Langgraph Workflows

langgraph-workflows (JavaScript/TypeScript)

name: langgraph-workflows description: Understanding workflows vs agents, predetermined vs dynamic patterns, and orchestrator-worker patterns using the Send API

Overview

LangGraph supports both workflows (predetermined paths) and agents (dynamic decision-making). Understanding when to use each pattern is crucial for effective agent design.

Key Distinctions:

• Workflows: Predetermined code paths, operate in specific order
• Agents: Dynamic, define their own processes and tool usage
• Hybrid: Combine deterministic and agentic steps

Decision Table: Workflow vs Agent

Key Patterns

1. Predetermined Workflows

Sequential execution with fixed paths:

• Data processing pipelines
• Validation workflows
• Multi-step transformations

2. Dynamic Agents

Model decides next steps:

• ReAct agents (reasoning + acting)
• Tool-calling loops
• Autonomous task completion

3. Orchestrator-Worker Pattern

One coordinator delegates to multiple workers:

• Map-reduce operations
• Parallel processing
• Multi-agent collaboration

Code Examples

Basic Workflow (Predetermined)

import { StateGraph, StateSchema, START, END } from "@langchain/langgraph";
import { z } from "zod";

const WorkflowState = new StateSchema({
  data: z.string(),
  validated: z.boolean(),
  processed: z.boolean(),
});

const validate = async (state: typeof WorkflowState.State) => {
  const isValid = state.data.length > 0;
  return { validated: isValid };
};

const process = async (state: typeof WorkflowState.State) => {
  return {
    data: state.data.toUpperCase(),
    processed: true,
  };
};

// Fixed workflow: validate → process
const workflow = new StateGraph(WorkflowState)
  .addNode("validate", validate)
  .addNode("process", process)
  .addEdge(START, "validate")
  .addEdge("validate", "process")  // Always go to process
  .addEdge("process", END)
  .compile();

const result = await workflow.invoke({ data: "hello" });
console.log(result);  // { data: 'HELLO', validated: true, processed: true }

Dynamic Agent (Model-Driven)

import { ChatAnthropic } from "@langchain/anthropic";
import { tool } from "@langchain/core/tools";
import { AIMessage, ToolMessage } from "@langchain/core/messages";
import { StateGraph, StateSchema, MessagesValue, END, START } from "@langchain/langgraph";
import { z } from "zod";

const search = tool(async ({ query }) => `Results for: ${query}`, {
  name: "search",
  description: "Search for information",
  schema: z.object({ query: z.string() }),
});

const calculate = tool(async ({ expression }) => eval(expression).toString(), {
  name: "calculate",
  description: "Calculate a mathematical expression",
  schema: z.object({ expression: z.string() }),
});

const AgentState = new StateSchema({
  messages: MessagesValue,
});

const model = new ChatAnthropic({ model: "claude-sonnet-4-5-20250929" });
const tools = [search, calculate];
const modelWithTools = model.bindTools(tools);

const agentNode = async (state: typeof AgentState.State) => {
  const response = await modelWithTools.invoke(state.messages);
  return { messages: [response] };
};

const toolNode = async (state: typeof AgentState.State) => {
  const lastMessage = state.messages.at(-1);
  if (!lastMessage || !AIMessage.isInstance(lastMessage)) {
    return { messages: [] };
  }

  const toolsByName = { [search.name]: search, [calculate.name]: calculate };
  const result = [];

  for (const toolCall of lastMessage.tool_calls ?? []) {
    const tool = toolsByName[toolCall.name];
    const observation = await tool.invoke(toolCall);
    result.push(observation);
  }

  return { messages: result };
};

const shouldContinue = (state: typeof AgentState.State) => {
  const lastMessage = state.messages.at(-1);
  if (lastMessage && AIMessage.isInstance(lastMessage) && lastMessage.tool_calls?.length) {
    return "tools";
  }
  return END;
};

// Dynamic agent: model decides when to stop
const agent = new StateGraph(AgentState)
  .addNode("agent", agentNode)
  .addNode("tools", toolNode)
  .addEdge(START, "agent")
  .addConditionalEdges("agent", shouldContinue, ["tools", END])
  .addEdge("tools", "agent")
  .compile();

Orchestrator-Worker Pattern

import { StateGraph, StateSchema, Send, ReducedValue, START, END } from "@langchain/langgraph";
import { z } from "zod";

const OrchestratorState = new StateSchema({
  tasks: z.array(z.string()),
  results: new ReducedValue(
    z.array(z.string()).default(() => []),
    { reducer: (current, update) => current.concat(update) }
  ),
  summary: z.string().optional(),
});

const orchestrator = (state: typeof OrchestratorState.State) => {
  // Fan out tasks to workers
  return state.tasks.map(task => new Send("worker", { task }));
};

const worker = async (state: { task: string }) => {
  const result = `Completed: ${state.task}`;
  return { results: [result] };
};

const synthesize = async (state: typeof OrchestratorState.State) => {
  const summary = `Processed ${state.results.length} tasks`;
  return { summary };
};

const graph = new StateGraph(OrchestratorState)
  .addNode("worker", worker)
  .addNode("synthesize", synthesize)
  .addConditionalEdges(START, orchestrator, ["worker"])
  .addEdge("worker", "synthesize")
  .addEdge("synthesize", END)
  .compile();

const result = await graph.invoke({
  tasks: ["Task A", "Task B", "Task C"],
});
console.log(result.summary);  // "Processed 3 tasks"

Hybrid: Workflow with Agent Step

import { StateGraph, StateSchema, START, END } from "@langchain/langgraph";
import { z } from "zod";

const HybridState = new StateSchema({
  input: z.string(),
  validated: z.boolean(),
  agentResponse: z.string().optional(),
  finalized: z.boolean(),
});

const validate = async (state: typeof HybridState.State) => {
  return { validated: true };
};

const agentProcess = async (state: typeof HybridState.State) => {
  // Dynamic agent logic here
  const response = `Agent processed: ${state.input}`;
  return { agentResponse: response };
};

const finalize = async (state: typeof HybridState.State) => {
  return { finalized: true };
};

// Hybrid: validate → agent → finalize
const hybrid = new StateGraph(HybridState)
  .addNode("validate", validate)      // Workflow
  .addNode("agent", agentProcess)     // Agent
  .addNode("finalize", finalize)      // Workflow
  .addEdge(START, "validate")
  .addEdge("validate", "agent")
  .addEdge("agent", "finalize")
  .addEdge("finalize", END)
  .compile();

Map-Reduce Example

import { StateGraph, StateSchema, Send, ReducedValue, START, END } from "@langchain/langgraph";
import { z } from "zod";

const MapReduceState = new StateSchema({
  documents: z.array(z.string()),
  summaries: new ReducedValue(
    z.array(z.string()).default(() => []),
    { reducer: (current, update) => current.concat(update) }
  ),
  finalSummary: z.string().optional(),
});

const mapDocuments = (state: typeof MapReduceState.State) => {
  return state.documents.map(doc => new Send("summarize", { doc }));
};

const summarize = async (state: { doc: string }) => {
  const summary = `Summary of: ${state.doc.slice(0, 50)}...`;
  return { summaries: [summary] };
};

const reduce = async (state: typeof MapReduceState.State) => {
  const finalSummary = state.summaries.join(" | ");
  return { finalSummary };
};

const graph = new StateGraph(MapReduceState)
  .addNode("summarize", summarize)
  .addNode("reduce", reduce)
  .addConditionalEdges(START, mapDocuments, ["summarize"])
  .addEdge("summarize", "reduce")
  .addEdge("reduce", END)
  .compile();

const result = await graph.invoke({
  documents: ["Doc 1 content...", "Doc 2 content...", "Doc 3 content..."],
});

Parallel Knowledge Base Router

import { StateGraph, StateSchema, Send, ReducedValue, START, END } from "@langchain/langgraph";
import { z } from "zod";

const RouterState = new StateSchema({
  query: z.string(),
  sources: z.array(z.string()),
  results: new ReducedValue(
    z.array(z.string()).default(() => []),
    { reducer: (current, update) => current.concat(update) }
  ),
  final: z.string().optional(),
});

const classify = async (state: typeof RouterState.State) => {
  const query = state.query.toLowerCase();
  const sources: string[] = [];

  if (query.includes("code")) sources.push("github");
  if (query.includes("doc")) sources.push("notion");
  if (query.includes("message")) sources.push("slack");

  return { sources };
};

const routeToSources = (state: typeof RouterState.State) => {
  return state.sources.map(source => new Send(source, { query: state.query }));
};

const queryGithub = async (state: { query: string }) => {
  return { results: [`GitHub: ${state.query}`] };
};

const queryNotion = async (state: { query: string }) => {
  return { results: [`Notion: ${state.query}`] };
};

const querySlack = async (state: { query: string }) => {
  return { results: [`Slack: ${state.query}`] };
};

const synthesize = async (state: typeof RouterState.State) => {
  return { final: state.results.join(" + ") };
};

const graph = new StateGraph(RouterState)
  .addNode("classify", classify)
  .addNode("github", queryGithub)
  .addNode("notion", queryNotion)
  .addNode("slack", querySlack)
  .addNode("synthesize", synthesize)
  .addEdge(START, "classify")
  .addConditionalEdges("classify", routeToSources, ["github", "notion", "slack"])
  .addEdge("github", "synthesize")
  .addEdge("notion", "synthesize")
  .addEdge("slack", "synthesize")
  .addEdge("synthesize", END)
  .compile();

Boundaries

What You CAN Configure

✅ Choose workflow vs agent pattern ✅ Mix deterministic and agentic steps ✅ Use Send API for parallel execution ✅ Define custom orchestrator logic ✅ Control worker node behavior ✅ Aggregate results with reducers

What You CANNOT Configure

❌ Change Send API message-passing model ❌ Bypass worker state isolation ❌ Modify parallel execution mechanism ❌ Override reducer behavior at runtime

Gotchas

1. Send Requires Worker State Isolation

// ❌ WRONG - Workers share state, causing conflicts
const State = new StateSchema({
  sharedCounter: z.number(),  // All workers modify same counter!
});

// ✅ CORRECT - Each worker gets isolated input
const worker = async (state: { task: string }) => {
  // state is isolated to this worker
  return { results: [process(state.task)] };
};

2. Send Needs Accumulator Reducer

// ❌ WRONG - Last worker overwrites all others
const State = new StateSchema({
  results: z.array(z.string()),  // No reducer!
});

// ✅ CORRECT - Use ReducedValue
import { ReducedValue } from "@langchain/langgraph";

const State = new StateSchema({
  results: new ReducedValue(
    z.array(z.string()).default(() => []),
    { reducer: (current, update) => current.concat(update) }
  ),
});

3. Workflows Can Become Too Rigid

// ❌ ANTI-PATTERN - Overly rigid workflow
.addEdge("validate", "process")  // Always proceeds, no error handling

// ✅ BETTER - Add conditional logic
const routeAfterValidate = (state) => {
  if (!state.validated) return "errorHandler";
  return "process";
};

.addConditionalEdges("validate", routeAfterValidate, ["process", "errorHandler"]);

4. Always Await Async Nodes

// ❌ WRONG - Forgetting await
const result = graph.invoke({ data: "test" });
console.log(result.output);  // undefined!

// ✅ CORRECT
const result = await graph.invoke({ data: "test" });
console.log(result.output);  // Works!

Links

• Workflows and Agents (JavaScript)
• Send API Guide
• Map-Reduce Example