REST APIs gave humans (and the code they wrote) a standardized way to access software over the network. MCP is trying to do the same thing for agents. That simple framing clears up a lot of confusion. For nearly 20 years we built systems assuming the caller was a human developer writing code against APIs. Now the caller is increasingly an LLM-driven agent. MCP changes the interface layer accordingly. The REST Era: APIs Designed for Humans With REST + OpenAPI, the typical flow looked like this: Human Developer ↓ SDK / HTTP Client ↓ REST API ↓ Service Enter fullscreen mode Exit fullscreen mode A human would read the docs, inspect the OpenAPI spec, figure out auth, pick the right endpoints, map parameters, handle retries and errors, and manually compose workflows. OpenAPI became the universal machine-readable description of the API. It captured endpoints, request/response schemas, authentication, parameters, types, and examples.…