APIs

Six lessons covering how APIs work — the interfaces between every service, client, and system.

REST (resources, HTTP verbs, statelessness, and status codes), GraphQL (schemas, queries, resolvers, and the N+1 problem), gRPC (Protocol Buffers, HTTP/2, and streaming patterns), WebSockets (persistent connections, the upgrade handshake, and real-time data), API authentication (API keys, OAuth 2.0, JWT, and session-based auth), and rate limiting (token bucket, sliding window, and distributed enforcement).

Every networked application communicates through APIs. Understanding how they work — which protocol to choose, how to authenticate, how to handle failure — is the difference between systems that compose cleanly and systems that break under load. The glossary defines every term. The FAQ answers common questions.