The files in format_declearations are KaiTai (https://kaitai.io/) files. To convert the file parsing structure in those files to python file, you need to compile them. You can do this by running them though the kaitai compiler: kaitai-struct-compiler -t python ./format_declarations/* It will output the python files to the folder you are running the command from The compare_data.py is sanity check helper that can parse and compare two python data structures to each other. It is used to see if two loaded cpj files or chunks are the same or if they differ.