langchain/tools/base.py/Tool/_to_args_and_kwargs
class Tool:    def _to_args_and_kwargs(self, tool_input: Union[str, Dict]) -> Tuple[Tuple, Dict]:
        """Convert tool input to pydantic model."""
        args, kwargs = super()._to_args_and_kwargs(tool_input)
        # For backwards compatibility. The tool must be run with a single input
        all_args = list(args) + list(kwargs.values())
        if len(all_args) != 1:
            raise ValueError(
                f"Too many arguments to single-input tool {self.name}."
                f" Args: {all_args}"
            )
        return tuple(all_args), {}