What is an API Endpoint?

An endpoint is the concrete, addressable unit of an API's surface — `GET /users/123` and `POST /users` are two different endpoints, even on the same resource, because they do different things and typically accept and return different payloads. A full API is really a collection of these individually documented endpoints, each with its own required parameters, authentication needs, and response shape. Good endpoint design keeps each one focused on a single, predictable responsibility rather than an overloaded operation that behaves differently depending on hidden flags — this predictability is what lets client code, documentation, and automated tooling reason about the API without surprises. Endpoints are also the natural unit for rate limiting, permission scoping, and monitoring, since usage patterns and failure modes often differ sharply between, say, a read endpoint and a write endpoint. For an AI agent calling out to external tools, each callable capability maps to one or more specific endpoints — the agent's tool definition is essentially a structured description of which endpoint to hit and with what parameters, translated from the user's natural-language intent.