For Cap'n Proto to help, you have to switch from using JSON format to using Cap'n Proto format, which is indeed a lot more than just one function call. But it s

For Cap'n Proto to help, you have to switch from using JSON format to using Cap'n Proto format, which is indeed a lot more than just one function call. But it should be orders of magnitude faster than JSON. So if profiles show you're spending a lot of time in JSON handling, then, yes, it could help. Right now, Cap'n Proto makes the most sense for server <-> server communications, e.g. between a front-end and a back-end. In the future I hope to have a production-ready implementation in Javascript, which would allow you to use Cap'n Proto all the way up the stack.