Cap'n Proto was created by the former maintainer of Google's popular Protocol Buffers framework (Kenton Varda) and was designed to avoid some of its perceived shortcomings.

The Cap'n Proto interface schema uses a C-like syntax and supports common primitives data types (booleans, integers, floats, etc.

[3] Values in Cap'n Proto messages are represented in binary, as opposed to text encoding used by "human-readable" formats such as JSON or XML.

[4] When the in-memory and wire-protocol representations match, Cap'n Proto can avoid copying and encoding data when creating or reading a message and instead point to the location of the value in memory.

[15] The Cap'n Proto RPC standard has a rich capability security model based on the CapTP protocol used by the E programming language.