LLM Tool Use in MCP Servers

You've built an MCP server containing a tool for converting currencies using up-to-date exchange rates. Integrating it with an LLM will give it the ability to accurately answer questions about currencies and exchange rates—something it can't do by default.

The bulk of the code is provided for you here, as the main focus should be on understanding the workflow rather than syntax.

This exercise is part of the course

Introduction to Model Context Protocol (MCP)

View Course

Exercise instructions

Send the user query (user_query) and formatted list of tools (anthropic_tools) to Claude.
Call the MCP tool chosen by the LLM, using the name and arguments extracted from the tool use block.
Send the result (result) back to Claude for the final response.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client

async def call_anthropic_llm(user_query: str):
    """Call Claude with MCP tools."""
    
    print(f"\nUser: {user_query}\n")

    mcp_tools = await get_tools_from_mcp()
    
    anthropic_tools = []
    for tool in mcp_tools:
        anthropic_tool = {
            "name": tool.name,
            "description": tool.description or "",
            "input_schema": tool.inputSchema,
        }
        anthropic_tools.append(anthropic_tool)
    
    # Send the user query and formatted tools to the LLM
    client = AsyncAnthropic(api_key="")

    response = await client.messages.create(
        model="claude-sonnet-4-6",
        max_tokens=1024,
        messages=____,
        tools=____,
    )

    if response.stop_reason == "tool_use":
        tool_use = next(block for block in response.content if block.type == "tool_use")
        name = tool_use.name
        args = tool_use.input

        print(f"Model decided to call: {name}")
        print(f"Arguments: {args}\n")

        # Call the MCP tool
        result = await call_mcp_tool(____, ____)

        # Send the result back to Claude for the final response
        followup = await client.messages.create(
            model="claude-sonnet-4-6",
            max_tokens=1024,
            messages=[
                {"role": "user", "content": user_query},
                {"role": "assistant", "content": response.content},
                {
                    "role": "user",
                    "content": [
                        {
                            "type": "tool_result",
                            "tool_use_id": tool_use.id,
                            "content": ____,
                        }
                    ],
                },
            ],
            tools=anthropic_tools,
        )

        final_text = next((block.text for block in followup.content if block.type == "text"), None)
        if final_text:
            print(f"\nAssistant: {final_text}")
            return str(final_text)
        else:
            print("No follow-up message from model.")

    else:
        text = next((block.text for block in response.content if block.type == "text"), "")
        print(f"\nAssistant: {text}")
        return str(text)


if __name__ == "__main__":
    asyncio.run(call_anthropic_llm("How much is 250 US dollars in euros?"))

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