LangGraph Tutor Skill
Expert guidance for building production AI agents with LangGraph.
Quick Start
python
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:
python
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:
python
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:
python
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:
python
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:
python
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:
python
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:
bash
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
| Error | Cause | Fix |
|---|---|---|
| "Node has no outgoing edge" | Missing edge | Add edge to END or next node |
| "State key not found" | Accessing undefined key | Check State TypedDict |
| "Cannot serialize" | Complex objects in state | Use JSON-serializable types |