INVALID_TOOL_RESULTS

Currently only used in `langchainjs` (JavaScript/TypeScript).

This error occurs when passing mismatched, insufficient, or excessive @[ToolMessage] objects to a model during tool calling operations.

The error stems from a fundamental requirement: an assistant message with tool_calls must be followed by tool messages responding to each tool_call_id.

When a model returns an @[AIMessage] with tool calls, you must provide exactly one corresponding @[ToolMessage] for each tool call, with matching tool_call_id values.

Common causes

• Insufficient responses: If a model requests two tool executions but you only provide one response message, the model rejects the incomplete message chain
• Duplicate responses: Providing multiple @[ToolMessage] objects for the same tool call ID results in rejection, as does having unmatched IDs
• Orphaned tool messages: Sending a @[ToolMessage] without a preceding @[AIMessage] containing tool calls violates protocol requirements

Here's an example of a problematic pattern:

# Model requests two tool calls
response_message.tool_calls  # Returns 2 calls
 
# But only one ToolMessage provided
chat_history.append(ToolMessage(
    content=str(tool_response),
    tool_call_id=tool_call.get("id")
))
 
model_with_tools.invoke(chat_history)

Troubleshooting

To resolve this error:

• Count matching pairs: Ensure one @[ToolMessage] exists per tool call in the preceding @[AIMessage]
• Verify IDs: Confirm each ToolMessage.tool_call_id matches an actual tool call identifier