Skip to main content
Bun is an all-in-one toolkit for JavaScript and TypeScript apps. It ships as a single executable called bun. At its core is the Bun runtime, a fast JavaScript runtime designed as a drop-in replacement for Node.js. It’s written in Zig and powered by JavaScriptCore — the engine Apple builds for Safari — which gives it dramatically faster startup times and lower memory usage compared to Node.js. 
bun run index.tsx  # TypeScript and JSX supported out of the box

​
What’s in the box

bun is a single binary that replaces an entire toolchain. Use it to run, install, build, and test your JavaScript and TypeScript projects.

Runtime

Execute JavaScript and TypeScript files with near-zero overhead. Drop-in replacement for Node.js with full compatibility for built-in modules and globals.

Package manager

Install packages up to 30x faster than npm using a global cache. Supports workspaces, overrides, and lockfiles.

Bundler

Bundle TypeScript, JSX, CSS, and HTML for browsers and servers. Tree-shaking, code splitting, and plugins included.

Test runner

Jest-compatible test runner with TypeScript support, snapshots, mocks, DOM testing, and watch mode built in.

​
Common commands

bun run index.tsx         # run a TypeScript or JavaScript file
bun run start             # run the "start" script from package.json
bun install               # install all dependencies
bun add figlet            # add a package
bun build ./index.tsx     # bundle a project for the browser
bun test                  # run tests
bunx cowsay 'Hello!'      # execute a package without installing it

​
Performance

Bun processes start 4x faster than Node.js on Linux. This is a direct result of using JavaScriptCore instead of V8, and writing the runtime in Zig — a systems language that compiles to tight, predictable machine code with no hidden allocations.
CommandStartup time
bun hello.js5.2ms
node hello.js25.1ms
Benchmark: simple Hello World script on Linux.

​
What is a runtime?

JavaScript (ECMAScript) is a specification, not an implementation. A JavaScript engine ingests a valid JS program and executes it. The two most popular engines today are V8 (used by Node.js and Chrome) and JavaScriptCore (used by Safari and Bun). Both are open source. A runtime wraps an engine and adds APIs that let programs interact with the outside world — the file system, network, environment variables, and so on. Node.js pioneered JavaScript on the server by adding APIs like fs, net, http, and the process global. Bun is a modern replacement: it implements those same Node.js APIs for compatibility, while also exposing the standard Web APIs (fetch, WebSocket, ReadableStream) that browsers use.

​
Design goals

Bun is designed from the ground up with today’s JavaScript ecosystem in mind.
  • Speed. Startup is 4x faster than Node.js. Package installs are up to 30x faster than npm.
  • TypeScript and JSX out of the box. You can execute .ts, .tsx, and .jsx files directly. Bun’s transpiler converts them to plain JavaScript before execution — no tsc or Babel required.
  • ESM and CommonJS compatibility. Bun recommends ES modules, but fully supports CommonJS. You can import and require in the same file.
  • Web-standard APIs. fetch, WebSocket, URL, Headers, ReadableStream — all built in, using Safari’s own WebCore implementations where possible.
  • Node.js compatibility. Bun implements Node.js built-in modules (path, fs, http, crypto, etc.) and globals (process, Buffer, __dirname) so existing Node.js projects run with little or no changes.
Node.js compatibility is an ongoing effort. Check the compatibility page for the current status of individual APIs and modules.

​
Next steps

Installation

Install Bun on macOS, Linux, or Windows.

Quickstart

Build a working HTTP server in under 5 minutes.

TypeScript

Learn how Bun handles TypeScript natively.

Runtime overview

Explore what the Bun runtime can do.

Build docs developers (and LLMs) love

Get started for freeTalk to us