How to disable parallel tool calling

Provider-specific

This API is currently only supported by OpenAI and Anthropic.

OpenAI tool calling performs tool calling in parallel by default. That means that if we ask a question like "What is the weather in Tokyo, New York, and Chicago?" and we have a tool for getting the weather, it will call the tool 3 times in parallel. We can force it to call only a single tool once by using the parallel_tool_call parameter.

First let's set up our tools and model:

from langchain_core.tools import tool


@tool
def add(a: int, b: int) -> int:
    """Adds a and b."""
    return a + b


@tool
def multiply(a: int, b: int) -> int:
    """Multiplies a and b."""
    return a * b


tools = [add, multiply]

API Reference:tool

import os
from getpass import getpass

from langchain.chat_models import init_chat_model

if "OPENAI_API_KEY" not in os.environ:
    os.environ["OPENAI_API_KEY"] = getpass()

llm = init_chat_model("openai:gpt-4.1-mini")

API Reference:init_chat_model

Now let's show a quick example of how disabling parallel tool calls work:

llm_with_tools = llm.bind_tools(tools, parallel_tool_calls=False)
llm_with_tools.invoke("Please call the first tool two times").tool_calls

[{'name': 'add',
  'args': {'a': 2, 'b': 2},
  'id': 'call_Hh4JOTCDM85Sm9Pr84VKrWu5'}]

As we can see, even though we explicitly told the model to call a tool twice, by disabling parallel tool calls the model was constrained to only calling one.