Eh... I'd actually argue that Protobuf's big advantage is all the languages it supports that Cap'n Proto doesn't. If you're using C++ exclusively, I'd argue Ca

Eh... I'd actually argue that Protobuf's big advantage is all the languages it supports that Cap'n Proto doesn't. If you're using C++ exclusively, I'd argue Cap'n Proto beats Protobuf. That "army of engineers" isn't necessarily the advantage you think it is -- rather than forcing Protobuf to be the best it can be, I would argue they forced Protobuf to get stuck with early design decisions that no one thinks were ideal (e.g. varint encoding), because it's too hard to change once you have a lot of users. Battle-testing is great, but you could argue that Cap'n Proto benefited more from Protobuf's battle-testing than Protobuf itself did, since Cap'n Proto was designed from scratch with those lessons already learned. On the other hand, if you need to support a broad set of languages, Protobuf is more likely to meet your needs. This is where the army of engineers and Google backing is helpful -- in building out support for a wide variety of languages and platforms.