How to set / get `client_id`?

[samirbajaj]

I'd like to be able to retrieve the client_id from inside a tool call on an MCP server. However, it is always None. What do I need to set in the MCP client in order to be able to retrieve it on the server?

The client code is basically taken from the documentation:

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

server_params = StdioServerParameters(
    command="python",  # Executable
    args=["example_server.py"],  # Optional command line arguments
    env=None,  # Optional environment variables
)


async def run():
    async with stdio_client(server_params) as (read, write):
        async with ClientSession(
            read, write
        ) as session:
            # Initialize the connection
            await session.initialize()

            # Call a tool
            result = await session.call_tool("my_tool")

The tool function is as follows:

mcp = FastMCP("docint")

@mcp.tool()
async def my_tool(ctx: Context) -> Optional[str]:
    """
    Extracts client ID and request ID from the context.

    Returns:
        client ID and request ID from the context.
    """
    return f"{ctx.client_id} {ctx.request_id}" # <----- THIS

This prints None 2 (client_id as None).

What am I missing?

Thank you.

[JorgeRuizITCL]

I have the exact same question, but i think that this is a WIP feature that will be implemented based on this draft.

[samirbajaj]

Can one of the contributors or maintainers confirm if this is supposed to work, please?

Or is it broken / WIP as the above comment suggests?

Thank you.