Définir des outils pour votre Agent

Tools Give Agents Superpowers

The @tool Decorator in LangChain

from langchain_core.tools import tool

@tool
def get_weather(city: str) -> str:
    '''Get the current weather conditions for a given city.
    Use this tool when the user asks about weather in a specific location.
    Input should be just the city name, e.g. 'London' or 'New York'.
    '''
    # Real implementation would call a weather API
    return f'The weather in {city} is 18 degrees Celsius and partly cloudy.'

print(get_weather.name)         # 'get_weather'
print(get_weather.description)  # The docstring above

Type Annotations and Schema Generation

from langchain_core.tools import tool

@tool
def calculate_compound_interest(
    principal: float,
    annual_rate: float,
    years: int
) -> float:
    '''Calculate compound interest earned over a number of years.
    Args:
        principal: Initial investment amount in dollars.
        annual_rate: Annual interest rate as a decimal (e.g. 0.05 for 5%).
        years: Number of years to compound.
    Returns:
        Final amount after compounding.
    '''
    return principal * (1 + annual_rate) ** years

# Inspect the auto-generated schema
print(calculate_compound_interest.args_schema.schema())

Input Validation with Pydantic

from langchain_core.tools import tool
from pydantic import BaseModel, Field

class SearchInput(BaseModel):
    query: str = Field(description='The search query to look up.')
    num_results: int = Field(default=5, ge=1, le=20, description='Number of results to return (1-20).')

@tool(args_schema=SearchInput)
def web_search(query: str, num_results: int = 5) -> str:
    '''Search the web for current information on any topic.
    Use this for facts that may have changed after the model training cutoff.
    '''
    return f'Searching for "{query}", returning {num_results} results...'

Writing Effective Tool Descriptions

Tool Return Types

from langchain_core.tools import tool
import json

@tool
def get_stock_price(ticker: str) -> str:
    '''Look up the current stock price for a given ticker symbol.
    Input should be the stock ticker symbol in uppercase, e.g. AAPL or MSFT.
    '''
    # Stub — real implementation calls a financial API
    data = {'ticker': ticker, 'price': 182.50, 'currency': 'USD', 'change': '+1.2%'}
    return f'{ticker}: ${data["price"]} ({data["change"]})'

Handling Tool Errors Gracefully

from langchain_core.tools import tool
import requests

@tool
def fetch_url(url: str) -> str:
    '''Fetch the text content of a web page given its URL.
    Use for accessing specific documents or web pages the user references.
    '''
    try:
        resp = requests.get(url, timeout=10)
        resp.raise_for_status()
        return resp.text[:2000]  # Return first 2000 chars
    except requests.Timeout:
        return 'Error: Request timed out after 10 seconds.'
    except requests.HTTPError as e:
        return f'Error: HTTP {e.response.status_code}'
    except Exception as e:
        return f'Error fetching URL: {str(e)}'

Asynchronous Tools

from langchain_core.tools import tool
import httpx

@tool
async def async_fetch(url: str) -> str:
    '''Asynchronously fetch content from a URL.
    Preferred over fetch_url when making multiple concurrent requests.
    '''
    async with httpx.AsyncClient(timeout=10) as client:
        try:
            resp = await client.get(url)
            resp.raise_for_status()
            return resp.text[:2000]
        except Exception as e:
            return f'Error: {str(e)}'

Organizing Tools into a Toolkit

from langchain_core.tools import BaseTool
from typing import List

class WeatherToolkit:
    def __init__(self, api_key: str):
        self.api_key = api_key

    def get_tools(self) -> List[BaseTool]:
        return [
            get_weather,          # defined earlier with @tool
            get_weather_forecast,  # another tool
            get_weather_alert      # another tool
        ]

# Usage
toolkit = WeatherToolkit(api_key='your_weather_api_key')
tools = toolkit.get_tools()
print(f'Loaded {len(tools)} weather tools')

Limiting Tool Access by User Role

def get_tools_for_user(user_role: str) -> list:
    read_tools = [web_search, get_weather, calculate_compound_interest]
    write_tools = [send_email, create_calendar_event, update_record]

    if user_role == 'admin':
        return read_tools + write_tools
    elif user_role == 'member':
        return read_tools
    else:
        return [web_search]  # Guest: only public search

Tool Documentation Best Practices

Quick Check

Lesson Recap