Cool, v023 works with my sprites and tests! Thank you for the update!
> Could you please tell, what game engine do you use?
I'm writing a custom engine for a 2D game in Odinlang with SDL and OpenGL.
I've also written my own sprite sheet generator, which has a different use case than yours and way less features: CLI only and all sprites must have the same size.
When looking for alternatives before writing my own, I've found mostly super bloated web thingies, which I don't like. Your app is nice and small, meant for a single thing -> pretty much what I was looking for!