What is MCP (Model Context Protocol)?

MCP (Model Context Protocol), explained#

Before MCP, every AI assistant needed its own plugin format. A company that wanted its data in three assistants built three integrations, each with its own authentication and its own idea of what a function call looks like. MCP replaces that with one protocol: build a server once and any compliant client can use it.

Anthropic introduced MCP as an open standard in November 2024. The specification is versioned by date; the current revision at the time of writing is 2025-11-25. It borrows its shape from the Language Server Protocol, which did the same job for code editors and programming languages.

There are three roles. The host is the AI application a person uses, such as Claude Desktop, ChatGPT, Cursor or a custom agent. Inside the host, an MCP client holds one connection to one MCP server. The server is the program that exposes capabilities. Messages are JSON-RPC 2.0 requests, responses and notifications, and the two sides negotiate which features each supports when they connect.

A server can offer three kinds of thing. Tools are functions the model may call, like create_issue. Resources are read-only context identified by a URI, like a file or a record. Prompts are reusable message templates a person picks, often shown as slash commands. Clients can in turn offer servers sampling (asking the host's model to generate text), roots (filesystem boundaries) and elicitation (asking the user a question).

MCP defines two standard transports. stdio runs the server as a local subprocess and passes messages over standard input and output. Streamable HTTP puts the server behind one HTTPS endpoint, which is what makes a remote MCP server possible. For HTTP servers, the specification's authorization section builds on OAuth 2.1.

For example, a founder connects Claude to their project tracker's MCP server. They ask, "What is overdue this week?" Claude lists the server's tools, calls the one that searches work with a due-date filter, reads the JSON result and answers in a sentence, without the founder opening the tracker.