LangGraph Tutorial Build Multi Agent System 2026

LangGraph uses graphs to manage agent state and workflows. This guide walks you through building a multi-agent collaboration system from scratch.

💡 What You Will Learn

LangGraph uses graphs to manage agent state and workflows. This guide walks you through building a multi-agent collaboration system from scratch.

📜 Table of Contents

• Core Concepts
• Summary

Core Concepts

from langgraph.graph import StateGraph, END
from typing import TypedDict, List

class AgentState(TypedDict):
    messages: List[str]
    next_agent: str

# DefineAgent
def researcher(state: AgentState):
    # Agent
    return {"messages": ["Research complete"]}

def writer(state: AgentState):
    # Agent
    return {"messages": ["Writing complete"]}

def reviewer(state: AgentState):
    # Agent
    return {"messages": ["Review complete"]}

# Graph
graph = StateGraph(AgentState)
graph.add_node("researcher", researcher)
graph.add_node("writer", writer)
graph.add_node("reviewer", reviewer)

graph.set_entry_point("researcher")
graph.add_edge("researcher", "writer")
graph.add_edge("writer", "reviewer")
graph.add_conditional_edges(
    "reviewer",
    lambda s: "writer" if "need_revision" in s else END
)

Summary