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MCP Tools assigns external tool servers to the agent. When configured, the agent can call these tools during a conversation to fetch data, take actions, or interact with external systems.

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Selecting MCP servers

Choose from the list of servers registered in Settings → MCP Servers. You can assign multiple servers to a single agent. Each selected server exposes its full set of tools to the agent at runtime.
Adding MCP servers automatically switches the evaluation strategy to react. This is required — react is the strategy that enables the tool-use loop where the agent reasons, calls tools, observes results, and repeats. You can override this in Dev Mode.

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How tool use works at runtime

When the agent receives a message:
  1. The Runtime fetches tool schemas from all assigned MCP servers
  2. These schemas (tool names, descriptions, input parameters) are injected into the LLM prompt
  3. If the LLM decides to call a tool, the Runtime executes it and returns the result
  4. The LLM incorporates the result and continues reasoning
  5. This loop repeats until the agent has enough information to respond

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Writing good tool descriptions

The agent decides which tool to call and when based on tool names and descriptions. If a tool description is vague, the agent may misuse it or ignore it entirely. Good tool description: “Retrieves a customer’s order history. Input: customer_id (string). Returns: list of orders with status, date, and amount.” Bad tool description: “Gets orders.” Tool descriptions are set in the MCP server itself, not in Studio.

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Next steps

Agent-to-Agent

Delegate tasks to other agents instead of tools.

Dev Mode

Override the evaluation strategy or customize how tools are presented in the prompt.