How to export a texture atlas

I am creating a texture in Asperite that consists of six elements of an object, but there are three different variants. Now I want to export the bounding boxes of these objects. So basically 12 different bounding boxes to import in my game – I don’t want to hardcode it. I wish there was an option that lets me label objects and exports a simple text file with the bounding boxes, which my game loads.

How do I accomplish this? I tried putting all objects in the same layer and tried to export something with the Export Sprite Sheet option, but nothing happened. Obviously I need to specify the bounding boxes myself (probably with single layers?), but I am unsure if I can do this with Aseprite at all.

The easiest way is probably to make each variant its own set of frames grouped via tags, and then use the tags to let your engine know which thing is which.