The MCP Protocol

You wrote a connector to your data warehouse for your internal agent. The support team wants one for their own assistant, which doesn't use the same SDK. The team's code editor wants one too, with its own convention for declaring tools. Three integrations, three schema formats, three error policies, and a single piece of business logic — duplicated three times, then out of sync as soon as the order schema changes for the first time.

The Model Context Protocol addresses exactly this problem and no other. It is a transport and discovery protocol: it defines how a program announces the tools, data, and prompt templates it exposes, how a host discovers them at runtime, and in what format the results come back. It doesn't make your agent smarter, it doesn't decide permissions, and it doesn't replace the quality of descriptions covered in the previous lesson. What it provides is more modest and more useful: you write the connector once, and any compatible host can plug into it.

The Vocabulary

Three roles, not to be confused.

The host is the application the user interacts with: a code editor, a chat client, your own agent. It talks to the model and decides what to allow.