
   ```ts
   { treeshake: true }
   ```

4. **Enable minification** for production builds:
   ```ts
   { minify: true }
   ```

5. **Add shims** for better ESM/CJS compatibility:
   ```ts
   { shims: true }  // Adds __dirname, __filename, etc.
   ```

6. **Auto-generate package.json exports**:
   ```ts
   { exports: true }  // Creates proper exports field
   ```

7. **Use watch mode** during development:
   ```bash
   tsdown --watch
   ```

8. **Preserve structure** for utilities with many files:
   ```ts
   { unbundle: true }  // Keep directory structure
   ```

9. **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


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