Building AI Agents with LangChain and LangGraph: Part 1 › Putting It All Together

Michael BrenndoerferJuly 21, 20251 min read
Building AI Agents with LangChain and LangGraph: Part 1 › Putting It All TogetherOne section · Sections in this article7 / 8 ↓
Sections in this article8
Reading tools Definitions & inline links

Toggle tooltip visibility. Hover over underlined terms for instant definitions.

Article links

Make inline references clickable

Let's create a minimal CLI tool that demonstrates everything we've learned. Save this as reply_agent.py and run it from your terminal:

from langchain.chat_models import init_chat_model
from langchain.tools import tool

@tool
def draft_customer_reply(customer_name: str, request_category: str, reply: str) -> str:
    """Draft a reply to a customer."""
    return f"I am drafting a reply to {customer_name} in the category {request_category}.\n Content: {reply}"


def main():
    # Initialize model
    llm = init_chat_model(
        "google_vertexai:gemini-2.0-flash",
        temperature=0
    )

    agent = llm.bind_tools(
        [draft_customer_reply],
        tool_choice="any", # force using a tool
        parallel_tool_calls=False
    )

    # Get user input
    request = input("What message would you like to send? ")

    # Get tool call from model
    response = agent.invoke(request)

    if response.tool_calls:
        # Execute the tool
        args = response.tool_calls[0]["args"]
        result = draft_customer_reply.invoke(args)
        print(f"Result: {result}")
    else:
        print("No reply needed.")

if __name__ == "__main__":
    main()

Usage: python reply_agent.py then type 'Let John know that his request for a refund has been processed.'

In[74]:
Code
print("What message would you like to send?")
print("tell frank pacakge is on the way")
print("Result: I am drafting a reply to Marco in the category Package Delivery.")
print("Content: Frank, your package is on the way!")
Out[74]:
Console
What message would you like to send?
tell frank pacakge is on the way
Result: I am drafting a reply to Marco in the category Package Delivery.
Content: Frank, your package is on the way!