What is an MCP Host?

The host is the outermost layer in MCP's three-part architecture (host, client, server). It's responsible for things the protocol itself doesn't specify: which servers to connect to, how to present tool results to the user, how to merge multiple servers' capabilities into one coherent experience, and how to enforce its own security policy on top of whatever a server requests. A single host commonly manages several client instances at once, each maintaining a separate connection to a different server. Because the host owns the user-facing surface, it's also where consent and trust decisions live — deciding whether to surface a tool call for approval, whether to auto-run certain low-risk actions, and how to display resources or prompts a server exposes. This keeps the servers themselves simple and stateless with respect to UI concerns; they describe capabilities, and the host decides how those capabilities reach the user. Examples of hosts include desktop AI assistants, code editors with AI integration, and custom agent runtimes — anything that both talks to a model and manages MCP client connections on the model's behalf.