# Tsdown

> Bundle TypeScript and JavaScript libraries with blazing-fast speed powered by Rolldown. Use when building libraries, generating type declarations, bundling for multiple formats, or migrating from tsup.

- Skill: `ehyland/tsdown` (Agent Skill, multi-file: 36 files)
- Install (CLI): `npx skillmds@latest add ehyland/tsdown`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ehyland/tsdown/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: ehyland (https://skillmd.com/u/ehyland)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/ehyland/tsdown

---


# 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

```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)                   |
| 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: 'ci-only'`           | [option-log-level](./references/option-log-level.md)               |

## Dependency Handling

| Feature       | Usage                                     | Reference                                                  |
| ------------- | ----------------------------------------- | ---------------------------------------------------------- |
| External deps | `external: ['react', /^@myorg\//]`        | [option-dependencies](./references/option-dependencies.md) |
| Inline deps   | `noExternal: ['dep-to-bundle']`           | [option-dependencies](./references/option-dependencies.md) |
| Auto external | Automatic peer/dependency 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` - Auto-generate exports field    | [option-package-exports](./references/option-package-exports.md) |
| CSS handling       | **[experimental]** Still in development          | [option-css](./references/option-css.md)                         |
| Unbundle mode      | `unbundle: true` - Preserve directory structure  | [option-unbundle](./references/option-unbundle.md)               |
| Package validation | `publint: true`, `attw: true` - Validate package | [option-lint](./references/option-lint.md)                       |

## Framework & Runtime Support

| Framework | Guide                                          | Reference                                    |
| --------- | ---------------------------------------------- | -------------------------------------------- |
| React     | JSX transform, Fast Refresh                    | [recipe-react](./references/recipe-react.md) |
| Vue       | SFC support, JSX                               | [recipe-vue](./references/recipe-vue.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,
  external: ["react", "react-dom"],
  plugins: [
    // React Fast Refresh support
  ],
});
```

### 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",
  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()],
});
```

### 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 --outDir lib            # Custom output directory
tsdown --minify                # Enable minification
tsdown --dts                   # Generate declarations

# Entry options
tsdown src/index.ts            # Single entry
tsdown src/*.ts                # Glob patterns
tsdown src/a.ts src/b.ts       # Multiple entries

# Development
tsdown --watch                 # Watch mode
tsdown --sourcemap             # Generate source maps
tsdown --clean                 # Clean output directory
```

## Best Practices

1. **Always generate type declarations** for TypeScript libraries:

   ```ts
   {
     dts: true;
   }
   ```

2. **Externalize dependencies** to avoid bundling unnecessary code:

   ```ts
   {
     external: [/^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