A structure file represents a structure and is denoted by the .rcst suffix.
File Structure[]
Structure files are zips containing multiple files, each representing a different part of the structure data.
structure.json[]
Contains all the structure's generation metadata. Can loosely be defined as the file representation of the Structure Configuration GUI.
You can look up the source for more specific data about the file format.
worldData.nbt[]
Contains the actual structure data itself. Can be compared to a schematic file: Although it is saved differently, it contains similar types of data.
You can look up the source for more specific data about the file format. Remember that IvToolkit is Apache 2.0 distributed, so if you want to, you can copy the source to read these files yourself.