Rolldown is a bundler for JavaScript and TypeScript, written in the Rust language. A bundler reads the many source files and npm packages of a web application, follows their imports, and writes a few optimized output files that a browser loads quickly. Rolldown is a project of VoidZero Inc. and its open-source contributors, and it is the bundler inside Vite 8 and later.
Its programming interface and plugin interface are compatible with Rollup, an older JavaScript bundler, so many Rollup plugins and options work with it. Like esbuild, another fast bundler, it has built-in transforms, minification (removing spaces and shortening names to make files smaller) and code splitting. On the project's benchmark of 19,000 modules it bundled in 1.61 seconds, against 40.10 seconds for Rollup with esbuild. Most applications use it through Vite; developers can also install it from npm and call it directly, with prebuilt binaries for Linux, Windows and macOS and a WebAssembly build for other platforms.
Rolldown is free and open source under the MIT License.