langchain-ai/langgraph · error · ValueError

Key {chan} not in channels

Error message

Key {chan} not in channels

What it means

Error "Key {chan} not in channels" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/pregel/_validate.py:120

            if n not in nodes:
                raise ValueError(f"Node {n} not in nodes")
    if interrupt_before_nodes != "*":
        for n in interrupt_before_nodes:
            if n not in nodes:
                raise ValueError(f"Node {n} not in nodes")


def validate_keys(
    keys: str | Sequence[str] | None,
    channels: Mapping[str, Any],
) -> None:
    if isinstance(keys, str):
        if keys not in channels:
            raise ValueError(f"Key {keys} not in channels")
    elif keys is not None:
        for chan in keys:
            if chan not in channels:
                raise ValueError(f"Key {chan} not in channels")

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/pregel/_validate.py:120 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/f18b4992f4e22b90. Report an issue: GitHub.