REST is human-readable and universally supported. gRPC offers binary encoding, strongly typed contracts, bidirectional streaming, and generated clients — making it superior for internal high-throughput service communication.
Human-readable JSON — easy to debug with curl and browser dev tools
Universal client support — any language, any HTTP client
Cacheable with HTTP semantics (GET, ETags, Cache-Control)
Easier to expose as a public API — developers understand it
No code generation required
Protocol Buffers: binary encoding is 3-10x smaller and faster to encode/decode than JSON
Strongly typed contracts: .proto files are the source of truth, generated client/server code
Bidirectional streaming: server streaming, client streaming, and full-duplex streams
Deadlines propagated across calls automatically via context
Built-in load balancing, health checking, and flow control