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"