feat(langchain_v1): add llm selection middleware (#33272)
* Add llm based tool selection middleware.
* Note that we might want some form of caching for when the agent is
inside an active tool calling loop as the tool selection isn't expected
to change during that time.
API:
```python
class LLMToolSelectorMiddleware(AgentMiddleware):
"""Uses an LLM to select relevant tools before calling the main model.
When an agent has many tools available, this middleware filters them down
to only the most relevant ones for the user's query. This reduces token usage
and helps the main model focus on the right tools.
Examples:
Limit to 3 tools:
```python
from langchain.agents.middleware import LLMToolSelectorMiddleware
middleware = LLMToolSelectorMiddleware(max_tools=3)
agent = create_agent(
model="openai:gpt-4o",
tools=[tool1, tool2, tool3, tool4, tool5],
middleware=[middleware],
)
```
Use a smaller model for selection:
```python
middleware = LLMToolSelectorMiddleware(model="openai:gpt-4o-mini", max_tools=2)
```
"""
def __init__(
self,
*,
model: str | BaseChatModel | None = None,
system_prompt: str = DEFAULT_SYSTEM_PROMPT,
max_tools: int | None = None,
always_include: list[str] | None = None,
) -> None:
"""Initialize the tool selector.
Args:
model: Model to use for selection. If not provided, uses the agent's main model.
Can be a model identifier string or BaseChatModel instance.
system_prompt: Instructions for the selection model.
max_tools: Maximum number of tools to select. If the model selects more,
only the first max_tools will be used. No limit if not specified.
always_include: Tool names to always include regardless of selection.
These do not count against the max_tools limit.
"""
```
```python
"""Test script for LLM tool selection middleware."""
from langchain.agents import create_agent
from langchain.agents.middleware import LLMToolSelectorMiddleware
from langchain_core.tools import tool
@tool
def get_weather(location: str) -> str:
"""Get current weather for a location."""
return f"Weather in {location}: 72°F, sunny"
@tool
def search_web(query: str) -> str:
"""Search the web for information."""
return f"Search results for: {query}"
@tool
def calculate(expression: str) -> str:
"""Perform mathematical calculations."""
return f"Result of {expression}: 42"
@tool
def send_email(to: str, subject: str) -> str:
"""Send an email to someone."""
return f"Email sent to {to} with subject: {subject}"
@tool
def get_stock_price(symbol: str) -> str:
"""Get current stock price for a symbol."""
return f"Stock price for {symbol}: $150.25"
@tool
def translate_text(text: str, target_language: str) -> str:
"""Translate text to another language."""
return f"Translated '{text}' to {target_language}"
@tool
def set_reminder(task: str, time: str) -> str:
"""Set a reminder for a task."""
return f"Reminder set: {task} at {time}"
@tool
def get_news(topic: str) -> str:
"""Get latest news about a topic."""
return f"Latest news about {topic}"
@tool
def book_flight(destination: str, date: str) -> str:
"""Book a flight to a destination."""
return f"Flight booked to {destination} on {date}"
@tool
def get_restaurant_recommendations(city: str, cuisine: str) -> str:
"""Get restaurant recommendations."""
return f"Top {cuisine} restaurants in {city}"
# Create agent with tool selection middleware
middleware = LLMToolSelectorMiddleware(
model="openai:gpt-4o-mini",
max_tools=3,
)
agent = create_agent(
model="openai:gpt-4o",
tools=[
get_weather,
search_web,
calculate,
send_email,
get_stock_price,
translate_text,
set_reminder,
get_news,
book_flight,
get_restaurant_recommendations,
],
middleware=[middleware],
)
# Test with a query that should select specific tools
response = agent.invoke(
{"messages": [{"role": "user", "content": "I need to find restaurants"}]}
)
print(response)
```
