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 clone https://github.com/oven-sh/WebKit vendor/WebKit
• bun sync-webkit-source (checks out the version pinned in WEBKIT_VERSION in scripts/build/deps/webkit.ts)
• bun run build:local

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
ls-hpack	MIT
ls-qpack	MIT
lsquic	MIT (portions derived from Chromium proto-quic, 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-ng	zlib
c-ares	MIT licensed
libicu 78	license here
libbase64	BSD 2-Clause
libuv (on Windows)	MIT
libdeflate	MIT
libjpeg-turbo	BSD 3-Clause / IJG / zlib
libspng	BSD 2-Clause
libwebp	BSD 3-Clause
highway	Apache 2.0
uucode	MIT
A fork of uWebsockets	Apache 2.0 licensed
Parts of Tigerbeetle's IO code	Apache 2.0 licensed
__cxa_thread_atexit fallback from LLVM libc++abi	Apache 2.0 with LLVM exception
The type checker behind bun check and the parser it shares with bun lint and bun fmt are ports of typescript-go. They use TypeScript's diagnostic messages and lib.*.d.ts files	Apache 2.0
bun lint ports large parts of ESLint: code path analysis, rule helpers such as ast-utils.js, config and comment handling, and many rules. The ESLint rules in bun lint use ESLint's rule names, options, option schemas, messages and descriptions. The eslint:recommended and eslint:all presets are ESLint's. Parts of main.js in src/lint/js_plugin/worker are copied from ESLint, and parts of LintReport.cpp, LintSourceCode.cpp and LintTokens.cpp in src/jsc/bindings are ported from it	MIT
bun lint does the same with the rules of typescript-eslint. It also ports type-utils and the plugin's util helpers, and uses its presets, the error messages of typescript-estree and the lib globals of scope-manager	MIT
Selectors in bun lint are a port of esquery	BSD 3-Clause
bun lint has ports of @eslint-community/regexpp, @eslint-community/eslint-utils, levn and natural-compare, and of parts of ts-api-utils and @eslint/eslintrc	MIT
bun lint uses the error messages of ajv, acorn and optionator, and the lists in globals and is-core-module	MIT
bun lint uses the error messages of espree	BSD 2-Clause
bun lint uses the JSON.parse error messages of V8	BSD 3-Clause
bun lint has ports of parts of @eslint/plugin-kit, @eslint/config-array, @eslint/config-helpers and @eslint/compat	Apache 2.0
bun lint and bun fmt have a port of the pattern-to-regular-expression table of ignore	MIT
bun lint and bun fmt have ports of is-glob and is-extglob	MIT
bun lint and bun fmt have a port of glob-parent	ISC
The react-hooks, import, n, react and prettier rules in bun lint are ports of the rules in eslint-plugin-react-hooks, eslint-plugin-import, eslint-plugin-n, eslint-plugin-es-x, eslint-plugin-react and eslint-plugin-prettier, with the same rule names, options and messages. They include the Node.js version tables of eslint-plugin-n and a few functions from jsx-ast-utils and prettier-linter-helpers	MIT
The text diff used by bun test and the prettier/prettier rule has parts of diff-match-patch and of fast-diff, which is derived from it	Apache 2.0
The unicorn, oxc, react-perf, jsx-a11y, nextjs, promise, node, jest and vitest rules in bun lint are ports of the rules in oxlint, with its messages and help text. With an oxlint config, the other rules use the messages of oxlint and tsgolint too. bun lint also ports parts of oxc_jsdoc and oxc_react_compiler	MIT
oxlint ported those rules from eslint-plugin-unicorn, eslint-plugin-react-perf, eslint-plugin-jsx-a11y, @next/eslint-plugin-next, eslint-plugin-n, eslint-plugin-jest and @vitest/eslint-plugin. Their rule names, options and some of their messages are in bun lint	MIT
oxlint ported its promise rules from eslint-plugin-promise	ISC
The ARIA tables of the jsx-a11y rules come from aria-query by way of oxlint	Apache 2.0
bun fmt is a port of Prettier: its printers for CSS, SCSS, Less, HTML, Vue, Angular, Markdown, YAML, GraphQL and Handlebars, its document printer, its handling of options, pragmas, ranges, cursor offsets and embedded code, and the HTML tables it is built with	MIT
The JavaScript and TypeScript printer of bun fmt, its JSDoc formatting and its oxfmt-style import sorting are a port of oxc_formatter, which is a port of the Biome formatter. The intermediate representation and its printer come from Biome by way of oxc_formatter_core	MIT
bun fmt has ports of the parsers in postcss, postcss-scss, postcss-less, postcss-selector-parser, postcss-media-query-parser, postcss-values-parser, angular-html-parser, graphql-js, @glimmer/syntax, simple-html-tokenizer and @angular/compiler, and of parts of yaml-unist-parser and angular-estree-parser	MIT
bun fmt also has a port of @handlebars/parser and of one file of yaml	ISC
Import sorting in bun fmt has ports of @trivago/prettier-plugin-sort-imports and @ianvs/prettier-plugin-sort-imports, and of organizeImports.ts in TypeScript	Apache 2.0
bun fmt has ports of jest-docblock and the crates sort-package-json and oxc-toml (a fork of taplo), and of parts of @babel/generator, micromark and editorconfig-without-wasm. Its character width tables are generated from emoji-regex, get-east-asian-width and narrow-emojis	MIT
Tailwind class sorting in bun fmt is a port of parts of prettier-plugin-tailwindcss	MIT
Svelte formatting in bun fmt is a port of prettier-plugin-svelte and of the template parser of Svelte	MIT

The tests in test/cli/lint/conformance and test/cli/format include test cases from ESLint, typescript-eslint, the ESLint plugins above, oxc, tsgolint, Prettier and the two import sorting plugins. They are not part of the bun binary. Their licenses are next to them.

Polyfills

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

Package	License
acorn	MIT
acorn-walk	MIT
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 port of @evanw’s esbuild project.
• Credit to @kipply for the name "Bun"!