Developer file created in Google's Protocol Buffer format, a data serialization format used for exchanging data; specifies one or more "messages" as logical records, each of which contains name-value pairs (e.g., a Person message may have an ID, name, and address); designed as an alternative to XML for data exchange.

Once a protocol buffer's schema has been specified, you can use the Google Java, C++, or Python protocol buffer libraries ("protobuf") to auto-generate source code. Once generated, the source code can be used in your program for creating structured data and reading and writing it to input and output streams. Protocol buffers are used for serializing objects from Java, C++, or Python programs. This allows data to be encoded in a common format and exchanged between applications written in the three languages. NOTE: Protocol buffers are used by almost all of Google's in-house file formats and RPC protocols.