Definition
An MCP host is the AI application that coordinates users, models, policy, and connections to one or more MCP servers. It creates a separate MCP client for each server connection, decides which exposed capabilities enter the application, and mediates how model requests become protocol actions.
Examples of hosts include AI desktop applications, coding environments, and agent runtimes. The host owns application-level concerns that no individual server can see: user identity, consent, conversation state, model selection, capability routing, data boundaries, and the combined risk of several servers operating in one session.
The host is the policy choke point
Servers can describe security schemes and validate requests, but the host decides whether a tool should be shown to this model and user, whether a resource may enter context, and whether an action requires confirmation. A weak host can turn individually narrow servers into broad combined authority.
Distinguish it from nearby terms
The host is the user-facing AI application. An MCP client is the per-server protocol component it maintains. An MCP server exposes tools, resources, or prompts. The model may select among surfaced capabilities, but it is not normally the host or protocol client.
Check your understanding
Two servers are safe in isolation: one reads customer records and one sends email. Together they can disclose private data. Which component can see and control that composition? The host. Its policy must evaluate cross-server data flow, not only each call separately.