At this point, just don't design file format. Use flatbuffers. 1. It has good forward / backward compatibility stories; 2. Schema is your file format document

At this point, just don't design file format. Use flatbuffers. 1. It has good forward / backward compatibility stories; 2. Schema is your file format documentation; 3. Don't need to decode every parts; 4. Can skip for unknowns (if you use union type); 5. Many language bindings. The only downside, and this is a big one: validate a flatbuffers payload method doesn't have nearly as much language coverage as the encode / decode methods. (i.e. C++ has it, but a lot of other languages don't have validate method implemented). Case study - Apache Arrow uses flatbuffers to persist its metadata: https://github.com/apache/arrow/tree/master/format https://github.com/apache/arrow/tree/master/format