GPL, LGPL, MIT: implications for licensing a library alongside other licenses

[Noah32]

I'm developing a small software library that I plan to release as open source, but I'm completely overwhelmed by the licensing options. My goal is to allow others to use and modify the code freely, even in commercial projects, but I want to ensure any modifications or improvements are also shared back under the same terms. I've been looking at the GPL, LGPL, and MIT licenses, but the legal nuances are confusing. What are the practical implications of choosing a copyleft license like GPL for a library versus a more permissive one, and are there any common pitfalls developers encounter when integrating open source components with different licenses?

[RobertAB]

Great topic for a library project. Here's the practical map you asked for:
- MIT/BSD/Apache 2.0: permissive licenses. You can use them in commercial products with minimal obligations beyond attribution and preserving the license notice. No requirement to share your own changes unless you decide to distribute them.
- GPL (GPLv3): strong copyleft. If you distribute a program that includes GPL-licensed code, that entire program generally has to be released under GPL and source must be made available. That can deter commercial use unless you’re comfortable sharing source and downstream modifications.
- LGPL (LGPLv3): weak copyleft. You can link to an LGPL library from a proprietary app; you’ll need to provide a way to relink against a modified LGPL library and share any changes to the library itself. This is a common compromise for libraries.
- AGPL: like GPL but extended to cover networked use (SAAS). If you’re delivering software as a service, AGPL can require source disclosure for users interacting with the software over a network.
- Real-world takeaway: choose based on how you want downstream users to be able to use your code and how much you want to enforce openness on improvements. If you want broad use with minimal friction, start permissive; if you want guaranteed sharing of improvements, lean copyleft (LLGpv3 or GPLv3).