How to add per-request trace_id (UUID) to all logs in FastMCP?

[berkaytor]

Enhancement Description

I'm working on a project that uses FastMCP, and I'd like to generate a unique trace_id (UUID) for every incoming request and ensure that it's included in all log messages during that request's lifecycle.

I’m currently starting the server like this:

from fastmcp import FastMCP

mcp = FastMCP(name="MyServer")
mcp.run(
    transport="sse",
    uvicorn_config={"access_log": False}
)

What I’m trying to do:

• Generate a UUID per incoming request (HTTP or SSE).

• Propagate it across the entire request lifecycle, including exception handlers.

• Print it in every log entry, so I can trace logs for a single request easily.

• Ideally, inject this into existing loggers via a logging filter or similar.

My questions:

• Is there a recommended way to attach a middleware to FastMCP apps created via mcp.run() or mcp.sse_app()?

• Can I retrieve the underlying FastAPI/Starlette app from FastMCP and add custom middleware (e.g., to set a ContextVar)?

• Would it be reasonable to inject a trace_id using contextvars and a logging.Filter to modify log records?

• Is there any existing support in FastMCP for per-request logging context?

If others have done something similar, I’d love to see an example!

Thanks in advance

Use Case

No response

Proposed Implementation

[ifoukarakis]

Adding a unique ID is possible using a middleware such as asgi-correlation-id. However the logic differs on Streamable HTTP and SSE, as the underlying transport is different. For example, in SSE the connection from the server to the client is a long one. Thus all responses from the server will share the same correlation id. It will also be different than the request ID in the POST to /messages.

If there's a need to have a correlation ID that links request and response, then I think it requires a new solution. Perhaps something can be done by combining #599 with the solution of #596.