langgraph-patterns

LangGraph Patterns

Canonical, copy-paste recipes for LangGraph >= 1.0 (verified against 1.0.x and 1.1.x). Every snippet here is a minimal working pattern you can extend; do not paste them into production verbatim without adapting names and types to the project.

The snippets use a recurring example graph (a research assistant with clarity → research → validator → synthesis nodes) purely to make the patterns concrete. Swap in your own domain. myapp is a placeholder for your package name.

When To Use

• Designing a new graph (consult sections 1-7 first).
• Implementing a node, router, or interrupt (sections 4-8, 11).
• Wiring tools, MCP servers, or providers (sections 12-13).
• Adding subgraphs, fan-out parallelism, async streaming, or tracing (sections 14-17).
• Debugging a graph that "feels off" (section 18: common mistakes catalog with fixes).
• Writing tests against a graph (section 19).

0. Install and Imports

Pin minimum versions in pyproject.toml:

[project]
dependencies = [
  "langgraph>=1.0,<2",
  "langchain-core>=0.3",
  "langchain-openai>=0.2",
  "pydantic>=2.7",
]

[project.optional-dependencies]
sqlite = ["langgraph-checkpoint-sqlite>=2.0"]  # only if you persist via SqliteSaver

Imports cheat-sheet (all from the public API):

from typing import Annotated, Literal, TypedDict, Any
from pydantic import BaseModel, Field
from langchain_core.messages import AnyMessage, HumanMessage, AIMessage
from langchain_openai import ChatOpenAI
from langgraph.graph import StateGraph, START, END
from langgraph.graph.message import add_messages
from langgraph.types import Command, interrupt
from langgraph.checkpoint.memory import MemorySaver
from langgraph.checkpoint.sqlite import SqliteSaver  # optional

If an import path is not in the list above, double-check it; internal modules move between minor versions.

1. Typed State with add_messages Reducer

The standard State shape. The Annotated[..., add_messages] reducer is what enables append-style conversation history; without it, every node's return value overwrites prior messages.