Bun itself is MIT-licensed.

## JavaScriptCore

Bun statically links JavaScriptCore (and WebKit) which is LGPL-2 licensed. WebCore files from WebKit are also licensed under LGPL2. Per LGPL2:

> (1) If you statically link against an LGPL’d library, you must also provide your application in an object (not necessarily source) format, so that a user has the opportunity to modify the library and relink the application.

You can find the patched version of WebKit used by Bun here: <https://github.com/oven-sh/webkit>. If you would like to relink Bun with changes:

- `git submodule update --init --recursive`
- `make jsc`
- `zig build`

This compiles JavaScriptCore, compiles Bun’s `.cpp` bindings for JavaScriptCore (which are the object files using JavaScriptCore) and outputs a new `bun` binary with your changes.

## Linked libraries

Bun statically links these libraries:

{% table %}

- Library
- License

---

- [`boringssl`](https://boringssl.googlesource.com/boringssl/)
- [several licenses](https://boringssl.googlesource.com/boringssl/+/refs/heads/master/LICENSE)

---

- [`libarchive`](https://github.com/libarchive/libarchive)
- [several licenses](https://github.com/libarchive/libarchive/blob/master/COPYING)

---

- [`lol-html`](https://github.com/cloudflare/lol-html/tree/master/c-api)
- BSD 3-Clause

---

- [`mimalloc`](https://github.com/microsoft/mimalloc)
- MIT

---

- [`picohttp`](https://github.com/h2o/picohttpparser)
- dual-licensed under the Perl License or the MIT License

---

- [`zstd`](https://github.com/facebook/zstd)
- dual-licensed under the BSD License or GPLv2 license

---

- [`simdutf`](https://github.com/simdutf/simdutf)
- Apache 2.0

---

- [`tinycc`](https://github.com/tinycc/tinycc)
- LGPL v2.1

---

- [`uSockets`](https://github.com/uNetworking/uSockets)
- Apache 2.0

---

- [`zlib-cloudflare`](https://github.com/cloudflare/zlib)
- zlib

---

- [`c-ares`](https://github.com/c-ares/c-ares)
- MIT licensed

---

- [`libicu`](https://github.com/unicode-org/icu) 72
- [license here](https://github.com/unicode-org/icu/blob/main/icu4c/LICENSE)

---

- [`libbase64`](https://github.com/aklomp/base64/blob/master/LICENSE)
- BSD 2-Clause

---

- A fork of [`uWebsockets`](https://github.com/jarred-sumner/uwebsockets)
- Apache 2.0 licensed

---

- Parts of Tigerbeetle's IO code https://github.com/tigerbeetle/tigerbeetle/blob/532c8b70b9142c17e07737ab6d3da68d7500cbca/src/io/windows.zig#L1
- Apache 2.0 licensed

{% /table %}

## Polyfills

For compatibility reasons, the following packages are embedded into Bun's binary and injected if imported.

{% table %}

- Package
- License

---

- [`assert`](https://npmjs.com/package/assert)
- MIT

---

- [`browserify-zlib`](https://npmjs.com/package/browserify-zlib)
- MIT

---

- [`buffer`](https://npmjs.com/package/buffer)
- MIT

---

- [`constants-browserify`](https://npmjs.com/package/constants-browserify)
- MIT

---

- [`crypto-browserify`](https://npmjs.com/package/crypto-browserify)
- MIT

---

- [`domain-browser`](https://npmjs.com/package/domain-browser)
- MIT

---

- [`events`](https://npmjs.com/package/events)
- MIT

---

- [`https-browserify`](https://npmjs.com/package/https-browserify)
- MIT

---

- [`os-browserify`](https://npmjs.com/package/os-browserify)
- MIT

---

- [`path-browserify`](https://npmjs.com/package/path-browserify)
- MIT

---

- [`process`](https://npmjs.com/package/process)
- MIT

---

- [`punycode`](https://npmjs.com/package/punycode)
- MIT

---

- [`querystring-es3`](https://npmjs.com/package/querystring-es3)
- MIT

---

- [`stream-browserify`](https://npmjs.com/package/stream-browserify)
- MIT

---

- [`stream-http`](https://npmjs.com/package/stream-http)
- MIT

---

- [`string_decoder`](https://npmjs.com/package/string_decoder)
- MIT

---

- [`timers-browserify`](https://npmjs.com/package/timers-browserify)
- MIT

---

- [`tty-browserify`](https://npmjs.com/package/tty-browserify)
- MIT

---

- [`url`](https://npmjs.com/package/url)
- MIT

---

- [`util`](https://npmjs.com/package/util)
- MIT

---

- [`vm-browserify`](https://npmjs.com/package/vm-browserify)
- MIT

{% /table %}

## Additional credits

- Bun's JS transpiler, CSS lexer, and Node.js module resolver source code is a Zig port of [@evanw](https://github.com/evanw)’s [esbuild](https://github.com/evanw/esbuild) project.
- Credit to [@kipply](https://github.com/kipply) for the name "Bun"!