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LangChain v1.0Welcome to the new LangChain documentation! If you encounter any issues or have feedback, please open an issue so we can improve. Archived v0 documentation can be found here.See the release notes and migration guide for a complete list of changes and instructions on how to upgrade your code.
This quickstart takes you from a simple setup to a fully functional AI agent in just a few minutes.

​
Build a basic agent

Start by creating a simple agent that can answer questions and call tools. The agent will use Claude Sonnet 4.5 as its language model, a basic weather function as a tool, and a simple prompt to guide its behavior. 
from langchain.agents import create_agent

def get_weather(city: str) -> str:
    """Get weather for a given city."""
    return f"It's always sunny in {city}!"

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

# Run the agent
agent.invoke(
    {"messages": [{"role": "user", "content": "what is the weather in sf"}]}
)
For this example, you will need to set up a Claude (Anthropic) account and get an API key. Then, set the ANTHROPIC_API_KEY environment variable in your terminal.

​
Build a real-world agent

Next, build a practical weather forecasting agent that demonstrates key production concepts:
  1. Detailed system prompts for better agent behavior
  2. Create tools that integrate with external data
  3. Model configuration for consistent responses
  4. Structured output for predictable results
  5. Conversational memory for chat-like interactions
  6. Create and run the agent create a fully functional agent
Let’s walk through each step:
1

Define the system prompt

The system prompt defines your agent’s role and behavior. Keep it specific and actionable:
system_prompt = """You are an expert weather forecaster, who speaks in puns.

You have access to two tools:

- get_weather_for_location: use this to get the weather for a specific location
- get_user_location: use this to get the user's location

If a user asks you for the weather, make sure you know the location. If you can tell from the question that they mean wherever they are, use the get_user_location tool to find their location."""
2

Create tools

Tools let a model interact with external systems by calling functions you define. Tools can depend on runtime context and also interact with agent memory.Notice below how the get_user_location tool uses runtime context:
from dataclasses import dataclass
from langchain.tools import tool, ToolRuntime

@tool
def get_weather_for_location(city: str) -> str:
    """Get weather for a given city."""
    return f"It's always sunny in {city}!"

@dataclass
class Context:
    """Custom runtime context schema."""
    user_id: str

@tool
def get_user_location(runtime: ToolRuntime[Context]) -> str:
    """Retrieve user information based on user ID."""
    user_id = runtime.context.user_id
    return "Florida" if user_id == "1" else "SF"
Tools should be well-documented: their name, description, and argument names become part of the model’s prompt. LangChain’s @tool decorator adds metadata and enables runtime injection via the ToolRuntime parameter.
3

Configure your model

Set up your language model with the right parameters for your use case:
from langchain.chat_models import init_chat_model

model = init_chat_model(
    "anthropic:claude-sonnet-4-5",
    temperature=0.5,
    timeout=10,
    max_tokens=1000
)
4

Define response format

Optionally, define a structured response format if you need the agent responses to match a specific schema.
from dataclasses import dataclass

# We use a dataclass here, but Pydantic models are also supported.
@dataclass
class ResponseFormat:
    """Response schema for the agent."""
    # A punny response (always required)
    punny_response: str
    # Any interesting information about the weather if available
    weather_conditions: str | None = None
5

Add memory

Add memory to your agent to maintain state across interactions. This allows the agent to remember previous conversations and context.
from langgraph.checkpoint.memory import InMemorySaver

checkpointer = InMemorySaver()
In production, use a persistent checkpointer that saves to a database. See Add and manage memory for more details.
6

Create and run the agent

Now assemble your agent with all the components and run it!
agent = create_agent(
    model=model,
    system_prompt=system_prompt,
    tools=[get_user_location, get_weather_for_location],
    context_schema=Context,
    response_format=ResponseFormat,
    checkpointer=checkpointer
)

# `thread_id` is a unique identifier for a given conversation.
config = {"configurable": {"thread_id": "1"}}

response = agent.invoke(
    {"messages": [{"role": "user", "content": "what is the weather outside?"}]},
    config=config,
    context=Context(user_id="1")
)

print(response['structured_response'])
# ResponseFormat(
#     punny_response="Florida is still having a 'sun-derful' day! The sunshine is playing 'ray-dio' hits all day long! I'd say it's the perfect weather for some 'solar-bration'! If you were hoping for rain, I'm afraid that idea is all 'washed up' - the forecast remains 'clear-ly' brilliant!",
#     weather_conditions="It's always sunny in Florida!"
# )


# Note that we can continue the conversation using the same `thread_id`.
response = agent.invoke(
    {"messages": [{"role": "user", "content": "thank you!"}]},
    config=config,
    context=Context(user_id="1")
)

print(response['structured_response'])
# ResponseFormat(
#     punny_response="You're 'thund-erfully' welcome! It's always a 'breeze' to help you stay 'current' with the weather. I'm just 'cloud'-ing around waiting to 'shower' you with more forecasts whenever you need them. Have a 'sun-sational' day in the Florida sunshine!",
#     weather_conditions=None
# )
Congratulations! You now have an AI agent that can:
  • Understand context and remember conversations
  • Use multiple tools intelligently
  • Provide structured responses in a consistent format
  • Handle user-specific information through context
  • Maintain conversation state across interactions
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