langchain-ai/langgraph · error · ValueError

Number of tools in the model.bind_tools() and tools passed t

Error message

Number of tools in the model.bind_tools() and tools passed to create_react_agent must match Got {len(tools)} tools, expected {len(bound_tools) - num_builtin}

What it means

Error "Number of tools in the model.bind_tools() and tools passed to create_react_agent must match Got {len(tools)} tools, expected {len(bound_tools) - num_builtin}" thrown in langchain-ai/langgraph.

Source

Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:194

    if isinstance(model, RunnableSequence):
        model = next(
            (
                step
                for step in model.steps
                if isinstance(step, (RunnableBinding, BaseChatModel))
            ),
            model,
        )

    if not isinstance(model, RunnableBinding):
        return True

    if "tools" not in model.kwargs:
        return True

    bound_tools = model.kwargs["tools"]
    if len(tools) != len(bound_tools) - num_builtin:
        raise ValueError(
            "Number of tools in the model.bind_tools() and tools passed to create_react_agent must match"
            f" Got {len(tools)} tools, expected {len(bound_tools) - num_builtin}"
        )

    tool_names = set(tool.name for tool in tools)
    bound_tool_names = set()
    for bound_tool in bound_tools:
        # OpenAI-style tool
        if bound_tool.get("type") == "function":
            bound_tool_name = bound_tool["function"]["name"]
        # Anthropic-style tool
        elif bound_tool.get("name"):
            bound_tool_name = bound_tool["name"]
        else:
            # unknown tool type so we'll ignore it
            continue

        bound_tool_names.add(bound_tool_name)

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:194 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/c62e3d064285de2b. Report an issue: GitHub.