It's like JSON. but fast and small.
It looks cool, but be very careful about using it (in a browser, at least). Browsers have super-fast JSON parsers and parsing msgpack is much, much slower than parsing good old JSON.<p>This great comment (from 201 days ago) is exactly about this issue:<p><a href="http://news.ycombinator.com/item?id=4091051" rel="nofollow">http://news.ycombinator.com/item?id=4091051</a><p>I quote a bit of it here:<p><pre><code>    JSON size: 386kb
    MsgPack size: 332kb
    Difference: -14%

    Encoding with JSON.stringify 4 ms
    Encoding with msgpack.pack 73 ms
    Difference: 18.25x slower

    Decoding with JSON.parse 4 ms
    Decoding with msgpack.unpack 13 ms 
    Difference: 3.25x slower

</code></pre>
and also this comment: <a href="http://news.ycombinator.com/item?id=4093077" rel="nofollow">http://news.ycombinator.com/item?id=4093077</a><p><pre><code>   MessagePack is not smaller than gzip'd JSON
   MessagePack is not faster than JSON when a browser is involved
   MessagePack is not human readable
   MessagePack has issues with UTF-8
   Small packets also have significant TCP/IP overhead</code></pre>