How it works
Bun is written in Zig and runs on JavaScriptCore, the engine from Safari, rather than V8. It runs TypeScript and JSX directly, starts quickly and replaces several tools at once: bun install for packages (much faster than npm), bun test for tests and bun build for bundling. It implements most Node.js APIs, so many Node apps and frameworks run on it unchanged.
It also has built-in extras that would be separate packages elsewhere: an HTTP server (Bun.serve), a SQLite driver, PostgreSQL and S3 clients, and password hashing. Anthropic acquired Bun in late 2025, and it remains open source under the MIT licence. Compatibility with Node is high but not complete, so test an app's dependencies before moving production traffic.
Bun pros and cons
Pros
- Installs packages and starts up noticeably faster than Node.js
- One tool replaces the runtime, package manager, bundler and test runner
- Runs TypeScript and JSX with no configuration
- Built-in SQLite, PostgreSQL and S3 clients
Cons
- Node.js compatibility is high but still has gaps
- Younger, with fewer years in production behind it
- Fewer hosts document it than Node.js
When to use Bun
Pick it when
- Faster installs and test runs in an existing JavaScript project
- New TypeScript servers and scripts that want minimal setup
Skip it when
- Dependencies rely on Node internals or native add-ons that Bun does not support yet
Bun pricing
Bun vs the alternatives
- Node.js vs Deno vs BunThree runtimes for JavaScript and TypeScript on the server. Much of the same code runs on all three; they differ in built-in tools, security defaults, speed and how long each has been used in production.
- npm vs pnpm vs Yarn vs BunAll four install packages from the same npm registry and read the same package.json. They differ in speed, disk use, strictness and what else comes bundled with them.
Related terms
More in Backend and APIs
Runtimes