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feat(mcp): tag server spans with client info - #21189
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Runtime compatibility remains unverified because the MCP SDK is not installed. The completed static review found no reportable defect in the client-info lookup or tag emission.
🤖 Bits Code Review · Commit ad335eb
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…nt info Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Would be nice to have an example trace to show this working E2E, but otherwise LGTM!
…ity spans Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
## Description Adds support for `mcp` 2.x. mcp 2.0 removed `mcp.shared.session` (`BaseSession`, `RequestResponder`), so `patch()` hit an `ImportError` and silently skipped instrumentation. mcp 2.x is also the only Python SDK that speaks the stateless 2026-07-28 protocol (no `initialize` handshake, no `Mcp-Session-Id`). - Server: a Datadog middleware is added to `Server.middleware` when a `ServerRunner` is built. Every transport and protocol version builds one per connection and runs each inbound message through the middleware, so servers constructed before `patch()` are traced too. It produces the same spans, tags, distributed tracing and intent capture as the 1.x `RequestResponder` patches, for both handshake and stateless clients. Client info comes from the session's `client_params`, which mcp 2.x fills from either the handshake or the request envelope. Reserved `io.modelcontextprotocol/*` `_meta` keys are left out of the recorded input. - Client: existing `ClientSession` wrappers handle snake_case fields (`is_error`, `server_info`), `ClientSession.adopt()` (used by every stateless negotiation path) tags the session with server info so stateless clients still get `mcp_server_name`, and trace context is injected into mcp 2.x request models. - Shared server tagging between 1.x and 2.x. ## Testing New `test_mcp_v2.py` covers tool calls, tool errors and intent capture in both `legacy` (handshake) and `auto` (stateless) client modes. `Client(server)` runs the server in the client's context, which hides broken `_meta` propagation, so distributed tracing (enabled and disabled) and servers constructed before `patch()` are tested over separate memory streams. v1 test files are skipped on 2.x and vice versa. `test_mcp_patch.py` asserts the right wrapped functions per major. Suitespec adds an `mcp<2` variant so the latest 1.x stays tested while the unpinned `mcp` variant now resolves to 2.x. - [Before trace](https://app.datadoghq.com/api/v2/switch_to_user/a1ff33a1-3eb2-11f0-977a-966bfc9ad571?next=%2Fllm%2Ftraces%3Fend%3D1792785357085%26paused%3Dtrue%26query%3Dtrace_id%253A6adbbaa10000000052cb4d9cd1de767f%26start%3D1792784757040&flow=org_switch) - [After trace](https://app.datadoghq.com/api/v2/switch_to_user/a1ff33a1-3eb2-11f0-977a-966bfc9ad571?next=%2Fllm%2Ftraces%3Fend%3D1792785358714%26paused%3Dtrue%26query%3Dtrace_id%253A6adbbaa2000000009c15923d0e15c1dc%26start%3D1792784758672&flow=org_switch) ## Risks mcp 2.x marks `Server.middleware` as provisional. The middleware reads its context defensively and falls back to the plain handler, so an incompatible SDK change drops MCP server spans instead of failing requests. ## Additional Notes Stacked on #21189. Includes test requirement locks for the `mcp<2` (1.30.0) and unpinned `mcp` (2.3.0) environments, plus the regenerated integration registry. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-authored-by: max.zhang <max.zhang@datadoghq.com>
Description
Tags MCP server
initializeand tool call spans with the calling client's self-reported identity:mcp_client_name,mcp_client_title,mcp_client_version.Previously client info was only on the server
initializespan, so tool calls could only be tied to a client by joining onmcp_session_id(streamable HTTP only). The server session already stores the handshake'sclientInfo, so tool call spans now read it directly. Existingclient_name/client_versiontags are unchanged.Values are capped at 256 characters since they are client-supplied and repeated on every tool call span.
Known limitation: on mcp 1.x servers using stateless streamable HTTP (
stateless_http=True), each request gets a freshServerSessionwith no storedclient_params, and 1.x tool calls do not carryclientInfo, so those tool call spans have nomcp_client_*tags. There is no session ID to correlate them with the earlierinitialize. The 2026-07-28 protocol (mcp 2.x, follow-up PR) sendsclientInfoon every request, which closes this gap.Testing
Updated expected tags in existing LLMObs tests. Added
test_server_tool_call_tagged_with_client_info(custom client info on a tool call),test_client_info_tags_are_truncated(256-character cap) andtest_client_info_tags_empty_without_client_info(no client info, as on stateless HTTP).llmobs/mcpCI passed on mcp 1.10 and latest 1.x.Risks
None. Additive tags only.
Additional Notes
Follow-up PR adds mcp 2.x support.
🤖 Generated with Claude Code