tsdown is a library bundler that uses a Rust-native core, built on Rolldown and the Oxc parser, to compile TypeScript and JavaScript source code into optimized output files. It is designed to produce bundles in multiple formats—ESM, CJS, IIFE, and UMD—from a single source, and automatically generates TypeScript declaration files during the build process for type-safe distribution.
The project distinguishes itself by offering a plugin system compatible with Rollup, Rolldown, unplugin, and some Vite plugins, allowing the build pipeline to be extended with custom transformations. It also accepts tsup's main options and features, enabling existing projects to migrate without rewriting their configuration. The bundler provides a zero-config setup that bundles source code and generates declarations without manual configuration.
The tool handles non-code assets like JSON and WebAssembly files, and its output pipeline is configurable for different module system targets. Documentation and installation details are available through the project's repository.