The MIT software license is one of the most permissive open-source licenses in wide use: you can use, copy, modify, merge, publish, distribute, sublicense, and sell the software, with essentially one obligation — keep the copyright and license notice intact. That simplicity is exactly why it dominates the JavaScript ecosystem and shows up in a large share of packages your applications depend on. But "permissive" does not mean "no obligations," and license compliance at scale is where the simplicity gets deceptive.
What the MIT license actually says
The full license is a few sentences. Its operative grant reads: permission is granted, free of charge, to any person obtaining a copy of the software, to deal in it without restriction. The only real condition:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
The remainder is a warranty disclaimer written in capital letters, stating the software is provided "as is" and the authors are not liable for anything.
So the compliance requirement is genuinely narrow: when you redistribute MIT-licensed code, include its copyright notice and the license text. That is it. There is no requirement to open your own source, no copyleft, no patent clause.
The one obligation people miss
Because the requirement is so light, teams forget it entirely. The failure mode is shipping a compiled binary, a bundled JavaScript file, or a Docker image that includes MIT-licensed code without carrying the accompanying notices. Technically, that is a license violation, even though nobody is likely to sue over a missing attribution line.
The fix is a standard part of a release pipeline: generate a THIRD_PARTY_NOTICES or LICENSES file that aggregates the notices of everything you bundle. Most build ecosystems have a tool for this — for example, in Node:
npx license-checker --production --out licenses.txt
This walks your dependency tree and collects each package's license and copyright, which you then include in your distribution.
MIT versus Apache 2.0 versus GPL
The MIT license sits at the permissive end of the spectrum. A quick orientation:
- MIT / BSD: permissive, attribution only, no patent grant.
- Apache 2.0: permissive, attribution, plus an explicit patent license and a notice for modified files. Preferred when patent protection matters.
- GPL / LGPL / AGPL: copyleft. Distributing derivative works can obligate you to release source under the same terms. The AGPL extends this to network use.
The practical risk is not MIT itself — it is mixing MIT code with strong copyleft code and not noticing. If a GPL-licensed dependency slips into a product you distribute as proprietary, that is a real legal exposure, not a missing-attribution nitpick. Our full software licenses guide walks the whole spectrum in more depth.
Tracking licenses across a real dependency tree
A modern application has hundreds to thousands of transitive dependencies, each with its own license. Doing this by hand is not feasible. This is where a software bill of materials (SBOM) earns its keep: it enumerates every component and its license, so you can enforce policy automatically.
A practical policy looks like: allow MIT, BSD, Apache 2.0, and ISC by default; flag anything copyleft for review; block unknown or missing licenses. An SCA tool that generates an SBOM and evaluates a license policy on every build turns "hope nothing bad got in" into a gate that fails the pipeline when a disallowed license appears.
When "MIT" is not quite MIT
Watch for variants. Some packages declare "MIT" but ship a modified text, or dual-license under "MIT OR Apache-2.0." SPDX identifiers help here: standardize on the SPDX expression (MIT, MIT-0, MIT OR Apache-2.0) rather than free-text license fields, so your tooling parses them consistently. The MIT-0 variant, notably, drops even the attribution requirement.
FAQ
Can I use MIT-licensed code in a commercial closed-source product?
Yes. The MIT license explicitly permits commercial use and does not require you to open your own source. You only need to include the original copyright and license notice in your distribution.
Do I have to publish my changes to MIT-licensed code?
No. Unlike copyleft licenses such as the GPL, the MIT license imposes no obligation to share modifications. You can modify the code and keep your changes private.
What is the difference between the MIT and Apache 2.0 licenses?
Both are permissive, but Apache 2.0 adds an explicit patent grant and requires noting modified files. MIT is shorter and has no patent clause. Choose Apache 2.0 when patent protection is a concern.
How do I stay compliant with MIT licenses across many dependencies?
Generate a software bill of materials that lists every component and its license, and enforce a license policy in CI. This scales attribution and copyleft-detection far beyond manual review.