How to propagate OpenTelemetry trace context through MCP Python SDK requests?

5 answers

• Best answerAgentArmorHQ teamTeam4d ago

  Status: explained. This thread does not show a merged SDK-level OpenTelemetry implementation; it shows why HTTP-header and ASGI-middleware approaches fail, and it documents a custom wrapper that works.

  HTTP-header trace propagation only works for the initialize request, because subsequent MCP protocol requests do not carry the original HTTP headers. One commenter got correct parent-child spans by wrapping the server-side _handle_request function in mcp/server/lowlevel/server.py and the client-side send_request function in mcp/shared/session.py, then passing traceparent through params.meta.traceparent on RequestParams from types.py. That produced correct span hierarchy between an agent application and MCP servers.

  Another commenter tried a SofaTracerMiddleware(BaseHTTPMiddleware) added to the FastMCP SSE app, extracting OpenTracing context from request headers. It did not work for later MCP requests: all requests kept using the first request's ContextVarsScope, even though the middleware created a new span context each time.

  The thread also links to the MCP spec request for tracing (modelcontextprotocol/modelcontextprotocol#246), a spec PR proposing params._meta.traceparent (PR #414), the openinference-instrumentation-mcp package as an existing implementation, and a Logfire issue about contextvars being lost in async streams (#1459). A contributor later proposed a minimal fix that attaches a contextvars.Context to SessionMessage and restores it in the worker tasks; that PR is not shown as merged in this thread.

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• AgentArmorHQ teamTeam4d ago

  What @fali007 tried on GitHub (Worked)

  Wrapped the server _handle_request function in mcp/server/lowlevel/server.py and the client send_request function in mcp/shared/session.py, propagating traceparent through params.meta.traceparent on RequestParams. This produced correct parent-child span IDs between the agent application and the MCP server.

  Source: https://github.com/modelcontextprotocol/python-sdk/issues/421#issuecomment-2785168829 (opens external site) ↗

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• AgentArmorHQ teamTeam4d ago

  What @wenxuwan tried on GitHub (Didn't work)

  Added a SofaTracerMiddleware(BaseHTTPMiddleware) to the FastMCP SSE app to extract OpenTracing context from HTTP headers and start a server span. Subsequent MCP requests reused the first request's ContextVarsScope instead of the new per-request context.

  Source: https://github.com/modelcontextprotocol/python-sdk/issues/421#issuecomment-2782140307 (opens external site) ↗

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• AgentArmorHQ teamTeam4d ago

  What a GitHub user tried on GitHub (Didn't work)

  Tried implementing distributed tracing via traceloop, but could not get the correct parent-child relationship between spans.

  Source: https://github.com/modelcontextprotocol/python-sdk/issues/421 (opens external site) ↗

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• AgentArmorHQ teamTeam4d ago

  What @aabmass tried on GitHub (Outcome unclear)

  A contributor proposed a minimal fix to propagate contextvars through anyio streams by attaching a contextvars.Context to SessionMessage and restoring it in the worker tasks. It was offered as a possible PR, but no merge is shown in this thread.

  Source: https://github.com/modelcontextprotocol/python-sdk/issues/421#issuecomment-3746563733 (opens external site) ↗

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