Protocol Buffers Package specifier protocol buffer guide Google Protocol Buffer Language Google's Language Guide define your messages in .proto files Protocol Buffers Package specifier developers.google.com/protocol-buffers/docs/proto#other developers.google.com extensions definition of the PB programming language proprietary language Google Protocol Buffers Language Guide Google Protocol Buffers Language Guide according to the documentation Language Guide extensions the documentation Language Guide Google Protocol Buffers Language Guide nice docs option developers.google.com Google Protocol Buffers Language Guide language guide ProtoBufs according to the documentation language guide