[catwell]

I +1 that. I have working experience with MessagePack and I can confirm it works for the following use cases:

* RPC communication between servers where binary data is exchanged and its structure is not always the same (ie. difficult to use something that requires an IDL).

* Serialization and storage of objects that will be sent over the network (note: you can batch MessagePack objects just by concatenating them).

* Communication between a server and a native mobile application. Native applications live in a binary world whereas Web applications live in a text-based world where JSON is better.

The human readability argument is poor: the JSON that is sent over a network is not usually human readable, so you would use a prettyfier to read it anyway. Moreover a MessagePack message is standalone / self-describing, ie. you don't need an IDL description to read it. So in both case, reading the message is just adding another block to a pipeline...