langchain-ai/langgraph · error · ValueError

Input channel '{chan}' not in '{repr(sorted(channels))[:100]

Error message

Input channel '{chan}' not in '{repr(sorted(channels))[:100]}'

What it means

Error "Input channel '{chan}' not in '{repr(sorted(channels))[:100]}'" thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/pregel/_validate.py:78

    if isinstance(input_channels, str):
        if input_channels not in channels:
            raise ValueError(
                f"Input channel '{input_channels}' not "
                f"in known channels: '{repr(sorted(channels))[:100]}'"
            )
        if input_channels not in subscribed_channels:
            raise ValueError(
                f"Input channel {input_channels} is not subscribed to by any node"
            )
    else:
        for chan in input_channels:
            if chan not in channels:
                raise ValueError(
                    f"Input channel '{chan}' not in '{repr(sorted(channels))[:100]}'"
                )
        if all(chan not in subscribed_channels for chan in input_channels):
            raise ValueError(
                f"None of the input channels {input_channels} "
                f"are subscribed to by any node"
            )

    all_output_channels = set[str]()
    if isinstance(output_channels, str):
        all_output_channels.add(output_channels)
    else:
        all_output_channels.update(output_channels)
    if isinstance(stream_channels, str):
        all_output_channels.add(stream_channels)
    elif stream_channels is not None:
        all_output_channels.update(stream_channels)

    for chan in all_output_channels:
        if chan not in channels:
            raise ValueError(
                f"Output channel '{chan}' not "

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/pregel/_validate.py:78 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/3d42cdda6f6a3c3e. Report an issue: GitHub.