I am forced to use some proprietary software at work. The software lets users export custom functionalities. You can then share these to other users. I have made some that are pretty simple, but greatly enhance the use of the application using its native tooling.

I'd like to share mine under some sort of open source licence rather than being ambiguous. Mostly to spread awareness of the concept of open source which is at approximately 0% right now.

What are the considerations here? Can I use the GPL or is it inherently out of compliance since you need a proprietary software to run it?

The employer doesn't claim any intellectual property rights over my work product. I'm not able to find anywhere that the proprietary vendor does either. But I haven't gone through everything with a fine tooth comb. What language would I be looking for?

Advice appreciated. Obviously it can only be general as many details are missing. I just don't understand the details of licences very well.