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Model Context Protocol (MCP) is how you add external tool servers to the agent. Fleet Prime Agent treats every registered MCP tool as a normal AgentTool — the model can call it, the runtime renders it as a card, and you don’t need any custom glue on the agent side.

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Register a server

MCP servers are exposed through the extension runtime (packages/coding-agent/src/core/extensions/). Register an MCP-capable extension the same way you register any other extension:
Or add it to your project or personal extension config so it loads every time. See Extensions for the config paths.

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How it looks to the model

Once registered, the MCP server’s tools appear in the model’s tool list. Each tool implements the standard AgentTool interface (execute, prepareArguments) so the model treats it identically to a built-in tool. Tool cards render the same way as tool cards for shell or IPython.

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Capability gating

If an MCP extension affects daemon behavior (not just adds tools), it must sit behind a negotiated capability gate. The daemon protocol won’t send new commands to clients that didn’t advertise the capability, so mixed old-client / new-daemon setups keep working. See Daemon protocol.
Last modified on August 17, 2026