---
id: rolldown/tsdown/tsdown-migrate
version: "a9244beb"
license: MIT
install: manual
updated: 2026-07-27
---

# tsdown-migrate — This skill guides you through converting an existing tsup-based build setup to tsdown, Rolldown's elegant library bundler. It provides comprehensive option mappings and automated config transformation to ensure your project transitions smoothly while maintaining build performance and output quality.

Publisher: rolldown · Stars: 4183 · Updated: 2026-07-27

Install (manual): `git clone https://github.com/rolldown/tsdown`

## SKILL.md

# Migrating from tsup to tsdown

Knowledge base for AI agents to migrate tsup projects to tsdown — the Rolldown-powered library bundler.

## Target Version: Two-Stage Migration

tsdown v0.23 removed all previously-deprecated tsup compatibility options — `bundle`, `outExtension`, `publicDir`, `removeNodeProtocol`, `injectStyle`, and `skipNodeModulesBundle` are no longer recognized. They fail TypeScript type checking and are **silently ignored at runtime**, so a missed mapping on v0.23+ produces wrong output without any error. Migrating directly to v0.23+ is therefore unsafe. tsdown **v0.22.14** is the last version that still accepts these options and flags each one with a deprecation warning, making it the safe migration checkpoint. Migrate in **two stages**:

1. **Stage 1 — migrate on `tsdown@0.22.14`**: Install `tsdown@0.22.14`, migrate the config per the tables below, run a build, and resolve **every** deprecation warning by mapping each flagged tsup option to its real tsdown equivalent. The warnings are the completeness check — the migration is not done until the build produces **zero warnings**.
2. **Stage 2 — upgrade to the latest tsdown (`^0.23.0` or newer)**: Only after a warning-free build on 0.22.14. Since the config no longer uses any removed compat options, the silent-ignore behavior of v0.23+ is no longer a risk.

## Runtime Requirement

`tsdown` requires **Node.js `^22.18.0 || ^24.11.0 || >=26.0.0` to run** (build-time only) — that is, Node.js 22.18+, 24.11+, or 26+. Odd-numbered and EOL release lines (e.g. Node.js 23, 25) are not supported. The bundled output can still target lower Node.js versions via the [`target`](../tsdown/references/option-target.md) option, so a library that previously supported Node.js 18 / 20 with tsup can continue to do so after migrating.

Recommended workflow when supporting Node.js 18 / 20:

- **Build with Node.js 22+ in CI**, setting an explicit `target` such as `'node18'` or `'node20'`.
- **Test the built output (or the packed tarball) on the lower Node.js versions** you need to support.

## When to Use

- Migrating a project from tsup to tsdown
- Understanding differences between tsup and tsdown options
- Reviewing or fixing post-migration configuration issues
- Advising users on tsup→tsdown compatibility

## Migration Overview

Follow these steps to migrate a tsup project:

1. **Rename config file**: `tsup.config.*` → `tsdown.config.*`
2. **Update imports**: `'tsup'` → `'tsdown'`
3. **Apply option mappings**: Rename/transform options per tables below
4. **Preserve tsup defaults**: Explicitly set options that differ (format, clean, dts, target)
5. **Update package.json**: Dependencies (Stage 1: `tsdown@0.22.14`), scripts, root config field
6. **Remove unsupported options**: Replace with alternatives where available
7. **Test build on 0.22.14**: Run `tsdown` and resolve every deprecation warning — zero warnings required
8. **Upgrade to latest tsdown** (`^0.23.0` or newer) and verify the build again

## Config File Migration

### File Rename

| tsup | tsdown |
|------|--------|
| `tsup.config.ts` | `tsdown.config.ts` |
| `tsup.config.cts` | `tsdown.config.cts` |
| `tsup.config.mts` | `tsdown.config.mts` |
| `tsup.config.js` | `tsdown.config.js` |
| `tsup.config.cjs` | `tsdown.config.cjs` |
| `tsup.config.mjs` | `tsdown.config.mjs` |
| `tsup.config.json` | `tsdown.config.json` |

### Import and Identifier Changes

```ts
// Before
import { defineConfig } from 'tsup'

// After
import { defineConfig } from 'tsdown'
```

Replace all identifiers: `tsup` → `tsdown`, `TSUP` → `TSDOWN`.

## Option Mappings

### Property Renames

| tsup | tsdown | Notes |
|------|--------|-------|
| `entryPoints` | `entry` | Also deprecated in tsup itself |
| `cjsInterop` | `cjsDefault` | CJS default export handling |
| `esbuildPlugins` | `plugins` | Now uses Rolldown/Unplugin plugins |
| `outExtension` | `outExtensions` | Custom output extensions |
| `publicDir` | `copy` | Copy static files to output |
| `bundle: true` | _(remove)_ | Bundle is default behavior |
| `bundle: false` | `unbundle: true` | Preserve file structure |
| `removeNodeProtocol: true` | `nodeProtocol: 'strip'` | Strip `node:` prefix |
| `injectStyle: true` | `css: { inject: true }` | CSS injection |
| `injectStyle: false` | _(remove)_ | Default behavior |
| `skipNodeModulesBundle` | `deps: { neverBundle: true }` | Externalize all dependencies |

None of the old names are recognized by tsdown v0.23+ — always emit the new names. The compatibility options (`outExtension`, `skipNodeModulesBundle`, `publicDir`, `bundle`, `removeNodeProtocol`, `injectStyle`) were accepted with deprecation warnings up to v0.22.14 and removed entirely in v0.23; on v0.23+ leftovers are silently ignored, not errors, so builds misbehave without warning. This is why Stage 1 runs on v0.22.14, where every leftover is flagged.

### Deprecated but Still Accepted

`external` and `noExternal` are the **only** tsup option names tsdown v0.23 still accepts. They emit deprecation warnings, will be removed in a future version, and cannot be combined with their replacements (mixing `external` with `deps.neverBundle`, or `noExternal` with `deps.alwaysBundle`, throws an error). Always emit the replacements.

| tsup (deprecated) | tsdown (preferred) | Notes |
|--------------------|--------------------|-------|
| `external: [...]` | `deps: { neverBundle: [...] }` | Moved to deps namespace |
| `noExternal: [...]` | `deps: { alwaysBundle: [...] }` | Moved to deps namespace |

### Output Filename Differences

For IIFE builds, `tsdown` emits names like `[name].iife.js`, while `tsup` commonly emitted `[name].global.js`. `outExtensions` customizes extensions or suffixes, but it does not remove the built-in `.iife` or `.umd` segment. Use `outputOptions.entryFileNames: '[name].global.js'` to preserve old IIFE filenames.

### Dependency Namespace Moves

Dependencies config moved under `deps` namespace. If both `external` and `noExternal` exist, merge into a single `deps` object:

```ts
// Before (tsup)
export default defineConfig({
  external: ['react'],
  noExternal: ['lodash-es'],
})

// After (tsdown)
export default defineConfig({
  deps: {
    neverBundle: ['react'],
    alwaysBundle: ['lodash-es'],
  },
})
```

tsdown also adds `deps.onlyBundle` (whitelist of allowed bundled packages) — no tsup equivalent.

Dependency handling defaults in tsdown v0.23+:

- `dependencies`, `peerDependencies`, and **`optionalDependencies`** are all externalized by default (tsup only externalizes `dependencies` and `peerDependencies`, so `optionalDependencies` may switch from bundled to external after migration).
- `deps.resolveDepSubpath` (resolving subpath imports of externalized packages without an `exports` field) is **disabled by default**.

### Plugin Import Transforms

```ts
// Before (tsup - esbuild plugins)
import plugin from 'unplugin-example/esbuild'

// After (tsdown - Rolldown plugins)
import plugin from 'unplugin-example/rolldown'
```

All `unplugin-*/esbuild` imports should change to `unplugin-*/rolldown`.

For complete before/after examples of every transformation, see [guide-option-mappings.md](references/guide-option-mappings.md).

## Default Value Differences

tsdown changes several defaults from tsup. When migrating, explicitly set these to preserve tsup behavior, then let the user decide which new defaults to adopt.

| Option | tsup Default | tsdown Default | Migration Action |
|--------|-------------|----------------|-----------------|
| `format` | `'cjs'` | `'esm'` | Set `format: 'cjs'` to preserve |
| `clean` | `false` | `true` | Set `clean: false` to preserve |
| `dts` | `false` | Auto-enabled if `types`/`typings` in package.json | Set `dts: false` to preserve |
| `target` | _(none)_ | Auto-reads from `engines.node` in package.json | Set `target: false` to preserve |

After migration, suggest the user review these — tsdown's defaults are generally better:
- ESM is the modern standard
- Cleaning output prevents stale files
- Auto DTS from package.json reduces config
- Auto target from engines.node ensures consistency

## Unsupported Options

These tsup options have no direct equivalent in tsdown. Remove them and inform the user.

| tsup Option | Status | Alternative |
|-------------|--------|-------------|
| `splitting` | Always enabled | Remove — code splitting cannot be disabled in tsdown |
| `metafile` | Not available | Suggest `devtools: true` for Vite DevTools bundle analysis |
| `swc` | Not supported | Remove — tsdown uses oxc for transformation (built-in) |
| `experimentalDts` | Not supported | Use the `dts` option instead |
| `legacyOutput` | Not supported | Remove — no alternative |
| `plugins` (tsup experimental) | Incompatible | Migrate to Rolldown plugins manually; tsup's plugin API differs from Rolldown's |

## Package.json Migration

### Scripts

Replace `tsup` and `tsup-node` with `tsdown` in all script commands:

```json
// Before
{
  "scripts": {
    "build": "tsup src/index.ts",
    "dev": "tsup --watch"
  }
}

// After
{
  "scripts": {
    "build": "tsdown src/index.ts",
    "dev": "tsdown --watch"
  }
}
```

### Dependencies

| Location | Action |
|----------|--------|
| `dependencies.tsup` | Rename to `dependencies.tsdown` |
| `devDependencies.tsup` | Rename to `devDependencies.tsdown` |
| `optionalDependencies.tsup` | Rename to `optionalDependencies.tsdown` |
| `peerDependencies.tsup` | Rename to `peerDependencies.tsdown` |
| `peerDependenciesMeta.tsup` | Rename to `peerDependenciesMeta.tsdown` |

### Root Config Field

If package.json has a root-level `tsup` field (inline config), rename to `tsdown`:

```json
// Before
{ "tsup": { "entry": ["src/index.ts"] } }

// After
{ "tsdown": { "entry": ["src/index.ts"] } }
```

For detailed package.json examples, see [guide-package-json.md](references/guide-package-json.md).

## New tsdown Features

After migration, suggest these tsdown-exclusive features to the user:

| Feature | Config | Description |
|---------|--------|-------------|
| Node protocol | `nodeProtocol: true \| 'strip'` | Add or strip `node:` prefix on built-in imports |
| Workspace | `workspace: 'packages/*'` | Build multiple packages in a monorepo |
| Package exports | `exports: true` | Auto-generate `exports` field in package.json |
| Package validation | `publint: true`, `attw: true` | Lint package and check type correctness |
| Executable | `exe: true` | Bundle as Node.js standalone executable (SEA) |
| DevTools | `devtools: true` | Vite DevTools integration for bundle analysis |
| Hooks | `hooks: { 'build:done': ... }` | Lifecycle hooks: `build:prepare`, `build:before`, `build:done` |
| CSS modules | `css: { modules: { ... } }` | Scoped class names for `.module.css` files |
| Glob import | `globImport: true` | Support `import.meta.glob` (Vite-style) |

For detailed comparisons, see [guide-differences-detailed.md](references/guide-differences-detailed.md).

## References

| Topic | Description | Reference |
|-------|-------------|-----------|
| Option Mappings | Complete before/after for every option transform | [guide-option-mappings](references/guide-option-mappings.md) |
| Detailed Differences | Architecture, features, compatibility comparison | [guide-differences-detailed](references/guide-differences-detailed.md) |
| Package.json | Dependency, script, and config field migration | [guide-package-json](references/guide-package-json.md) |

## Migration Checklist

Use this checklist when performing a migration:

```
- [ ] Rename tsup.config.* → tsdown.config.*
- [ ] Update import from 'tsup' to 'tsdown'
- [ ] Replace tsup/TSUP identifiers with tsdown/TSDOWN
- [ ] Apply property renames (cjsInterop→cjsDefault, esbuildPlugins→plugins, outExtension→outExtensions, publicDir→copy, bundle→unbundle, removeNodeProtocol→nodeProtocol, injectStyle→css.inject)
- [ ] Move external/noExternal into deps namespace, replace skipNodeModulesBundle with `deps.neverBundle: true`
- [ ] Update unplugin imports from /esbuild to /rolldown
- [ ] Set explicit defaults to preserve tsup behavior (format, clean, dts, target)
- [ ] Remove unsupported options (splitting, metafile, swc, etc.)
- [ ] Update package.json scripts (tsup→tsdown)
- [ ] Update package.json dependencies (Stage 1: tsdown@0.22.14)
- [ ] Rename root-level tsup config field if present
- [ ] Run tsdown on 0.22.14 and resolve every deprecation warning (zero warnings required)
- [ ] Upgrade to the latest tsdown (^0.23.0 or newer) and verify the build again
- [ ] Suggest new tsdown features to the user
```


[View on SkillFed](https://skillfed.io/rolldown/tsdown/tsdown-migrate) · [View on GitHub](https://github.com/rolldown/tsdown)