IANAL, but I don't think your employer could make an "IP claim" on work that wasn't at least created using their time and resources, particularly not under a FOSS license.This is something you should be discussing with your employer, since it depends on company policy.
to me, since the code have been produced before the contract, they don't hold the IP. I'm not a lawyer, I can be wrong.
Is your idea to use the tool worth the cans of worms use might open up?
If it might be, talk to your boss about it and your terms of employment concerns.
But in the end all IP claims are only as good as your wherewithal to lawyer up divided by your opponents’ wherewithal to do likewise.
Good business/professional/personal relationships are much much better than lawyers. And cheaper too.
Good luck.
> Would my current company have an IP claim on my project if I use it at work?
Not because of that, no. However -- depending on the terms of your employment -- your contract may have one of those nasty clauses that give them IP rights to anything you develop during your employment. If that's the case, they may have a claim based on that and that claim would apply whether or not the software was used at work. Those clauses are the first things I look for and negotiate away when getting hired.
My advice is to talk to an attorney about all this. A short consultation shouldn't cost a fortune.