MessagePack is an efficient binary serialization format. It lets you exchange data among multiple languages like JSON. But it’s faster and smaller. Small integers are encoded into a single byte, and typical short strings require only one extra byte in addition to the strings themselves.

Source: MessagePack: It’s like JSON. but fast and small.

Much faster. Also supported in Redis:

Redis scripting has support for MessagePack because it is a fast and compact serialization format with a simple to implement specification. I liked it so much that I implemented a MessagePack C extension for Lua just to include it into Redis.

— Salvatore Sanfilippo, creator of Redis