This error is raised in the prebuilt create_react_agent when the call_model graph node receives a malformed list of messages. Specifically, it is malformed when there are AIMessages with tool_calls (LLM requesting to call a tool) that do not have a corresponding ToolMessage (result of a tool invocation to return to the LLM).There could be a few reasons you’re seeing this error:
You manually passed a malformed list of messages when invoking the graph, e.g. graph.invoke({'messages': [AIMessage(..., tool_calls=[...])]})
The graph was interrupted before receiving updates from the tools node (i.e. a list of ToolMessages)
and you invoked it with an input that is not None or a ToolMessage,
e.g. graph.invoke({'messages': [HumanMessage(...)]}, config).
This interrupt could have been triggered in one of the following ways:
You manually set interrupt_before = ['tools'] in create_react_agent
One of the tools raised an error that wasn’t handled by the ToolNode ("tools")
Don’t invoke the graph with a malformed list of messages
In case of an interrupt (manual or due to an error) you can:
provide ToolMessages that match existing tool calls and call graph.invoke({'messages': [ToolMessage(...)]}).
NOTE: this will append the messages to the history and run the graph from the START node.
manually update the state and resume the graph from the interrupt:
get the list of most recent messages from the graph state with graph.get_state(config)
modify the list of messages to either remove unanswered tool calls from AIMessages
or add ToolMessages with tool_call_ids that match unanswered tool calls 3. call graph.update_state(config, {'messages': ...}) with the modified list of messages 4. resume the graph, e.g. call graph.invoke(None, config)