Navigating Open Source Licenses: How to Use Free Software Commercially Without Getting Sued
A plain-english guide to MIT, Apache, and GPL licenses. We explain exactly which licenses are safe for startups and commercial products, and which to avoid.
We are developers, not lawyers. This is an educational guide for informational purposes only. When in doubt, always consult qualified legal counsel.
The "Viral" Fear of Open Source
Startups love free software but fear the "Copyleft" effect—the idea that using one piece of open-source code will force you to open-source your entire proprietary product. The truth is nuanced, but understanding three main categories of licenses will save you 99% of headaches.
Category 1: The Green Light (Permissive)
These licenses basically say "Do whatever you want, just don't sue us." They are overwhelmingly safe for commercial use, SaaS, and internal tools.
MIT License
The Gist: You can use, copy, modify, merge, publish, distribute, sublicense, and sell copies of the software.
Requirement: Include the original copyright notice in your software (usually in a text file credits or "About" screen).
Commercial Use? YES.
Apache 2.0 License
The Gist: Similar to MIT but legal-hardened. It includes a specific clause about patent rights. It protects you from the contributor suing you for patent infringement later.
Commercial Use? YES. Preferred by large enterprises (Google, Android, etc.).
BSD Licenses (2-Clause / 3-Clause)
The Gist: Very similar to MIT. The 3-clause version includes a "non-endorsement" clause, meaning you can't use the name of the project to promote your product without permission.
Commercial Use? YES.
Category 2: The Yellow Light (Weak Copyleft)
Mozilla Public License (MPL) & LGPL
These are often used for libraries components.
The Rule: If you use the library "as is" (linking to it), you can keep your own code private. However, if you modify the library file itself, you must share those specific modifications back to the community.
Commercial Use? YES, but be careful not to modify the core files unless you plan to share.
Category 3: The Red Light (Strong Copyleft)
GPL v2 / v3
The Gist: If you distribute software that relies on GPL code (linked statically or dynamically), your entire software must likely be released under the GPL. It is "viral" - it infects your proprietary code.
Commercial Use? Tricky.
You can sell it, but you must give the customer the source code. This destroys most SaaS business models that rely on proprietary code secrets.
AGPL (Affero GPL)
The Gist: Designed to close the "SaaS Loophole". Even if you don't distribute the software (just run it on a server), you must share source code if users interact with it over a network.
Commercial Use? HIGH RISK.
Avoid unless using as a standalone service that you do not modify.
Deep Dive: Dual Licensing
You might see tools (like Qt or MySQL) offering "Dual Licensing". This means they offer the software under GPL (for free open source projects) AND under a commercial license (paid) for proprietary projects.
If you are building a proprietary SaaS and want to use a GPL component, you often can—you just have to pay the company for the Commercial License exception. This is a valid business model.
How Project Free To Use Helps
In our Open Source Directory, we explicitly verify license types. We favor MIT and Apache 2.0 projects because we know our users are builders who want to ship products, not read legal briefs.
Quick Decision Tree
- Building a website? → MIT / Apache / BSD are safe.
- Modifying a library? → MPL / LGPL might require sharing changes.
- Building proprietary SaaS? → Avoid GPL / AGPL unless you speak to a lawyer.