microsoft/autogen · error · ValueError

Unsupported tool type: {type(tool)}

Error message

Unsupported tool type: {type(tool)}

What it means

AssistantAgent iterates over the tools argument and accepts only autogen_core.tools.BaseTool instances or plain Python callables (wrapped into FunctionTool using their docstring as description). Any other object raises ValueError with its type.

Source

Thrown at python/packages/autogen-agentchat/src/autogen_agentchat/agents/_assistant_agent.py:785

        if system_message is None:
            self._system_messages = []
        else:
            self._system_messages = [SystemMessage(content=system_message)]
        self._tools: List[BaseTool[Any, Any]] = []
        if tools is not None:
            if model_client.model_info["function_calling"] is False:
                raise ValueError("The model does not support function calling.")
            for tool in tools:
                if isinstance(tool, BaseTool):
                    self._tools.append(tool)
                elif callable(tool):
                    if hasattr(tool, "__doc__") and tool.__doc__ is not None:
                        description = tool.__doc__
                    else:
                        description = ""
                    self._tools.append(FunctionTool(tool, description=description))
                else:
                    raise ValueError(f"Unsupported tool type: {type(tool)}")
        # Check if tool names are unique.
        tool_names = [tool.name for tool in self._tools]
        if len(tool_names) != len(set(tool_names)):
            raise ValueError(f"Tool names must be unique: {tool_names}")

        # Handoff tools.
        self._handoff_tools: List[BaseTool[Any, Any]] = []
        self._handoffs: Dict[str, HandoffBase] = {}
        if handoffs is not None:
            if model_client.model_info["function_calling"] is False:
                raise ValueError("The model does not support function calling, which is needed for handoffs.")
            for handoff in handoffs:
                if isinstance(handoff, str):
                    handoff = HandoffBase(target=handoff)
                if isinstance(handoff, HandoffBase):
                    self._handoff_tools.append(handoff.handoff_tool)
                    self._handoffs[handoff.name] = handoff
                else:

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Ensure each item is a BaseTool instance or a plain function/lambda (callable).
2. Instantiate tool classes: MyTool() not MyTool.
3. Check for conflicting autogen-core installations (`pip list | grep autogen`) — tools defined against a different installed copy fail isinstance.

Example fix

# before
agent = AssistantAgent(name="a", model_client=client, tools=[MyTool])

# after
agent = AssistantAgent(name="a", model_client=client, tools=[MyTool()])

from autogen_core.tools import BaseTool
for t in tools:
    if not (isinstance(t, BaseTool) or callable(t)):
        raise ValueError(f"Unsupported tool entry: {t!r} ({type(t).__name__})")

from autogen_core.tools import BaseTool

def is_valid_tool(t) -> bool:
    return isinstance(t, BaseTool) or callable(t)

try:
    agent = AssistantAgent(name="a", model_client=client, tools=tools)
except ValueError as e:
    if "Unsupported tool type" in str(e):
        tools = [FunctionTool(t, name=t.__name__, description=t.__doc__ or "") if callable(t) else t for t in tools]
    else:
        raise

When it happens

Trigger: Passing a class (not an instance), a string tool name, a dict describing a tool, a Mock in tests, or an object from an incompatible autogen version whose BaseTool base class differs (isinstance fails across mismatched package copies).

Common situations: Copy-pasting tool definitions from other frameworks (Langchain tools, plain specs), duplicate autogen-core installs in the environment making isinstance checks fail, or forgetting to instantiate a tool class.

Related errors

• Expected Memory, List[Memory], or None, got {type(memory)}
• The model does not support function calling.
• Tool names must be unique: {tool_names}
• Unsupported handoff type: {type(handoff)}
• Handoff names must be unique from tool names

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/811dbc9073d44726. Report an issue: GitHub.