> ## Documentation Index
> Fetch the complete documentation index at: https://langchain-5e9cc07a-preview-opensw-1782332329-96d87c7.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# INVALID_CHAT_HISTORY

This error is raised in the prebuilt [`create_agent`](https://reference.langchain.com/python/langchain/agents/factory/create_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`](https://reference.langchain.com/python/langchain-core/messages/tool/ToolMessage) (result of a tool invocation to return to the LLM).

There could be a few reasons you're seeing this error:

1. You manually passed a malformed list of messages when invoking the graph, e.g. `graph.invoke({'messages': [AIMessage(..., tool_calls=[...])]})`
2. The graph was interrupted before receiving updates from the `tools` node (i.e. a list of [`ToolMessage`](https://reference.langchain.com/python/langchain-core/messages/tool/ToolMessage))
   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_agent`
   * One of the tools raised an error that wasn't handled by the [`ToolNode`](https://reference.langchain.com/python/langgraph/agents/#langgraph.prebuilt.tool_node.ToolNode) (`"tools"`)

## Troubleshooting

To resolve this, you can do one of the following:

1. Don't invoke the graph with a malformed list of messages
2. In case of an interrupt (manual or due to an error) you can:

* provide [`ToolMessage`](https://reference.langchain.com/python/langchain-core/messages/tool/ToolMessage) objects 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:
    1. get the list of most recent messages from the graph state with `graph.get_state(config)`
    2. modify the list of messages to either remove unanswered tool calls from AIMessages

or add [`ToolMessage`](https://reference.langchain.com/python/langchain-core/messages/tool/ToolMessage) objects 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)`

***

<div className="source-links">
  <Callout icon="terminal-2">
    [Connect these docs](/use-these-docs) to Claude, VSCode, and more via MCP for real-time answers.
  </Callout>

  <Callout icon="edit">
    [Edit this page on GitHub](https://github.com/langchain-ai/docs/edit/main/src/oss/langgraph/errors/INVALID_CHAT_HISTORY.mdx) or [file an issue](https://github.com/langchain-ai/docs/issues/new/choose).
  </Callout>
</div>