AGPL-3.0

Whoever writes a program holds copyright over it and may determine what others are allowed to do with it. This permission is laid out in a text called a license. AGPL-3.0 is one such license, and a very generous one at that, with one clear condition. It allows anyone to use, copy, modify, and redistribute the program. In return, it requires that the modified version be disclosed again under the same terms. The full name is GNU Affero General Public License, Version 3; the number denotes the current version from 2007.

The gap Affero was meant to close

Older licenses in this family tied the disclosure obligation to distributing the software to others. That fit well in an era when programs were sold on CDs. Today, software often runs on someone else’s servers, and users access it only through a browser. In that case, the provider never hands out the program, yet still profits from it.

This gap is often called the ASP loophole, after the English term for providers of software as an online service. AGPL-3.0 closes it with a single additional clause. As soon as users work with the program over a network, they must be offered the program source code — even if no one downloads a file.

For the AI industry, this has become a concrete issue. Many tools for databases, search systems, or model deployment are released under AGPL-3.0. Large providers often avoid such components in their own products. Some companies deliberately use this license for that very reason: they don’t want competitors to quietly build the code into closed services.

What copyleft actually requires

The principle behind this is called copyleft, a play on words with copyright. It means: the freedoms stay attached to the software. Whoever modifies it and passes it on must pass along the same freedoms. So you may not take it, improve it, and then lock the result away.

In practice, this means three things. First, the complete program source code of one’s own version must be made available, not just an excerpt. Second, it must be released under AGPL-3.0, not under a stricter condition. Third, the names of the original authors and the license notices must be preserved.

A common misconception: AGPL-3.0 forbids commercial use. That’s false. You are allowed to make money with AGPL software, even as a paid online service. You just may not keep your own modifications secret. Equally false is the concern that merely using a service obligates you to anything. The obligations fall on the operator, not on a website’s visitor.

AGPL compared to MIT and GPL

On platforms for program source code like GitHub, every project lists its license. Alongside AGPL-3.0, you’ll mainly encounter two others there. The MIT license permits almost everything and demands practically nothing in return. GPL-3.0 requires disclosure, but only upon genuine distribution of the program. AGPL-3.0 is the strictest of the three, because it also covers online services.

Well-known examples include the cloud software Nextcloud, the charting tool Grafana in earlier versions, and the vector database Milvus. AGPL also regularly comes up in reports about license changes. Companies switch, for instance, from an open license to a stricter one when cloud giants resell their product.

If you’re programming yourself, the question is simple to ask. Should your code be allowed to end up anywhere, even in closed products? Then MIT fits. Should every improvement become public again, even in server operation? Then AGPL-3.0 fits. For commercial projects, it pays to carefully check beforehand which third-party components you’re incorporating.