tsdown

SKILL.md

Fast TypeScript/JavaScript library bundler powered by Rolldown with multi-format output and type declaration generation.

Supports bundling to ESM, CJS, IIFE, and UMD formats with automatic peer dependency externalization and tree shaking

Generates TypeScript declaration files (.d.ts) with source map and compiler option control, plus experimental CSS pipeline with preprocessor and PostCSS support

Includes watch mode, minification, source maps, unbundle mode for preserving directory structure, and framework-specific recipes for React, Vue, Solid, and Svelte

Offers CLI commands, programmatic API, lifecycle hooks, workspace/monorepo support, and direct Rolldown option passthrough for advanced customization

Provides migration tooling from tsup and experimental features for standalone executable bundling and package validation (publint, attw)

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