langchain

LangChain Skill

Build production AI agents using LangChain's pre-built architecture and integrations.

Installation

pip install langchain langchain-anthropic langgraph
# For MCP support
pip install langchain-mcp-adapters

Quick Agent

from langchain.agents import create_agent
from langchain.tools import tool

@tool
def get_weather(city: str) -> str:
    """Get weather for a city."""
    return f"Sunny in {city}!"

agent = create_agent(
    model="claude-sonnet-4-5-20250929",
    tools=[get_weather],
    system_prompt="You are a helpful assistant"
)

result = agent.invoke({"messages": [{"role": "user", "content": "Weather in SF?"}]})

Tools

Define tools with @tool decorator. Type hints required, docstring becomes description:

from langchain.tools import tool, ToolRuntime
from dataclasses import dataclass

@tool
def search(query: str, limit: int = 10) -> str:
    """Search database for records."""
    return f"Found {limit} results for '{query}'"

# With runtime context access
@dataclass
class Context:
    user_id: str

@tool
def get_user_data(runtime: ToolRuntime[Context]) -> str:
    """Get current user data."""
    user_id = runtime.context.user_id
    return f"Data for {user_id}"

ToolRuntime Access

• runtime.state - Agent state (messages, custom fields)
• runtime.context - Immutable config (user_id, session)
• runtime.store - Persistent memory across conversations
• runtime.stream_writer - Stream updates during execution

Reserved Parameters

Cannot use as tool args: config, runtime

Memory

from langgraph.checkpoint.memory import InMemorySaver
from langgraph.store.memory import InMemoryStore

# Short-term (conversation) memory
checkpointer = InMemorySaver()

# Long-term (cross-conversation) memory
store = InMemoryStore()

agent = create_agent(
    model="claude-sonnet-4-5-20250929",
    tools=[...],
    checkpointer=checkpointer,
    store=store
)

# Use thread_id for conversation continuity
config = {"configurable": {"thread_id": "conversation-1"}}
agent.invoke({"messages": [...]}, config=config)