human-in-the-loop

Human-in-the-loop

To review, edit and approve tool calls in an agent you can use LangGraph's built-in human-in-the-loop features, specifically the interrupt() primitive.

LangGraph allows you to pause execution indefinitely — for minutes, hours, or even days—until human input is received.

This is possible because the agent state is checkpointed into a database, which allows the system to persist execution context and later resume the workflow, continuing from where it left off.

For a deeper dive into the human-in-the-loop concept, see the concept guide.

Review tool calls

To add a human approval step to a tool:

1. Use interrupt() in the tool to pause execution.
2. Resume with a Command({ resume: ... }) to continue based on human input.

import { MemorySaver } from "@langchain/langgraph-checkpoint";
import { interrupt } from "@langchain/langgraph";
import { createReactAgent } from "@langchain/langgraph/prebuilt";
import { initChatModel } from "langchain/chat_models/universal";
import { tool } from "@langchain/core/tools";
import { z } from "zod";

// An example of a sensitive tool that requires human review / approval
const bookHotel = tool(
  async (input: { hotelName: string; }) => {
    let hotelName = input.hotelName;
    // highlight-next-line
    const response = interrupt(  // (1)!
      `Trying to call \`book_hotel\` with args {'hotel_name': ${hotelName}}. ` +
      `Please approve or suggest edits.`
    )
    if (response.type === "accept") {
      // proceed to execute the tool logic
    } else if (response.type === "edit") {
        hotelName = response.args["hotel_name"]
    } else {
        throw new Error(`Unknown response type: ${response.type}`)
    }
    return `Successfully booked a stay at ${hotelName}.`;
  },
  {
    name: "bookHotel",
    schema: z.object({
      hotelName: z.string().describe("Hotel to book"),
    }),
    description: "Book a hotel.",
  }
);

// highlight-next-line
const checkpointer = new MemorySaver();  // (2)!

const llm = await initChatModel("anthropic:claude-3-7-sonnet-latest");
const agent = createReactAgent({
  llm,
  tools: [bookHotel],
  // highlight-next-line
  checkpointer  // (3)!
});