Python: MCP plugin for Realtime Agent

[vslepakov]

Hey folks,

I am trying to invoke an MCP plugin using the realtime agent and running into an issue.
Function calling seems to be working fine in this sample, then I tried adding an MCPStdioPlugin like so:

...
    async with MCPStdioPlugin(
        name="Github",
        description="Github Plugin get information about repositories, issues and pull requests.",
        command="npx",
        args=[
            "-y",
            "@modelcontextprotocol/server-github",
        ],
        env={"GITHUB_PERSONAL_ACCESS_TOKEN": os.getenv("GITHUB_PERSONAL_ACCESS_TOKEN")},
    ) as github_plugin:
        realtime_agent = AzureRealtimeWebsocket(plugins=[github_plugin])
...

and while I seem to be getting data:

the app crashes with:

File "/Users/vs/Projects/semantic-kernel/python/semantic_kernel/connectors/ai/open_ai/services/_open_ai_realtime.py", line 464, in _parse_function_call_arguments_done
await self.send(result)
File "/Users/vs/Projects/semantic-kernel/python/semantic_kernel/connectors/ai/open_ai/services/_open_ai_realtime.py", line 516, in send
_create_openai_realtime_client_event(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
event_type=SendEvents.CONVERSATION_ITEM_CREATE,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...<4 lines>...
},
^^
)
^
File "/Users/vs/Projects/semantic-kernel/python/semantic_kernel/connectors/ai/open_ai/services/_open_ai_realtime.py", line 192, in _create_openai_realtime_client_event
return ConversationItemCreateEvent(**kwargs)
File "/Users/vs/Projects/semantic-kernel/python/.venv/lib/python3.13/site-packages/pydantic/main.py", line 253, in init
validated_self = self.pydantic_validator.validate_python(data, self_instance=self)
pydantic_core._pydantic_core.ValidationError: 1 validation error for ConversationItemCreateEvent
item.output
Input should be a valid string [type=string_type, input_value=[TextContent(inner_conten... }\n]', encoding=None)], input_type=list]
For further information visit https://errors.pydantic.dev/2.11/v/string_type

Is this a supported scenario? If yes, what might be the reason for the error?

[moonbox3]

Hi @vslepakov, thanks for the question. I will need to look into this for you. To make sure I understand, the text attribute you're showing above is a list? Or a list of dict?

[vslepakov]

Hi @moonbox3, thanks for checking this out! The data is actually a list of objects (dicts) when converted to JSON, but it’s being returned (or it looks like so in the debugger) as a string (note the surrounding '[]'). It seems like some parsing logic in SK might be failing here.
MCP servers can return data in various shapes and forms, in the function calling examples only strings are returned.