fix(mcp): report the Python package version (#921)

Author: marandaneto

.sampo/changesets/somber-runesinger-tuonetar.md

@@ -0,0 +1,5 @@
+---
+pypi/posthog: patch
+---
+
+Report the Python package version in MCP event metadata and request headers so SDK Health can assess the installed package.

posthog/mcp/README.md

@@ -16,10 +16,10 @@ analytics = instrument(server, posthog)
 Install is just `pip install posthog`. `instrument()` needs the MCP SDK at runtime,
 but anyone wrapping a server already has it.
 
-MCP analytics events report `$lib: "posthog-python-mcp"`. Because `$lib` is a
-client-level identity, `instrument()` relabels every event sent by the client passed
-to it. Use a client dedicated to MCP analytics if the application also captures
-unrelated events.
+MCP analytics events report `$lib: "posthog-python-mcp"` and the installed `posthog` package version in `$lib_version`.
+Request headers use the same identity and package version, so SDK Health can compare MCP traffic with Python SDK releases.
+Because `$lib` is a client-level identity, `instrument()` relabels every event sent by the client passed to it.
+Use a client dedicated to MCP analytics if the application also captures unrelated events.
 
 ## Stateless / multi-pod servers
 

posthog/mcp/_lib_identity.py

@@ -3,13 +3,13 @@
 from __future__ import annotations
 
 from ..client import Client
+from ..version import VERSION
 
 from .constants import POSTHOG_MCP_LIB_NAME
-from .version import __version__
 
 
 def apply_mcp_lib_identity(client: Client) -> None:
     """Relabel every event sent by ``client`` as coming from ``posthog.mcp``."""
     set_identity = getattr(client, "_set_library_identity", None)
     if set_identity is not None:
-        set_identity(POSTHOG_MCP_LIB_NAME, __version__)
+        set_identity(POSTHOG_MCP_LIB_NAME, VERSION)

posthog/test/mcp/test_no_crash.py

@@ -11,8 +11,8 @@
 
 from posthog.client import Client
 from posthog.mcp import instrument
-from posthog.mcp.version import __version__ as MCP_VERSION
 from posthog.test.mcp._helpers import MCP_MAJOR, FakeClient
+from posthog.version import VERSION
 
 
 async def test_unsupported_server_returns_noop_handle():
@@ -75,7 +75,7 @@ def before_send(event):
     client.capture("after instrumentation")
 
     assert captured[0]["properties"]["$lib"] == "posthog-python-mcp"
-    assert captured[0]["properties"]["$lib_version"] == MCP_VERSION
+    assert captured[0]["properties"]["$lib_version"] == VERSION
 
 
 @pytest.mark.parametrize(

posthog/test/mcp/test_posthog_mcp.py

@@ -4,11 +4,11 @@
 
 from posthog.capture_mode import CaptureMode
 from posthog.mcp import PostHogMCP
-from posthog.mcp.version import __version__ as MCP_VERSION
 from posthog.test.mcp._helpers import (
     events_named as _events,
     flush_background as _flush,
 )
+from posthog.version import VERSION
 
 
 def make_client():
@@ -73,7 +73,7 @@ def before_send(event):
     assert {event["event"] for event in captured} == {"$mcp_tool_call", "$exception"}
     assert all(
         event["properties"]["$lib"] == "posthog-python-mcp"
-        and event["properties"]["$lib_version"] == MCP_VERSION
+        and event["properties"]["$lib_version"] == VERSION
         for event in captured
     )
 
@@ -86,7 +86,7 @@ def test_mcp_library_identity_reaches_capture_v0_header():
         client.capture("$mcp_custom")
 
     assert post.call_args.kwargs["headers"]["User-Agent"] == (
-        f"posthog-python-mcp/{MCP_VERSION}"
+        f"posthog-python-mcp/{VERSION}"
     )
 
 
@@ -95,10 +95,10 @@ def test_mcp_library_identity_reaches_capture_v1_header():
     with mock.patch("posthog.client._send_v1_batch") as send:
         client.capture("$mcp_custom")
 
-    assert send.call_args.kwargs["sdk_info"] == f"posthog-python-mcp/{MCP_VERSION}"
+    assert send.call_args.kwargs["sdk_info"] == f"posthog-python-mcp/{VERSION}"
     event = send.call_args.args[2][0]
     assert event["properties"]["$lib"] == "posthog-python-mcp"
-    assert event["properties"]["$lib_version"] == MCP_VERSION
+    assert event["properties"]["$lib_version"] == VERSION
 
 
 def test_mcp_library_identity_reaches_feature_flag_requests():
@@ -112,7 +112,7 @@ def test_mcp_library_identity_reaches_feature_flag_requests():
         client.evaluate_flags("user_1")
 
     assert post.call_args.kwargs["headers"]["User-Agent"] == (
-        f"posthog-python-mcp/{MCP_VERSION}"
+        f"posthog-python-mcp/{VERSION}"
     )
 
 
@@ -130,7 +130,7 @@ def test_mcp_library_identity_reaches_feature_flag_definition_requests():
         client.load_feature_flags()
 
     assert get.call_args.kwargs["headers"]["User-Agent"] == (
-        f"posthog-python-mcp/{MCP_VERSION}"
+        f"posthog-python-mcp/{VERSION}"
     )
     client.shutdown()
 
@@ -144,7 +144,7 @@ def test_mcp_library_identity_reaches_remote_config_requests():
         assert client.get_remote_config_payload("flag-key") == "payload"
 
     assert get.call_args.kwargs["headers"]["User-Agent"] == (
-        f"posthog-python-mcp/{MCP_VERSION}"
+        f"posthog-python-mcp/{VERSION}"
     )