---
title: Human-in-the-Loop Workflows | Developer Documentation
description: Learn how to build human-in-the-loop workflows
---

LlamaIndex workflows support human-in-the-loop patterns where a workflow can pause, wait for human input, and then resume after the human input is received. This is useful for scenarios like:

- Getting user approval for actions
- Collecting additional information from users

For this to work, you need to use the `withState` middleware, which allows you to save the state of the workflow using the `snapshot` function and to resume the workflow from a saved snapshot using the `resume` function.

## Basic Human-in-the-Loop Pattern

Here’s how to implement a workflow that pauses for human input:

```
import { createWorkflow, workflowEvent } from "@llamaindex/workflow-core";
import { createStatefulMiddleware } from "@llamaindex/workflow-core/middleware/state";


// Define events
const startEvent = workflowEvent<string>();
const humanRequestEvent = workflowEvent<void>();
const humanResponseEvent = workflowEvent<string>();
const stopEvent = workflowEvent<string>();


const { withState } = createStatefulMiddleware(() => ({}));
const workflow = withState(createWorkflow());


// Workflow that needs human input
workflow.handle([startEvent], () => {
  return humanRequestEvent.with();
});


workflow.handle([humanResponseEvent], (context, event) => {
  return stopEvent.with(`Human said: ${event.data}`);
});


// Usage with snapshot/resume
const { sendEvent, snapshot, stream } = workflow.createContext();
sendEvent(startEvent.with("begin"));


// Wait for a human request and take a snapshot
await stream.until(humanRequestEvent).toArray();
const snapshotData = await snapshot();


// Later (in another request): resume and provide human input
const resumedContext = workflow.resume(snapshotData);
resumedContext.sendEvent(humanResponseEvent.with("hello world"));


const events = await resumedContext.stream.until(stopEvent).toArray();
console.log(events[events.length - 1].data); // "Human said: hello world"
```