langchain-ai/langgraph · error · ValueError

Already found path for node '{start_key}'. For multiple edge

Error message

Already found path for node '{start_key}'.
For multiple edges, use StateGraph with an Annotated state key.

What it means

Error "Already found path for node '{start_key}'. For multiple edges, use StateGraph with an Annotated state key." thrown in langchain-ai/langgraph.

Source

Thrown at libs/langgraph/langgraph/graph/state.py:961

            Self: The instance of the `StateGraph`, allowing for method chaining.
        """
        if self.compiled:
            logger.warning(
                "Adding an edge to a graph that has already been compiled. This will "
                "not be reflected in the compiled graph."
            )

        if isinstance(start_key, str):
            if start_key == END:
                raise ValueError("END cannot be a start node")
            if end_key == START:
                raise ValueError("START cannot be an end node")

            # run this validation only for non-StateGraph graphs
            if not hasattr(self, "channels") and start_key in set(
                start for start, _ in self.edges
            ):
                raise ValueError(
                    f"Already found path for node '{start_key}'.\n"
                    "For multiple edges, use StateGraph with an Annotated state key."
                )

            self.edges.add((start_key, end_key))
            return self

        for start in start_key:
            if start == END:
                raise ValueError("END cannot be a start node")
            if start not in self.nodes:
                raise ValueError(f"Need to add_node `{start}` first")
        if end_key == START:
            raise ValueError("START cannot be an end node")
        if end_key != END and end_key not in self.nodes:
            raise ValueError(f"Need to add_node `{end_key}` first")

        self.waiting_edges.add((tuple(start_key), end_key))

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/langgraph/langgraph/graph/state.py:961 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/96ba015da226c7dc. Report an issue: GitHub.