API Architectural Styles

An API architectural style is the set of conventions an API follows for how clients express intent, how servers expose capability, how failures are reported, how contracts evolve, and how traffic behaves under load. REST, GraphQL, gRPC, WebSocket, Server-Sent Events, webhooks, SOAP, and message-driven APIs each fit a different communication problem.

A public product API needs predictable HTTP behavior, caching, documentation, and broad client support. A mobile screen may need one round trip across many backend systems. A model-serving path may need strict schemas, deadlines, and streaming tokens. A payment provider needs to notify another server after a charge settles. Those are different API problems and no single style is the right answer for all of them.

Good API architecture starts with the interaction pattern, then chooses the style that fits it.