feat(develop): Add distributed tracing for MCP #15752
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betegon
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Looks good!
btw we don't support mcp clients, is something we're considering now?
| ## Distributed Tracing | ||
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| Traces should be continued when a client makes a tool call request to an MCP server and both the client and server are instrumented. To do so, we inject both the trace parent (sentry-trace) and baggage into the `_meta` field of the request, and pick these up on the server. The tracing metadata attached in the `_meta` field is the same as the metadata contained in HTTP headers in HTTP-based trace continuation. | ||
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| The SDK must respect any existing metadata in `_meta`. If previously empty, the `_meta` field must have the form | ||
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| ```json | ||
| "_meta": { | ||
| "sentry-trace": "...", | ||
| "baggage": "...", | ||
| } | ||
| ``` | ||
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| where "sentry-trace" is analogous to the [`sentry-trace` HTTP header](/sdk/telemetry/traces/#header-sentry-trace) and "baggage" is analogous to [`baggage` HTTP header](/sdk/telemetry/traces/dynamic-sampling-context/#baggage-header). |
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Maybe we can already think about how we can support mixed OTLP/Sentry instrumentation here. As in, can we rely on the traceparent header instead of our sentry-tace header?
Also, which options should define if we perform propagation? tracePropagationTargets or something new?
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good call, I don't see any reason we shouldn't use traceparent instead of sentry-trace for MCP.
I should also spec out what happens over Streamable HTTP. Both headers and MCP _meta can be used to propagate tracing metadata in that case, but headers have the limitation that in Streamable HTTP there's one connection for multiple tool calls.
In terms of options, we could have tracePropagationTargets for tool names instead of URLs. See the params.name field in tools/call requests:
https://modelcontextprotocol.io/specification/2025-06-18/server/tools#calling-tools
But tracePropagationTargets should probably still apply when the MCP is mounted on HTTP.
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Add specification for trace propagation over the MCP protocol.
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