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Choosing between multiple tools

In our Quickstart we went over how to build a Chain that calls a single multiply tool. Now let's take a look at how we might augment this chain so that it can pick from a number of tools to call. We'll focus on Chains since Agents can route between multiple tools by default.


We'll need to install the following packages for this guide:

%pip install --upgrade --quiet langchain-core

If you'd like to trace your runs in LangSmith uncomment and set the following environment variables:

import getpass
import os

# os.environ["LANGCHAIN_TRACING_V2"] = "true"
# os.environ["LANGCHAIN_API_KEY"] = getpass.getpass()


Recall we already had a multiply tool:

from import tool

def multiply(first_int: int, second_int: int) -> int:
"""Multiply two integers together."""
return first_int * second_int

API Reference:

And now we can add to it an exponentiate and add tool:

def add(first_int: int, second_int: int) -> int:
"Add two integers."
return first_int + second_int

def exponentiate(base: int, exponent: int) -> int:
"Exponentiate the base to the exponent power."
return base**exponent

The main difference between using one Tool and many is that we can't be sure which Tool the model will invoke upfront, so we cannot hardcode, like we did in the Quickstart, a specific tool into our chain. Instead we'll add call_tools, a RunnableLambda that takes the output AI message with tools calls and routes to the correct tools.

Install dependencies
pip install -qU langchain-openai
Set environment variables
import getpass
import os

os.environ["OPENAI_API_KEY"] = getpass.getpass()
from langchain_openai import ChatOpenAI

llm = ChatOpenAI(model="gpt-3.5-turbo-0125")
from operator import itemgetter
from typing import Dict, List, Union

from langchain_core.messages import AIMessage
from langchain_core.runnables import (

tools = [multiply, exponentiate, add]
llm_with_tools = llm.bind_tools(tools)
tool_map = { tool for tool in tools}

def call_tools(msg: AIMessage) -> Runnable:
"""Simple sequential tool calling helper."""
tool_map = { tool for tool in tools}
tool_calls = msg.tool_calls.copy()
for tool_call in tool_calls:
tool_call["output"] = tool_map[tool_call["name"]].invoke(tool_call["args"])
return tool_calls

chain = llm_with_tools | call_tools
chain.invoke("What's 23 times 7")
[{'name': 'multiply',
'args': {'first_int': 23, 'second_int': 7},
'id': 'toolu_01Wf8kUs36kxRKLDL8vs7G8q',
'output': 161}]
chain.invoke("add a million plus a billion")
[{'name': 'add',
'args': {'first_int': 1000000, 'second_int': 1000000000},
'id': 'toolu_012aK4xZBQg2sXARsFZnqxHh',
'output': 1001000000}]
chain.invoke("cube thirty-seven")
[{'name': 'exponentiate',
'args': {'base': 37, 'exponent': 3},
'id': 'toolu_01VDU6X3ugDb9cpnnmCZFPbC',
'output': 50653}]

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