langchain-ai/langgraph · error · InvalidModuleError

Refused to deserialize JSON constructor: {dotted}. No allowe

Error message

Refused to deserialize JSON constructor: {dotted}. No allowed_json_modules configured.

Unblock with ONE of:
  • JsonPlusSerializer(allowed_json_modules=[{needed!r}, ...])
  • (DANGEROUS) JsonPlusSerializer(allowed_json_modules=True)

Note: Prefix allowlists are intentionally unsupported; prefer exact symbols or plain-JSON representations revived without import-time side effects.

What it means

Error "Refused to deserialize JSON constructor: {dotted}. No allowed_json_modules configured. Unblock with ONE of: • JsonPlusSerializer(allowed_json_modules=[{needed!r}, ...]) • (DANGEROUS) JsonPlusSerializer(allowed_json_modules=True) Note: Prefix allowlists are intentionally unsupported; prefer exact symbols or plain-JSON representations revived without import-time side effects." thrown in langchain-ai/langgraph.

Source

Thrown at libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py:234

                "(legacy_method_field=%s, error=%s); returning None",
                ".".join((*module, name)),
                "method" in value,
                type(exc).__name__,
            )
            return None

    def _check_allowed_json_modules(self, value: dict[str, Any]) -> None:
        needed = tuple(value["id"])
        dotted = ".".join(needed)
        # Safe types (the same set already allowed for msgpack deserialization) are
        # permitted without an explicit allowlist — they are known-safe LangGraph and
        # LangChain types.  This restores backwards-compat for old "json" checkpoints
        # that pre-date the msgpack migration without reopening the broader security gate.
        if _is_safe_json_type(list(needed)):
            return

        if not self._allowed_json_modules:
            raise InvalidModuleError(
                f"Refused to deserialize JSON constructor: {dotted}. "
                "No allowed_json_modules configured.\n\n"
                "Unblock with ONE of:\n"
                f"  • JsonPlusSerializer(allowed_json_modules=[{needed!r}, ...])\n"
                "  • (DANGEROUS) JsonPlusSerializer(allowed_json_modules=True)\n\n"
                "Note: Prefix allowlists are intentionally unsupported; prefer exact symbols "
                "or plain-JSON representations revived without import-time side effects."
            )

        if self._allowed_json_modules is True:
            return
        if needed in self._allowed_json_modules:
            return

        raise InvalidModuleError(
            f"Refused to deserialize JSON constructor: {dotted}. "
            "Symbol is not in the deserialization allowlist.\n\n"
            "Add exactly this symbol to unblock:\n"

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py:234 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/db9d131010b8c252. Report an issue: GitHub.