Every AI agent integration starts the same way: someone wires a chatbot to a REST API and calls it a day. It works, right up until the agent needs to chain three operations together and the API's assumptions about a human clicking buttons in order start to show.
MCP (Model Context Protocol) flips that. Instead of retrofitting REST for agents, you expose the same domain operations as typed, discoverable tools — the agent doesn't scrape a Swagger doc and guess, it gets a tool with a name, a schema, and a description built for reasoning.
The part nobody warns you about: keeping REST and MCP in sync. My rule is protocol isomorphism — one operation definition, two adapters. Define the operation once (HTTP method + path, MCP tool name + schema), and both a React frontend and a reasoning agent call the exact same business logic. Zero duplication, zero drift.