microsoft/autogen · error · ValueError

Unsupported server params type: {type(server_params)}

Error message

Unsupported server params type: {type(server_params)}

What it means

The MCP tool factory builds adapters by isinstance-dispatch on the server params: StdioServerParams, SseServerParams, or StreamableHttpServerParams. Any other type — including duck-typed lookalikes, protocol re-exports from different package versions, or None — falls through to ValueError(f'Unsupported server params type: {type(server_params)}').

Source

Thrown at python/packages/autogen-ext/src/autogen_ext/tools/mcp/_factory.py:214

    """
    if session is None:
        async with create_mcp_server_session(server_params) as temp_session:
            await temp_session.initialize()

            tools = await temp_session.list_tools()
    else:
        tools = await session.list_tools()

    if isinstance(server_params, StdioServerParams):
        return [StdioMcpToolAdapter(server_params=server_params, tool=tool, session=session) for tool in tools.tools]
    elif isinstance(server_params, SseServerParams):
        return [SseMcpToolAdapter(server_params=server_params, tool=tool, session=session) for tool in tools.tools]
    elif isinstance(server_params, StreamableHttpServerParams):
        return [
            StreamableHttpMcpToolAdapter(server_params=server_params, tool=tool, session=session)
            for tool in tools.tools
        ]
    raise ValueError(f"Unsupported server params type: {type(server_params)}")

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Construct params using the classes autogen-ext itself re-exports (e.g. from autogen_ext.tools.mcp import StdioServerParams).
2. Print type(server_params) and its module path; if it is not from the expected mcp package, fix the import to use the same distribution autogen-ext depends on.
3. Resolve dependency conflicts: pip check / uv pip list, ensure a single mcp version, reinstall autogen-ext[mcp].
4. Do not pass None or raw dicts — build one of the three supported param objects.

Example fix

# before
from some_old_sdk import StdioServerParams  # different class identity

params = StdioServerParams(command="npx", args=["-y", "server"])
tools = await make_tools(params)  # ValueError: Unsupported server params type

# after
from autogen_ext.tools.mcp import StdioServerParams

params = StdioServerParams(command="npx", args=["-y", "@modelcontextprotocol/server"])
tools = await make_tools(params)

from autogen_ext.tools.mcp import StdioServerParams, SseServerParams, StreamableHttpServerParams

if not isinstance(server_params, (StdioServerParams, SseServerParams, StreamableHttpServerParams)):
    raise TypeError(f"unsupported params {type(server_params)!r}; use autogen_ext.tools.mcp param classes")

from autogen_ext.tools.mcp import StdioServerParams, SseServerParams, StreamableHttpServerParams
from typing import Any, TypeGuard, Union

SupportedParams = Union[StdioServerParams, SseServerParams, StreamableHttpServerParams]

def is_supported_server_params(p: Any) -> TypeGuard[SupportedParams]:
    return isinstance(p, (StdioServerParams, SseServerParams, StreamableHttpServerParams))

try:
    tools = await make_tools(server_params)
except ValueError as e:
    if "Unsupported server params type" in str(e):
        raise TypeError("Import param classes from autogen_ext.tools.mcp") from e
    raise

When it happens

Trigger: Passing an object that is not one of the three supported param classes: a mcp-types class imported from a different (incompatible) mcp package version so isinstance fails; a custom dataclass mimicking the shape; forgetting to construct params and passing the class itself or None.

Common situations: Two copies of the mcp package installed (plugin vs app) so the class identities differ; upgrading mcp to a version whose StdioServerParams moved modules while autogen-ext pins the old one; passing SseParams from a vendored SDK.

Related errors

• Failed to list MCP tools
• Failed to call MCP tool
• MCP health check failed
• HTTP ${response.status}: ${errorText || "Failed to create We
• Invalid JSON response from server. Check if the MCP route is

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/e0300b33a59ae481. Report an issue: GitHub.