UNREACHABLE_NODE

LangGraph cannot identify an incoming edge to one of your nodes. Check to ensure you have added sufficient edges when constructing your graph.

Alternatively, if you are returning Command instances from your nodes to make your graphs edgeless, you will need to add an additional ends parameter when calling addNode to help LangGraph determine the destinations for your node.

Here's an example:

import { Annotation, Command } from "@langchain/langgraph";

const StateAnnotation = Annotation.Root({
  foo: Annotation<string>,
});

const nodeA = async (_state: typeof StateAnnotation.State) => {
  const goto = Math.random() > .5 ? "nodeB" : "nodeC";
  return new Command({
    update: { foo: "a" },
    goto,
  });
};

const nodeB = async (state: typeof StateAnnotation.State) => {
  return {
    foo: state.foo + "|b",
  };
}

const nodeC = async (state: typeof StateAnnotation.State) => {
  return {
    foo: state.foo + "|c",
  };
}

import { StateGraph } from "@langchain/langgraph";

// NOTE: there are no edges between nodes A, B and C!
const graph = new StateGraph(StateAnnotation)
  .addNode("nodeA", nodeA, {
    // Explicitly specify "nodeB" and "nodeC" as potential destinations for nodeA
    ends: ["nodeB", "nodeC"],
  })
  .addNode("nodeB", nodeB)
  .addNode("nodeC", nodeC)
  .addEdge("__start__", "nodeA")
  .compile();

Troubleshooting

The following may help resolve this error:

• Make sure that you have not forgotten to add edges between some of your nodes.
• If you are returning Commands from your nodes, make sure that you're passing an ends array with the names of potential destination nodes as shown above.