LangGraph Tutor Skill

Expert guidance for building production AI agents with LangGraph.

Quick Start

from langgraph.graph import StateGraph, START, END
from typing import Annotated
from typing_extensions import TypedDict
from langgraph.graph.message import add_messages

class State(TypedDict):
    messages: Annotated[list, add_messages]

def chatbot(state: State):
    return {"messages": [llm.invoke(state["messages"])]}

graph = StateGraph(State)
graph.add_node("chatbot", chatbot)
graph.add_edge(START, "chatbot")
graph.add_edge("chatbot", END)
app = graph.compile()

Core Concepts

1. State Definition

State flows through the graph. Use TypedDict with optional reducers:

class State(TypedDict):
    messages: Annotated[list, add_messages]  # Accumulates
    context: str                              # Overwrites
    count: Annotated[int, operator.add]       # Sums

2. Nodes

Functions that receive state and return updates:

def my_node(state: State) -> dict:
    # Read from state
    messages = state["messages"]
    # Return updates (don't mutate!)
    return {"context": "new value"}

3. Edges

Connect nodes in the graph:

graph.add_edge(START, "node_a")      # Entry point
graph.add_edge("node_a", "node_b")   # Linear flow
graph.add_edge("node_b", END)        # Exit point

4. Conditional Routing

Route based on state:

def router(state: State) -> Literal["path_a", "path_b"]:
    if condition:
        return "path_a"
    return "path_b"

graph.add_conditional_edges("source", router)

5. Memory/Checkpointing

Persist state across invocations:

from langgraph.checkpoint.memory import InMemorySaver

memory = InMemorySaver()
app = graph.compile(checkpointer=memory)

config = {"configurable": {"thread_id": "user-123"}}
result = app.invoke({"messages": [msg]}, config)

6. Human-in-the-Loop

Pause for human input:

from langgraph.types import interrupt

def approval_node(state):
    response = interrupt({"question": "Approve?"})
    return {"approved": response["answer"]}

Common Patterns

ReAct Agent (Reasoning + Acting)

See references/patterns.md for full implementation.

Supervisor Multi-Agent

See references/multi-agent.md for patterns.

Tool Calling

See references/tools.md for integration.

Validation

Run the validation script to check your graph:

python scripts/validate_graph.py your_graph.py

Examples

Working examples in examples/:

• simple_chatbot.py – Minimal chatbot
• tool_agent.py – Agent with tools
• multi_agent.py – Supervisor pattern

Common Errors

Resources

• LangGraph Docs
• Tutorials
• API Reference