MessagePack lets you use integers for keys, so you can use enums or integer constants in the code instead of strings. There are good reasons to use MessagePack

MessagePack lets you use integers for keys, so you can use enums or integer constants in the code instead of strings. There are good reasons to use MessagePack over Protobuf even if you don't need readability, such as easier integration into buildsystems and better support for embedded platforms.