microsoft/autogen · error · ToolNotFoundException

Error: Tool not found: {message.name}

Error message

Error: Tool not found: {message.name}

What it means

Error "Error: Tool not found: {message.name}" thrown in microsoft/autogen.

Source

Thrown at python/packages/autogen-core/src/autogen_core/tool_agent/_tool_agent.py:80

    @message_handler
    async def handle_function_call(self, message: FunctionCall, ctx: MessageContext) -> FunctionExecutionResult:
        """Handles a `FunctionCall` message by executing the requested tool with the provided arguments.

        Args:
            message (FunctionCall): The function call message.
            cancellation_token (CancellationToken): The cancellation token.

        Returns:
            FunctionExecutionResult: The result of the function execution.

        Raises:
            ToolNotFoundException: If the tool is not found.
            InvalidToolArgumentsException: If the tool arguments are invalid.
            ToolExecutionException: If the tool execution fails.
        """
        tool = next((tool for tool in self._tools if tool.name == message.name), None)
        if tool is None:
            raise ToolNotFoundException(
                call_id=message.id, content=f"Error: Tool not found: {message.name}", name=message.name
            )
        else:
            try:
                arguments = json.loads(message.arguments)
                result = await tool.run_json(
                    args=arguments, cancellation_token=ctx.cancellation_token, call_id=message.id
                )
                result_as_str = tool.return_value_as_string(result)
            except json.JSONDecodeError as e:
                raise InvalidToolArgumentsException(
                    call_id=message.id, content=f"Error: Invalid arguments: {message.arguments}", name=message.name
                ) from e
            except Exception as e:
                raise ToolExecutionException(call_id=message.id, content=f"Error: {e}", name=message.name) from e
        return FunctionExecutionResult(content=result_as_str, call_id=message.id, is_error=False, name=message.name)

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Register the tool or correct the tool name in the call

Example fix

Add the tool to the ToolAgent's tools list

When it happens

Trigger: Thrown at python/packages/autogen-core/src/autogen_core/tool_agent/_tool_agent.py:80 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/85eed59cb93cabd2. Report an issue: GitHub.