Bun is an incredibly fast all-in-one JavaScript runtime, bundler, test runner, and package manager designed to replace Node.js, webpack, Babel, yarn, and more with a single, cohesive tool. Built from scratch in Zig and powered by JavaScriptCore (Safari's JavaScript engine), Bun delivers performance that's orders of magnitude faster than traditional JavaScript tooling.
As a runtime, Bun is a drop-in replacement for Node.js that implements Node.js APIs and adds many enhancements. It starts up to 4x faster than Node.js and runs JavaScript/TypeScript code with exceptional performance. Bun natively supports TypeScript and JSX without requiring any transpilation step, eliminating the need for separate build tools during development.
Bun's built-in bundler is dramatically faster than webpack, esbuild, or Parcel, capable of bundling projects in milliseconds rather than seconds. The bundler supports code splitting, tree shaking, minification, and all modern bundling features out of the box. It also includes a built-in transpiler that handles TypeScript, JSX, and modern JavaScript syntax without external dependencies.
The package manager is one of Bun's standout features, installing npm packages up to 30x faster than npm and 20x faster than pnpm. It's compatible with the npm registry and package.json format, making migration from existing Node.js projects seamless. Bun's package manager also includes a global cache that saves disk space and speeds up installations across projects.
Bun includes a built-in test runner that's significantly faster than Jest or Vitest, with a familiar API that makes migration straightforward. The test runner supports mocking, snapshots, code coverage, and watch mode, providing everything needed for comprehensive testing without additional dependencies.
With built-in support for Web APIs (fetch, WebSocket, Streams), environment variables, hot reloading, and SQLite, Bun provides a batteries-included experience that eliminates the need for numerous third-party packages. Whether you're building APIs, full-stack applications, CLI tools, or microservices, Bun offers a modern, fast, and delightful developer experience.