Zerorpc (http://github.com/dotcloud/zerorpc-python) uses msgpack as its primary serialization format. Among other things it is significantly more efficient for floating point data. At dotCloud we use it to move many millions of system metrics per day, so it adds up. Also worth noting: msgpack maps perfectly to json, so there's nothing keeping you from translating it to json on its way to the browser, where json is indeed a better fit. In practice this doesn't affect performance since you typically need to parse and alter the message at the browser boundary anyway, for some sort of access control.