Protocol Buffers
Protobuf is the wire format for gRPC and many high-performance internal APIs. Schemas are also used for event/message contracts in Kafka/pubsub systems.
What It Defines
Google's language-neutral, platform-neutral binary serialization format. Defines `.proto` schema files, data types, field numbers, and binary encoding rules. More compact than JSON; requires schema for decoding.
Canonical (Normative)
Convenient (Practical)
gRPC is an open-source RPC framework originally developed at Google. It uses Protocol Buffers (protobuf) as its IDL and wire format, and HTTP/2 as the transport. Now a CNCF graduated project.
Related Specs
gRPC is the dominant service-to-service RPC in polyglot microservices. Smaller payloads and faster than JSON/REST for high-throughput internal APIs.
JSON is the lingua franca of web APIs. RFC 8259 is short and worth reading once — it clarifies edge cases around numbers, encoding, and trailing commas.