If you need a format that can transport byte arrays unmodified (image data, etc), msgpack (or protos or whatever) is much better than JSON since you don't have

If you need a format that can transport byte arrays unmodified (image data, etc), msgpack (or protos or whatever) is much better than JSON since you don't have to base64 encode or escape the data. It also supports non-string keys which can be convenient.