langchain-ai/langgraph · error · ValueError

A tool argument should not be annotated with {injection_type

Error message

A tool argument should not be annotated with {injection_type.__name__} more than once. Found: {matches}

What it means

Error "A tool argument should not be annotated with {injection_type.__name__} more than once. Found: {matches}" thrown in langchain-ai/langgraph.

Source

Thrown at libs/prebuilt/langgraph/prebuilt/tool_node.py:1957

) -> Any | None:
    """Extract injection instance from a type annotation.

    Args:
        type_: The type annotation to check.
        injection_type: The injection type to look for.

    Returns:
        The injection instance if found, True if injection marker found without instance, None otherwise.
    """
    type_args = get_args(type_)
    matches = [arg for arg in type_args if _is_injection(arg, injection_type)]

    if len(matches) > 1:
        msg = (
            f"A tool argument should not be annotated with {injection_type.__name__} "
            f"more than once. Found: {matches}"
        )
        raise ValueError(msg)

    if len(matches) == 1:
        return matches[0]
    elif _is_injection(type_, injection_type):
        return True

    return None


def _get_all_injected_args(tool: BaseTool) -> _InjectedArgs:
    """Extract all injected arguments from tool in a single pass.

    This function analyzes both the tool's input schema and function signature
    to identify all arguments that should be injected (state, store, runtime).

    Args:
        tool: The tool to analyze for injection requirements.

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/prebuilt/langgraph/prebuilt/tool_node.py:1957 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/e725e5b636c97fee. Report an issue: GitHub.