langchain-ai/langgraph · error · ValueError

Got unexpected type for `prompt`: {type}

Error message

Got unexpected type for `prompt`: {type}

What it means

Error "Got unexpected type for `prompt`: {type}" thrown in langchain-ai/langgraph.

Source

Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:168

        prompt_runnable = RunnableCallable(
            lambda state: [prompt] + _get_state_value(state, "messages"),
            name=PROMPT_RUNNABLE_NAME,
        )
    elif inspect.iscoroutinefunction(prompt):
        prompt_runnable = RunnableCallable(
            None,
            prompt,
            name=PROMPT_RUNNABLE_NAME,
        )
    elif callable(prompt):
        prompt_runnable = RunnableCallable(
            prompt,
            name=PROMPT_RUNNABLE_NAME,
        )
    elif isinstance(prompt, Runnable):
        prompt_runnable = prompt
    else:
        raise ValueError(f"Got unexpected type for `prompt`: {type(prompt)}")

    return prompt_runnable


def _should_bind_tools(
    model: LanguageModelLike, tools: Sequence[BaseTool], num_builtin: int = 0
) -> bool:
    if isinstance(model, RunnableSequence):
        model = next(
            (
                step
                for step in model.steps
                if isinstance(step, (RunnableBinding, BaseChatModel))
            ),
            model,
        )

    if not isinstance(model, RunnableBinding):

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/prebuilt/langgraph/prebuilt/chat_agent_executor.py:168 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/1f9fd09548a59f9e. Report an issue: GitHub.