LangGraph API Cheat Sheet

This quick reference guide summarizes the core API methods when building state machines with LangGraph.

1. Graph Setup Operators Reference

2. Shared State Annotation Declaration

Use Annotation.Root to declare properties and reducer logic:

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

const StateAnnotation = Annotation.Root({
  messages: Annotation<any[]>({
    reducer: (current, update) => current.concat(update),
    default: () => [],
  }),
  isApproved: Annotation<boolean>(),
});

3. Human-in-the-Loop API Reference

• interruptBefore: Compile option key to halt execution before a node runs.

const app = workflow.compile({ checkpointer, interruptBefore: ["nodeName"] });

• getState(config): Retrieve the state values at the active checkpoint.
• updateState(config, values): Modify the state values of a specific thread or checkpoint.
• getStateHistory(config): Load the list of all historical checkpoints stored for a thread.