tsdown is a high-performance, elegant library bundler designed for the modern JavaScript and TypeScript ecosystem. Built by VoidZero Inc., it acts as an official library-focused tool powered by Rolldown, a cutting-edge bundler written in Rust. While Rolldown provides a powerful general-purpose engine, tsdown builds on this foundation by offering an out-of-the-box solution specifically tailored to the needs of library authors, minimizing complex configurations and maximizing productivity. It serves as an essential tool for developers who prioritize speed, reliability, and developer experience when creating libraries.

At its core, tsdown streamlines the library development process by handling tasks such as bundling TypeScript and JavaScript files, generating declaration files, and supporting multiple output formats. It is designed to be a drop-in upgrade for users of existing tools like tsup, ensuring a seamless migration path while delivering significant performance improvements. By leveraging Oxc and Rolldown for its compilation and bundling, tsdown achieves lightning-fast build times even for complex, large-scale projects.

Some of the key features are:

• High-Performance Build Engine: Powered by Rust-based Rolldown and Oxc to provide blazing-fast bundling and declaration generation.
• Library-Optimized: Specifically designed for building libraries with automatic TypeScript declaration file (.d.ts) generation.
• Extensive Plugin Compatibility: Full support for the Rolldown plugin ecosystem, as well as compatibility with many existing Rollup, unplugin, and Vite plugins.
• Out-of-the-Box Experience: Comes preconfigured with sensible defaults for common library tasks, reducing the need for boilerplate setup.
• Seamless tsup Migration: Designed to be compatible with tsup’s main options and features, ensuring a smooth transition for existing projects.
• Monorepo and Workspace Support: Built-in support for monorepos, allowing for efficient management and building of multiple packages.
• Modern Features: Includes built-in support for CSS, single executable applications (SEA), and comprehensive package validation.

Operating tsdown is designed to be straightforward. Developers typically integrate it into their project by installing it via npm and creating a configuration file. Because it preconfigures most common settings, users often find they need very little configuration to get started. The tool handles the complexities of build targets, module resolutions, and environment variable injections internally. For advanced needs, it exposes a flexible API and hooks, allowing for deep customization of the build process without sacrificing the simplicity of the CLI interface.

Some common use cases include:

• Library Development: Rapidly bundling and packaging TypeScript libraries with support for ESM, CJS, IIFE, and UMD formats for cross-environment compatibility.
• Monorepo Management: Efficiently building and publishing multiple interconnected packages within a single workspace.
• Modern Web Tooling: Integrating modern web development workflows by leveraging its support for various plugins and advanced build optimizations.
• Production Optimization: Utilizing built-in tree shaking, minification, and source map generation to ensure high-quality, production-ready output.