Proto3 defines typed messages and stable field numbers for shared payloads

This reference covers the proto3 revision of the Protocol Buffers language: how to structure data in .proto files and generate data access classes. It points elsewhere for Protobuf Editions and proto2. The worked example defines a SearchRequest message with a string query and int32 page_number and results_per_page fields under syntax = "proto3".

Each field has a name, a type, and a number in the allowed range stated in the extract. Types may be scalars, enumerations, or other message types. The syntax or edition declaration must be the first non-empty, non-comment line; without it the compiler assumes proto2. The guide is framed as reference material alongside language-specific tutorials.

Cross-system contracts depend on exactly this kind of explicit shape: named fields, types, and stable numbers that serializers share. For data and AI pipelines exchanging structured payloads, proto3 messages are a governed schema surface rather than ad hoc JSON. Field numbers and message composition are the shared meaning agents and services must agree on before validation or transformation.