LICENSE.md

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:

Library	License
boringssl	several licenses
brotli	MIT
libarchive	several licenses
lol-html	BSD 3-Clause
mimalloc	MIT
picohttp	dual-licensed under the Perl License or the MIT License
zstd	dual-licensed under the BSD License or GPLv2 license
simdutf	Apache 2.0
tinycc	LGPL v2.1
uSockets	Apache 2.0
zlib-cloudflare	zlib
c-ares	MIT licensed
libicu 72	license here
libbase64	BSD 2-Clause
A fork of uWebsockets	Apache 2.0 licensed
Parts of Tigerbeetle's IO code	Apache 2.0 licensed

Polyfills

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

Package	License
assert	MIT
browserify-zlib	MIT
buffer	MIT
constants-browserify	MIT
crypto-browserify	MIT
domain-browser	MIT
events	MIT
https-browserify	MIT
os-browserify	MIT
path-browserify	MIT
process	MIT
punycode	MIT
querystring-es3	MIT
stream-browserify	MIT
stream-http	MIT
string_decoder	MIT
timers-browserify	MIT
tty-browserify	MIT
url	MIT
util	MIT
vm-browserify	MIT

Additional credits

• Bun's JS transpiler, CSS lexer, and Node.js module resolver source code is a Zig port of @evanw’s esbuild project.
• Credit to @kipply for the name "Bun"!