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What are Workflows?

Workflows in LlamaIndex.TS provide an event-driven architecture for building complex agent systems. Instead of linear code execution, workflows:
  • React to events as they occur
  • Define handlers for different states
  • Enable stateful multi-step processes
  • Support parallel and conditional execution

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When to Use Workflows

  • Building complex agents with multiple decision points
  • Creating multi-agent systems with coordination
  • Implementing custom RAG patterns
  • Orchestrating long-running processes
  • Debugging and monitoring agent behavior

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Core Concepts

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Events

Events carry data between workflow steps: 
import { workflowEvent } from "@llamaindex/workflow";

// Define event types
const startEvent = workflowEvent<string>();
const processEvent = workflowEvent<{ data: string; score: number }>();
const resultEvent = workflowEvent<{ result: string }>();

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Handlers

Handlers process events and emit new ones: 
import { createWorkflow } from "@llamaindex/workflow";

const workflow = createWorkflow();

// Register handler for start event
workflow.handle([startEvent], async (context, event) => {
  const input = event.data;
  // Process input...
  return processEvent.with({ data: input, score: 0.9 });
});

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State Management

Maintain state across workflow steps: 
import { 
  createWorkflow, 
  createStatefulMiddleware 
} from "@llamaindex/workflow";

const { withState } = createStatefulMiddleware(() => ({
  numIterations: 0,
  maxIterations: 3
}));

const workflow = withState(createWorkflow());

workflow.handle([processEvent], async (context, event) => {
  context.state.numIterations++;
  
  if (context.state.numIterations < context.state.maxIterations) {
    // Continue processing
    return processEvent.with(event.data);
  }
  
  // Done
  return resultEvent.with({ result: "Complete" });
});

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Complete Working Example: Joke Generator

This example shows a workflow that iteratively improves a joke: 
import { openai } from "@llamaindex/openai";
import {
  createStatefulMiddleware,
  createWorkflow,
  workflowEvent
} from "@llamaindex/workflow";

// Create LLM
const llm = openai({ model: "gpt-4o-mini" });

// Define events
const startEvent = workflowEvent<string>();
const jokeEvent = workflowEvent<{ joke: string }>();
const critiqueEvent = workflowEvent<{ 
  joke: string; 
  critique: string 
}>();
const resultEvent = workflowEvent<{ 
  joke: string; 
  critique: string 
}>();

// Create stateful workflow
const { withState } = createStatefulMiddleware(() => ({
  numIterations: 0,
  maxIterations: 3
}));

const jokeFlow = withState(createWorkflow());

// Handler 1: Generate initial joke
jokeFlow.handle([startEvent], async (context, event) => {
  const prompt = `Write your best joke about ${event.data}. Write the joke between <joke> and </joke> tags.`;
  const response = await llm.complete({ prompt });
  
  const joke = response.text
    .match(/<joke>([\s\S]*?)<\/joke>/)?.[1]?.trim() 
    ?? response.text;
    
  return jokeEvent.with({ joke });
});

// Handler 2: Critique the joke
jokeFlow.handle([jokeEvent], async (context, event) => {
  const prompt = `Give a thorough critique of the following joke. If the joke needs improvement, put "IMPROVE" somewhere in the critique: ${event.data.joke}`;
  const response = await llm.complete({ prompt });
  
  // Check if improvement needed
  if (response.text.includes("IMPROVE")) {
    return critiqueEvent.with({
      joke: event.data.joke,
      critique: response.text
    });
  }
  
  // Joke is good enough
  return resultEvent.with({ 
    joke: event.data.joke, 
    critique: response.text 
  });
});

// Handler 3: Improve the joke
jokeFlow.handle([critiqueEvent], async (context, event) => {
  const state = context.state;
  state.numIterations++;
  
  const prompt = `Write a new joke based on the following critique and the original joke. Write the joke between <joke> and </joke> tags.\n\nJoke: ${event.data.joke}\n\nCritique: ${event.data.critique}`;
  const response = await llm.complete({ prompt });
  
  const joke = response.text
    .match(/<joke>([\s\S]*?)<\/joke>/)?.[1]?.trim() 
    ?? response.text;
  
  // Check iteration limit
  if (state.numIterations < state.maxIterations) {
    return jokeEvent.with({ joke });
  }
  
  return resultEvent.with({ 
    joke, 
    critique: event.data.critique 
  });
});

// Execute the workflow
async function main() {
  const { stream, sendEvent } = jokeFlow.createContext();
  sendEvent(startEvent.with("pirates"));
  
  let result;
  
  for await (const event of stream) {
    if (resultEvent.include(event)) {
      result = event.data;
      break;
    }
  }
  
  console.log("Final joke:", result?.joke);
  console.log("Critique:", result?.critique);
}

main().catch(console.error);

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Workflow Patterns

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Linear Pipeline

Sequential processing steps: 
const workflow = createWorkflow();

workflow.handle([inputEvent], async (context, event) => {
  const processed = await step1(event.data);
  return step2Event.with(processed);
});

workflow.handle([step2Event], async (context, event) => {
  const processed = await step2(event.data);
  return step3Event.with(processed);
});

workflow.handle([step3Event], async (context, event) => {
  const result = await step3(event.data);
  return resultEvent.with(result);
});

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Conditional Branching

Route events based on conditions: 
workflow.handle([inputEvent], async (context, event) => {
  const data = event.data;
  
  if (data.type === "A") {
    return pathAEvent.with(data);
  } else if (data.type === "B") {
    return pathBEvent.with(data);
  } else {
    return errorEvent.with({ error: "Unknown type" });
  }
});

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Looping with State

Iterate until a condition is met: 
const { withState } = createStatefulMiddleware(() => ({
  attempts: 0,
  maxAttempts: 5
}));

const workflow = withState(createWorkflow());

workflow.handle([processEvent], async (context, event) => {
  context.state.attempts++;
  
  const success = await tryOperation(event.data);
  
  if (success) {
    return successEvent.with(event.data);
  } else if (context.state.attempts < context.state.maxAttempts) {
    // Retry
    return processEvent.with(event.data);
  } else {
    return failureEvent.with({ 
      error: "Max attempts reached" 
    });
  }
});

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Parallel Processing

Handle multiple events simultaneously: 
workflow.handle([inputEvent], async (context, event) => {
  // Trigger multiple parallel paths
  return [
    taskAEvent.with(event.data),
    taskBEvent.with(event.data),
    taskCEvent.with(event.data)
  ];
});

// Collect results
workflow.handle(
  [taskAResultEvent, taskBResultEvent, taskCResultEvent],
  async (context, event) => {
    // Process when all tasks complete
    return finalEvent.with({
      results: [event.data]
    });
  }
);

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Event Streaming

Stream workflow events in real-time: 
const { stream, sendEvent } = workflow.createContext();
sendEvent(startEvent.with("input"));

for await (const event of stream) {
  if (progressEvent.include(event)) {
    console.log("Progress:", event.data.percentage);
  } else if (resultEvent.include(event)) {
    console.log("Result:", event.data);
    break;
  }
}

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Debugging Workflows

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Event Logging

Log all events for debugging: 
workflow.handle(["*"], async (context, event) => {
  console.log("Event:", event.type, event.data);
  // Don't emit new events in logging handler
});

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State Inspection

Access workflow state: 
workflow.handle([inspectEvent], async (context, event) => {
  console.log("Current state:", context.state);
  return continueEvent.with(event.data);
});

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Building Custom Agent Workflows

Workflows are the foundation for the agent() helper. You can build custom agent patterns: 
import { 
  agentInputEvent,
  agentOutputEvent,
  agentToolCallEvent,
  createWorkflow
} from "@llamaindex/workflow";

const customAgent = createWorkflow();

customAgent.handle([agentInputEvent], async (context, event) => {
  // Custom agent logic
  const response = await llm.chat({ messages: event.data.messages });
  
  if (response.toolCalls) {
    return agentToolCallEvent.with({ toolCalls: response.toolCalls });
  }
  
  return agentOutputEvent.with({ message: response.message });
});

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Next Steps

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