Which licences are acceptable for Javascript libraries embedded in SE sites?

Question

Several SE sites have certain custom Javascript libraries that provide functionality that specific to those sites. For example, the Mathematics sites as well as many Science sites use MathJax to allow users to enter mathematical formulas. There are others as well like components for sketching UIs and circuit design.

These are almost always external projects and not written by SE, so obviously licence issues play some part here. There is a certain functionality that I think would be very useful on some sites and wanted to look around for some existing implementations. I'd like to focus on one or two good candidates and take a closer look, and I'd like to avoid investigating an option that can't be used due to licence issues.

Which of the common open-source licences are acceptable for SE and can be included on SE sites without problems? The major candidates would be GPL, LGPL, AGPL and other copyleft licences where I'm not sure if they would be acceptable or not.

Answer 1

I am not a lawyer and I don't know what our license restrictions are off the top of my head, but I think you might be overthinking this a bit. The roadblocks to us using a third-party library are often less license-based and more concerned with performance, need, implementation, etc.

Besides, if there's a feature that'd benefit our sites, we have no particular qualms about implementing it (assuming we all agree that it's needed, etc.) without needing to pull in a 3rd-party plugin. Alternatively, we can contact the developers to work out a special licensing arrangement. There are various approaches we could take there.

My advice would be to just do your research and present your ideas on meta before you worry about the minutiae of licensing, etc. So long as it's not something super restrictive (like requiring us to open-source our Q&A code), it's unlikely to be a huge deal.