fix(mcp): support MCP SDK v2 handler signature and removed request_ctx by ericapisani · Pull Request #6583 · getsentry/sentry-python · GitHub

MCP SDK v2 changed handler signatures from (name, arguments) to
(ctx, params) and removed the request_ctx ContextVar. Add version
detection to patch the correct entry-points (Server.init and
add_request_handler for v2, decorator methods for v1), extract
request context from the ServerRequestContext argument directly,
and update tests to work with both SDK versions.

Migration notes for MCP SDK v2 can be found here:

What this PR does not do:

address all breaking changes outlined in the migration guide. This is meant to fix the test failures on ci: 🤖 Update test matrix with new releases (06/15) #6567 while still being comprehensive enough to make sense for the next developer who continues the migration.

This was tested on the branch in #6567 to confirm it doesn't introduce regressions while addressing the v2 breaking change.

Fixes PY-2532
Fixes #6574

MCP SDK v2 changed handler signatures from (name, arguments) to (ctx, params) and removed the request_ctx ContextVar. Add version detection to patch the correct entry-points (Server.__init__ and add_request_handler for v2, decorator methods for v1), extract request context from the ServerRequestContext argument directly, and update tests to work with both SDK versions. Migration notes for MCP SDK v2 can be found here: - https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0a1 - https://github.com/modelcontextprotocol/python-sdk/blob/main/docs/migration.md Fixes PY-2532 Fixes #6574

PY-2532

Codecov Results 📊

✅ 90992 passed | ⏭️ 6121 skipped | Total: 97113 | Pass Rate: 93.7% | Execution Time: 326m 5s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +96
Passed Tests	📈 +12
Failed Tests	—
Skipped Tests	📈 +84

All tests are passing successfully.

❌ Patch coverage is 54.24%. Project has 2467 uncovered lines.
❌ Project coverage is 89.6%. Comparing base (base) to head (head).

Files with missing lines (1)

File	Patch %	Lines
sentry_sdk/integrations/mcp.py	54.24%	⚠️ 54 Missing and 16 partials

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    89.79%    89.60%    -0.19%
==========================================
  Files          192       192         —
  Lines        23652     23732       +80
  Branches      8154      8194       +40
==========================================
+ Hits         21238     21265       +27
- Misses        2414      2467       +53
- Partials      1344      1357       +13

Generated by Codecov Action

handler_name unbound in _extract_handler_data_from_args for tool/prompt types

In sentry_sdk/integrations/mcp.py, _extract_handler_data_from_args for handler_type == 'tool' or 'prompt' assigns handler_name only inside if original_args: / elif original_kwargs.get('name'):. If both conditions are false, handler_name is never set; the prompt branch crashes immediately at arguments = {"name": handler_name, ...} with UnboundLocalError, and the tool branch crashes at the return statement.

Evidence

_extract_handler_data_from_args lines 416–420 and 427–431 conditionally assign handler_name for 'tool' and 'prompt' but provide no else / default assignment.
For 'prompt', the unguarded arguments = {"name": handler_name, ...} at line 440 is reached before the return, crashing before instrumentation runs.
The 'resource' branch (line 443) shows the correct pattern with handler_name = "unknown" as a default.
No existing tests exercise the empty-args, empty-kwargs path for v1 tool/prompt handlers, so the gap is uncovered.
The function is called from _prepare_handler_data (line 480) on the v1 code path with whatever original_args the MCP SDK provided, so any caller that passes no positional name arg will trigger this.

Identified by Warden find-bugs

This test is relying on private implementation details, making it brittle to internal changes such as renaming _wrap_v2_handler or __sentry_mcp_wrapped__.

I'd say we can just remove the test to be honest. If we want to keep it let's ensure we don't double wrap by checking behavior observable by the user. For example, ensuring that we don't emit the same span twice (I assume that's what happens when you double wrap).

…ods rather than invoking the wrap handler method directly

Bug: The handler_name variable is not initialized in _extract_handler_data_from_args for "tool" and "prompt" types if arguments are missing, leading to an UnboundLocalError.
Severity: LOW

Suggested Fix

Initialize handler_name to a default value, such as "unknown", at the beginning of the logic for both the "tool" and "prompt" handler types. This mirrors the existing safe-handling pattern used for the "resource" type.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: sentry_sdk/integrations/mcp.py#L403-L407

Potential issue: In the `_extract_handler_data_from_args` function, when the
`handler_type` is either "tool" or "prompt", the `handler_name` variable is only
assigned a value if `original_args` is provided or if `original_kwargs` contains a
"name" key. If neither of these conditions is met, the variable is never initialized.
This will cause an `UnboundLocalError` when the code later attempts to use
`handler_name` to construct the `arguments` dictionary. This scenario can occur if a
developer invokes a v1 handler directly without passing the expected arguments,
bypassing the standard MCP SDK dispatcher.

Cursor Bugbot has reviewed your changes and found 1 potential issue.

❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.

Reviewed by Cursor Bugbot for commit 787e77a. Configure here.

v1 SSE test wrong assertion

Medium Severity

test_sse_transport_detection is skipped on MCP v2 and only runs on v1, but it asserts result["result"]["structuredContent"], which is a v2 JSON-RPC shape. The v1 handler returns a plain dict and the json_rpc_sse fixture waits for a result with content, so this assertion fails on v1 runs.

Reviewed by Cursor Bugbot for commit 787e77a. Configure here.

getsentry#6583) MCP SDK v2 changed handler signatures from (name, arguments) to (ctx, params) and removed the request_ctx ContextVar. Add version detection to patch the correct entry-points (Server.__init__ and add_request_handler for v2, decorator methods for v1), extract request context from the ServerRequestContext argument directly, and update tests to work with both SDK versions. Migration notes for MCP SDK v2 can be found here: - https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.0.0a1 - https://github.com/modelcontextprotocol/python-sdk/blob/main/docs/migration.md What this PR does not do: - address all breaking changes outlined in the migration guide. This is meant to fix the test failures on getsentry#6567 while still being comprehensive enough to make sense for the next developer who continues the migration. This was tested on the branch in getsentry#6567 to confirm it doesn't introduce regressions while addressing the v2 breaking change. Fixes PY-2532 Fixes getsentry#6574

ericapisani marked this pull request as ready for review June 16, 2026 14:41

ericapisani requested a review from a team as a code owner June 16, 2026 14:41

cursor Bot reviewed Jun 16, 2026

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Comment thread sentry_sdk/integrations/mcp.py

Comment thread sentry_sdk/integrations/mcp.py Outdated

fix logic issue

5b28fb5

sentry Bot reviewed Jun 16, 2026

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Comment thread sentry_sdk/integrations/mcp.py

sentry-warden Bot reviewed Jun 16, 2026

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Comment thread tests/integrations/mcp/test_mcp.py

remove tests that were directly exercising the handler method

eb09e69

alexander-alderman-webb reviewed Jun 17, 2026

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alexander-alderman-webb approved these changes Jun 17, 2026

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Comment thread tests/integrations/mcp/test_mcp.py

Rework the idempotency test to test the functionality via public meth…

6247168

…ods rather than invoking the wrap handler method directly

sentry Bot reviewed Jun 17, 2026

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ericapisani mentioned this pull request Jun 17, 2026

Propagate context variables in the SSE transport within the MCP integration #6593

Open

Merge branch 'master' into py-2532-handle-removal-of-request_ctx

787e77a

cursor Bot reviewed Jun 17, 2026

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ericapisani merged commit 89b3ebb into master Jun 17, 2026
144 checks passed

ericapisani deleted the py-2532-handle-removal-of-request_ctx branch June 17, 2026 14:34

sentry-release-bot Bot mentioned this pull request Jun 30, 2026

publish: getsentry/sentry-python@2.64.0 getsentry/publish#8744

Closed

6 tasks

tejas7777 mentioned this pull request Jul 7, 2026

sentry_sdk.init() slowed by module-level package_version("mcp") scanning all installed distributions (2.64.0) #6769

Open

mangodxd mentioned this pull request Jul 23, 2026

perf: Avoid scanning installed packages when MCP SDK is not installed #6865

Merged

+              def test_wrap_v2_handler_is_idempotent():
+                  """_wrap_v2_handler must not double-wrap a handler registered through more
+                  than one path (e.g. MCPServer building a Server, then re-registration)."""
+                  import sentry_sdk.integrations.mcp as mcp_module
+                  async def handler(ctx, params):
+                      return None
+                  wrapped = mcp_module._wrap_v2_handler("tool", handler)
+                  assert wrapped is not handler
+                  assert getattr(wrapped, "__sentry_mcp_wrapped__", False) is True
+                  rewrapped = mcp_module._wrap_v2_handler("tool", wrapped)
+                  assert rewrapped is wrapped

                   original_args: "tuple[Any, ...]",
                   original_kwargs: "Optional[dict[str, Any]]" = None,
-              ) -> "tuple[str, dict[str, Any], str, str, str, Optional[str]]":
+              ) -> "tuple[str, dict[str, Any]]":
                   """
-                  Prepare common handler data for both async and sync wrappers.
+                  Extract handler name and arguments from v1 positional args.

fix(mcp): support MCP SDK v2 handler signature and removed request_ctx by ericapisani · Pull Request #6583 · getsentry/sentry-python · GitHub

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fix(mcp): support MCP SDK v2 handler signature and removed request_ctx - #6583

fix(mcp): support MCP SDK v2 handler signature and removed request_ctx#6583
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+                      @server.call_tool()
+                      async def test_tool(tool_name, arguments):
+                          return {"result": "success"}

fix(mcp): support MCP SDK v2 handler signature and removed request_ctx by ericapisani · Pull Request #6583 · getsentry/sentry-python · GitHub

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fix(mcp): support MCP SDK v2 handler signature and removed request_ctx - #6583

fix(mcp): support MCP SDK v2 handler signature and removed request_ctx#6583ericapisani merged 5 commits intomastergetsentry/sentry-python:masterfrom py-2532-handle-removal-of-request_ctxgetsentry/sentry-python:py-2532-handle-removal-of-request_ctxCopy head branch name to clipboard

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v1 SSE test wrong assertion

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fix(mcp): support MCP SDK v2 handler signature and removed request_ctx#6583
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