Protocol Buffers (Protobuf)
Protocol Buffers, or Protobuf, is a free and Open Source Cross-Platform data format used to serialize structured data. It is useful in developing programs to communicate with each other over a Network or for storing data. Protobuf is more compact and Performant than REST API.
Proto Files
Protocol Buffers comes with its own DSL to describe the structure of data, called Proto files.
There are two Proto versions: proto2 and proto3. These two versions are wire-compatible, but the DSLs are only compatible to some extend.
Code Generation
Protobuf also comes with its own source code generator (Protoc) which can generate source code in several languages from Proto files, that can subsequently be used to serialize, deserialize, and stream the structured data.
The source code generator also comes with an API that can be used to create your own code generator. The API provides an interface to every aspect of the DSL up to the comments. There is basically no limit to how this API can be used. One could: