It depends what you mean by zero-copy. It can't be traversed without parsing the structure, but strings and binary blobs can be used in-place without copying. (

It depends what you mean by zero-copy. It can't be traversed without parsing the structure, but strings and binary blobs can be used in-place without copying. (This is also possible with JSON even, for example with RapidJSON's in-situ parser.) This has worse performance for decoding, but far better performance for encoding. Encoding any traversible format is guaranteed to be expensive because you have to encode it inside-out, calculating the nested sizes of everything as you go. For messages that are only encoded once and read once, for example network messages, a format that is traversible in-place is a poor choice.