GNU General Public License
jee-pee-ELL
A copyleft open source license that requires derivative works to also be distributed under the GPL.
The GPL is the most well-known copyleft license. Its central rule: if you distribute software that includes GPL-licensed code, you must make the entire combined work's source code available under the GPL. This is the "viral" property that makes corporate legal teams nervous.
The GPL was created by Richard Stallman and the Free Software Foundation. Its philosophy is that software freedom should propagate. If you benefit from open source code, your modifications should benefit others too. Linux, GCC, WordPress, and thousands of other projects use the GPL.
For SaaS companies, the GPL has a notable gap. The license triggers on distribution, and serving software over the web is not distribution. A company can modify GPL code, run it on their servers, and never release the changes. The AGPL (Affero GPL) closes this gap by requiring source disclosure for network use. The BSL and SSPL represent alternative approaches to protecting commercial interests.
Examples
A company wants to include a GPL library in their proprietary product.
The legal team raises a red flag. If the library is linked into the product and the product is distributed, the entire product may need to be released under the GPL. They look for an MIT or Apache alternative.
A developer releases a project under GPLv3.
A company forks the project and adds features. When they distribute the modified version, they must release the full source code under GPLv3, including their additions.
A SaaS company runs modified GPL software on their servers.
Because they are not distributing the software (users access it over the web), the GPL does not require them to release the source. The AGPL would, but the original project uses the GPL.
Frequently asked questions
Can GPL-licensed code be used commercially?
Yes, but with conditions. You can sell GPL software. However, anyone you distribute it to must also receive the source code and the right to modify and redistribute it under the GPL.
What is the difference between GPLv2 and GPLv3?
GPLv3 adds protections against patent claims (similar to Apache) and anti-tivoization clauses that prevent hardware manufacturers from locking down GPL software. Linux uses GPLv2; many newer projects use GPLv3.
Related terms
A permissive open source license that allows anyone to use, modify, and distribute the software with minimal restrictions.
A permissive open source license that includes an explicit patent grant and requires attribution for modifications.
The practice of tracking and fulfilling the legal obligations of all open source software used in a product.
A source-available license that restricts commercial use for a set period before converting to a fully open source license.
Want the complete playbook?
Picks and Shovels is the definitive guide to developer marketing. Amazon #1 bestseller with practical strategies from 30 years of marketing to developers.