langchain-ai/langgraph · error · ValueError

No AIMessage found in input

Error message

No AIMessage found in input

What it means

Error "No AIMessage found in input" thrown in langchain-ai/langgraph.

Source

Thrown at libs/prebuilt/langgraph/prebuilt/tool_node.py:1263

            return [input_with_ctx["tool_call"]], input_type
        elif isinstance(input, dict) and (
            messages := input.get(self._messages_key, [])
        ):
            input_type = "dict"
        elif messages := getattr(input, self._messages_key, []):
            # Assume dataclass-like state that can coerce from dict
            input_type = "dict"
        else:
            msg = "No message found in input"
            raise ValueError(msg)

        try:
            latest_ai_message = next(
                m for m in reversed(messages) if isinstance(m, AIMessage)
            )
        except StopIteration:
            msg = "No AIMessage found in input"
            raise ValueError(msg)

        tool_calls = list(latest_ai_message.tool_calls)
        return tool_calls, input_type

    def _validate_tool_call(self, call: ToolCall) -> ToolMessage | None:
        requested_tool = call["name"]
        if requested_tool not in self.tools_by_name:
            all_tool_names = list(self.tools_by_name.keys())
            content = INVALID_TOOL_NAME_ERROR_TEMPLATE.format(
                requested_tool=requested_tool,
                available_tools=", ".join(all_tool_names),
            )
            return ToolMessage(
                content, name=requested_tool, tool_call_id=call["id"], status="error"
            )
        return None

    def _extract_state(

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/prebuilt/langgraph/prebuilt/tool_node.py:1263 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/e7cbf5622d93a66e. Report an issue: GitHub.