feat: add OpenTelemetry tracing for client and server requests #2025
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Add opentelemetry-api as a dependency and instrument BaseSession.send_request() with a CLIENT span per outgoing request. This establishes the tracing foundation for the SDK. Each request gets a span with the MCP method name and, where applicable, the target name (tool name, prompt name, resource URI). Spans record OK/ERROR status and error type attributes. Excluded methods (e.g. notifications/message) are skipped.
Kludex
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Feb 10, 2026
tests/shared/test_tracing.py
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| # pyright: reportMissingImports=false, reportUnknownVariableType=false | ||
| # pyright: reportUnknownMemberType=false, reportUnknownParameterType=false | ||
| # pyright: reportUnknownArgumentType=false | ||
| # opentelemetry-sdk does not ship type stubs, so we suppress unknown-type errors. |
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It seems it does. I can see the py.typed.
Kludex
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Feb 10, 2026
src/mcp/shared/session.py
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| # Store the callback for this request | ||
| self._progress_callbacks[request_id] = progress_callback | ||
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| method = request_data.get("method", "") |
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Is there a case that we don't have a method?
Kludex
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Feb 10, 2026
src/mcp/shared/tracing.py
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| def _build_span_name(method: str, target: str | None) -> str: | ||
| """Build a span name like 'tools/call my_tool' or just 'ping'.""" | ||
| if target: | ||
| return f"{method} {target}" | ||
| return method |
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No need for this utility.
Kludex
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Feb 10, 2026
tests/shared/test_tracing.py
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| async with create_client_server_memory_streams() as (client_streams, server_streams): | ||
| client_read, client_write = client_streams | ||
| server_read, server_write = server_streams |
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Is it possible to use mcp.client.Client instead?
Kludex
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Feb 10, 2026
tests/shared/test_tracing.py
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| @pytest.mark.parametrize( | ||
| ("method", "target", "expected"), | ||
| [ | ||
| ("tools/call", "my_tool", "tools/call my_tool"), | ||
| ("ping", None, "ping"), | ||
| ], | ||
| ) | ||
| def test_build_span_name(method: str, target: str | None, expected: str) -> None: | ||
| assert _build_span_name(method, target) == expected |
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We shouldn't test private functions! Please document that in the CLAUDE.md.
Kludex
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Feb 10, 2026
tests/shared/test_tracing.py
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| @pytest.mark.parametrize( | ||
| ("method", "params", "expected"), | ||
| [ | ||
| ("tools/call", {"name": "my_tool"}, "my_tool"), | ||
| ("prompts/get", {"name": "my_prompt"}, "my_prompt"), | ||
| ("resources/read", {"uri": "file:///a.txt"}, "file:///a.txt"), | ||
| ("ping", None, None), | ||
| ("tools/call", {}, None), | ||
| ("tools/call", {"name": 123}, None), | ||
| ], | ||
| ) | ||
| def test_extract_target(method: str, params: dict[str, Any] | None, expected: str | None) -> None: | ||
| assert _extract_target(method, params) == expected |
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We shouldn't test private functions! Please document that in the CLAUDE.md.
- Remove pyright suppressions (opentelemetry-sdk ships py.typed)
- Use `request_data["method"]` instead of `.get("method", "")`
- Inline `_build_span_name` into `start_client_span`
- Remove unit tests for private functions, test through E2E instead
- Rewrite error test to use `Client` (timeout-based)
- Add "do not test private functions" rule to CLAUDE.md
Kludex
commented
Feb 10, 2026
src/mcp/shared/session.py
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| # Store the callback for this request | ||
| self._progress_callbacks[request_id] = progress_callback | ||
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| method: str = request_data["method"] |
Code reviewNo issues found. Checked for bugs and CLAUDE.md compliance. |
Instrument the server side of MCP request handling with OpenTelemetry SERVER spans. The span starts after request validation in _receive_loop and ends when RequestResponder.respond() or cancel() is called, covering the full server-side request lifecycle.
Kludex
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Kludex
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Feb 10, 2026
src/mcp/shared/session.py
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| server_span = start_server_span( | ||
| request_data.get("method", ""), | ||
| request_data.get("params"), | ||
| ) |
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Single line please. Is the method not always available in request_data?
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Summary
opentelemetry-apias a runtime dependency andopentelemetry-sdkas a dev dependencysrc/mcp/shared/tracing.pywith a module-level tracer, attribute constants, and helpers for span naming (including target extraction fortools/call,prompts/get,resources/read)BaseSession.send_request()with a singleCLIENTspan per outgoing request — records method name, target, OK/ERROR status, and error typenotifications/message) produce no spanThis is the minimal foundation for OpenTelemetry support. No context propagation, metrics, or server-side spans yet — just one client-side span per request to establish the pattern.
Test plan
_extract_target()and_build_span_name()helpers (parametrized)send_ping()tools/callrequestserror.typeattribute on JSON-RPC error responseruff format+ruff checkpasspyrightstrict passes (0 errors)