Langgraph

LangGraph Skill

Overview

LangGraph is a library for building stateful, multi-actor AI applications with LLMs. It extends LangChain to support cyclic graphs, enabling sophisticated agent workflows with fine-grained control over state, flow, and memory.

Key Concepts

Graph Types

• StateGraph: Primary graph type with shared state schema across nodes
• MessageGraph: Simplified graph where state is a list of messages

Core Components

• Nodes: Python functions or runnables that read/write state
• Edges: Connections between nodes (conditional or fixed)
• State: Typed dict schema shared across all nodes
• Checkpointers: Persist state between runs (memory, SQLite, Postgres)

Basic Usage

from langgraph.graph import StateGraph, END
from typing import TypedDict, Annotated
import operator

class AgentState(TypedDict):
    messages: Annotated[list, operator.add]
    next: str

def agent_node(state: AgentState):
    return {"messages": [response], "next": "tool" if needs_tool else END}

def tool_node(state: AgentState):
    return {"messages": [tool_result]}

graph = StateGraph(AgentState)
graph.add_node("agent", agent_node)
graph.add_node("tools", tool_node)
graph.set_entry_point("agent")
graph.add_conditional_edges("agent", lambda s: s["next"], {"tool": "tools", END: END})
graph.add_edge("tools", "agent")

app = graph.compile()
result = app.invoke({"messages": [HumanMessage(content="Hello")], "next": ""})

ReAct Agent (Prebuilt)

from langgraph.prebuilt import create_react_agent
from langchain_openai import ChatOpenAI

llm = ChatOpenAI(model="gpt-4o")
agent = create_react_agent(llm, tools=[search_tool, calculator_tool])
result = agent.invoke({"messages": [("user", "What is 2+2?")]})

Persistence / Memory

from langgraph.checkpoint.memory import MemorySaver
from langgraph.checkpoint.sqlite import SqliteSaver

checkpointer = SqliteSaver.from_conn_string("checkpoints.db")
app = graph.compile(checkpointer=checkpointer)

config = {"configurable": {"thread_id": "user-123"}}
result = app.invoke(input, config=config)

Human-in-the-Loop

from langgraph.graph import interrupt

def approval_node(state):
    decision = interrupt("Approve this action? (yes/no)")
    return {"approved": decision == "yes"}

app = graph.compile(checkpointer=checkpointer, interrupt_before=["approval"])
app.invoke(Command(resume="yes"), config=config)

Streaming

for chunk in app.stream(input, stream_mode="values"):
    print(chunk)

async for chunk in app.astream(input):
    print(chunk)

Installation

pip install langgraph
pip install langgraph-checkpoint-sqlite
pip install langgraph-checkpoint-postgres

Key Tips

• Use Annotated[list, operator.add] for accumulating state fields
• Always compile with checkpointer for stateful/conversational apps
• Use interrupt_before/interrupt_after for human-in-the-loop workflows
• Sub-graphs can be compiled and used as nodes in parent graphs
• Fan-out to parallel nodes: graph.add_edge("start", ["node_a", "node_b"])

Related Skills

• langchain — LangChain foundation
• multi-agent-orchestration — multi-agent patterns
• crewai — alternative agent framework

GitNexus Index

This skill is indexed by GitNexus for knowledge graph traversal. Index path: /Users/localuser/.claude/skills/langgraph/.gitnexus Last indexed: 2026-05-23