This tutorial guides you through creating a Agent API using LangServe, enabling you to build intelligent and dynamic applications. You'll learn how to leverage LangChain agents and deploy them as production-ready APIs with ease. Discover how to define tools, orchestrate agent workflows, and expose them via a simple and scalable REST interface.
Table of Contents
References
Environment Setup
[Note]
langchain-opentutorial is a package that provides a set of easy-to-use environment setup, useful functions and utilities for tutorials.
You can alternatively set API keys in .env file and load it.
[Note] This is not necessary if you've already set API keys in previous steps.
# Set environment variables
from langchain_opentutorial import set_env
set_env(
{
"OPENAI_API_KEY": "",
"FREECURRENCY_API_KEY": ""
}
)
Environment variables have been set successfully.
LangServe
LangServe is a tool that allows you to easily deploy LangChain runnables and chains as REST APIs. It integrates with FastAPI and uses Pydantic for data validation.
Implementing a Travel Planning Agent
This section demonstrates how to implement a travel planning agent. This agent suggests customized travel plans based on the user's travel requirements.
from langchain.agents import AgentExecutor, create_openai_functions_agent
from langchain_openai import ChatOpenAI
from langchain.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain.tools import tool
from langserve import add_routes
from fastapi import FastAPI
from typing import List, Optional
from pydantic import BaseModel, Field
# Define input/output models
class TravelPlanRequest(BaseModel):
"""Travel planning request structure"""
destination: str = Field(..., description="City or country to visit")
duration: int = Field(..., description="Number of days for the trip")
interests: List[str] = Field(
default_factory=list,
description="List of interests (e.g., ['food', 'culture', 'history'])"
)
class TravelPlanResponse(BaseModel):
"""Travel planning response structure"""
itinerary: List[str]
recommendations: List[str]
estimated_budget: str
@tool
def get_travel_suggestions(destination: str, duration: int, interests: str) -> str:
"""Generates travel suggestions based on the destination, duration, and interests."""
# In a real implementation, you might use a travel API or database
return f"Here's a {duration}-day itinerary for {destination} focusing on {interests}..."
llm = ChatOpenAI(model="gpt-4.0")
prompt = ChatPromptTemplate.from_messages([
("system", "You are a helpful travel planning assistant."),
("human", "Plan a trip to {destination} for {duration} days with interests in {interests}"),
MessagesPlaceholder(variable_name="agent_scratchpad")
])
tools = [get_travel_suggestions]
agent = create_openai_functions_agent(llm, tools, prompt)
travel_executor = AgentExecutor(agent=agent, tools=tools, verbose=True)
app = FastAPI()
add_routes(
app,
travel_executor,
path="/travel-planner",
input_type=TravelPlanRequest,
output_type=TravelPlanResponse
)
Implementing a Currency exchange agent
This section shows how to implement a currency exchange agent. This agent performs currency conversions using real-time exchange rate information.
import os
import requests
from pydantic import BaseModel, Field, field_validator
from typing import Optional
from datetime import datetime
class CurrencyExchangeRequest(BaseModel):
"""Currency exchange request structure"""
amount: float = Field(..., description="Amount to convert")
from_currency: str = Field(..., description="Source currency code (e.g., USD)")
to_currency: str = Field(..., description="Target currency code (e.g., EUR)")
@field_validator('amount')
def amount_must_be_positive(cls, v):
if v <= 0:
raise ValueError('Amount must be positive')
return v
@field_validator('from_currency', 'to_currency')
def currency_must_be_valid(cls, v):
if len(v) != 3:
raise ValueError('Currency code must be 3 characters')
return v.upper()
class CurrencyExchangeResponse(BaseModel):
"""Currency exchange response structure"""
converted_amount: float
exchange_rate: float
timestamp: str
from_currency: str
to_currency: str
API_KEY = os.getenv("FREECURRENCY_API_KEY")
@tool
def get_exchange_rate(from_currency: str, to_currency: str) -> float:
"""Gets the current exchange rate between two currencies."""
url = f"https://api.freecurrencyapi.com/v1/latest"
params = {
"apikey": API_KEY,
"base_currency": from_currency,
"currencies": to_currency
}
response = requests.get(url, params=params)
data = response.json()
return data['data'][to_currency]
llm = ChatOpenAI(model="gpt-4.0")
prompt = ChatPromptTemplate.from_messages([
("system", "You are a helpful currency exchange assistant."),
("human", "Convert {amount} {from_currency} to {to_currency}"),
MessagesPlaceholder(variable_name="agent_scratchpad")
])
tools = [get_exchange_rate]
agent = create_openai_functions_agent(llm, tools, prompt)
currency_executor = AgentExecutor(agent=agent, tools=tools, verbose=True)
add_routes(
app,
currency_executor,
path="/currency-exchange",
input_type=CurrencyExchangeRequest,
output_type=CurrencyExchangeResponse
)
Testing in the LangServe Playground
LangServe provides a playground for easily testing the implemented agents. This allows you to directly verify and debug the API's behavior.
INFO: Started server process [25888]
INFO: Waiting for application startup.
INFO: Application startup complete.
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
