Legal help needed


I’m not quite sure if it’s the right place to ask this.
I’m a developer for quite some time now on UE and i’ve started CPP some time ago now. I have a project to convert UMAPs to VMF (valve map files) for the game Portal 2. That’s to make modding/mapping easier using UE which is fairly more intuitive to use rather than the modding tool provided by the developers to map the game.
My question is, is it legal to do this? Portal 2’s developers provided themselves an editor, i’m just making an alternative option, is that legal?

Thanks !

Unless you’ve contacted both parties about this issue and they’ve both greenlit your project, it’s usual better to err on the side of caution with projects like these