Topic 5: Observability

Tracing a question end to end

A trace is the story of one request across every process it touches, made of spans: timed operations with a name, attributes, and a parent. The trace id is shared by every span in the story; each span's parent id says what called it. OpenTelemetry (OTel) is the open standard for producing them, and the W3C traceparent header (or field) is how a trace id crosses a process boundary.

The MCP Python SDK is already instrumented. Every inbound message becomes a SERVER span such as tools/call search_notes, every outbound request a CLIENT span such as MCP send tools/call search_notes, and the client puts traceparent into the request's _meta so the server span joins the client's trace. The 2026-07-28 specification documents those _meta keys (traceparent, tracestate, baggage) from SEP-414. All of it is a no-op until you install the OTel SDK and an exporter, which is what the setup step did.

The example traces one host question through the server into a downstream HTTP API. Everything runs in one process so that one in-memory exporter sees all spans; in production each process exports to the same collector and the trace ids join them.