langchain-ai/langchain · error · KeyError

Reference '{path}' not found.

Error message

Reference '{path}' not found.

What it means

Error "Reference '{path}' not found." thrown in langchain-ai/langchain.

Source

Thrown at libs/core/langchain_core/utils/json_schema.py:41

        A deep copy of the referenced object (dict or list).

    Raises:
        ValueError: If the path does not start with `'#'`.
        KeyError: If the reference path is not found in the schema.
    """
    components = path.split("/")
    if components[0] != "#":
        msg = (
            "ref paths are expected to be URI fragments, meaning they should start "
            "with #."
        )
        raise ValueError(msg)
    out: list[Any] | dict[Any, Any] = schema
    for component in components[1:]:
        if component in out:
            if isinstance(out, list):
                msg = f"Reference '{path}' not found."
                raise KeyError(msg)
            out = out[component]
        elif component.isdigit():
            index = int(component)
            if (isinstance(out, list) and 0 <= index < len(out)) or (
                isinstance(out, dict) and index in out
            ):
                out = out[index]
            else:
                msg = f"Reference '{path}' not found."
                raise KeyError(msg)
        else:
            msg = f"Reference '{path}' not found."
            raise KeyError(msg)
    return deepcopy(out)


def _process_dict_properties(
    properties: dict[str, Any],

View on GitHub (pinned to e32fa9a52e)

Solutions

1. Verify the '$ref' path points to an existing node in the schema (e.g. '#/definitions/X' requires a 'definitions' object containing 'X').
2. Inline the referenced subschema, or fix the schema so the referenced key exists.

Example fix

schema['definitions'] = {'MyModel': {...}}  # then '#/definitions/MyModel' resolves

When it happens

Trigger: Raised when a JSON Schema $ref fragment path points to a location that does not exist in the schema being dereferenced.

Common situations: See trigger scenarios.

AI-assisted analysis of langchain-ai/langchain@e32fa9a52e (2026-08-14). Data as JSON: /api/errors/df43e39dcd3f7605. Report an issue: GitHub.