An all-in-one JavaScript toolkit — runtime, package manager, bundler, and test runner in a single binary.
Bun is a JavaScript runtime built from scratch in Zig, designed as a faster, more cohesive replacement for the Node.js + npm + esbuild + Jest stack. It runs JavaScript and TypeScript out of the box without a separate transpile step, ships with its own package manager that is a drop-in replacement for npm/yarn/pnpm, and includes a bundler, a test runner, and a SQLite client — all in a single `bun` binary. In real-world benchmarks, Bun installs dependencies 20–30x faster than npm and runs server-side code roughly 2–3x faster than Node on common HTTP workloads. It implements most of the Node API and the Web standard APIs, so existing libraries usually work without changes. As of 2026 it is production-ready for many workloads, though some long-tail native modules and edge cases in the Node ecosystem still favor staying on Node.
Runs `.ts` files directly with no separate compile step.
Implements `fs`, `path`, `http`, `node:crypto` and most of the Node API surface.
20–30x faster installs than npm, fully compatible with `package.json`.
Bundles JS/TS/CSS for the browser and server, no Webpack/Vite needed for many cases.
`bun test` runs Jest-style tests with native TypeScript and JSX support.
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Switched our CI to Bun last month. Build times went from 12 minutes to 3. Sold.