langchain/docs/docs/how_to/tool_calling_parallel.ipynb

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    "# How to disable parallel tool calling\n",
    "\n",
    ":::info Provider-specific\n",
    "\n",
    "This API is currently only supported by OpenAI and Anthropic.\n",
    "\n",
    ":::\n",
    "\n",
    "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."
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "First let's set up our tools and model:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "from langchain_core.tools import tool\n",
    "\n",
    "\n",
    "@tool\n",
    "def add(a: int, b: int) -> int:\n",
    "    \"\"\"Adds a and b.\"\"\"\n",
    "    return a + b\n",
    "\n",
    "\n",
    "@tool\n",
    "def multiply(a: int, b: int) -> int:\n",
    "    \"\"\"Multiplies a and b.\"\"\"\n",
    "    return a * b\n",
    "\n",
    "\n",
    "tools = [add, multiply]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import os\n",
    "from getpass import getpass\n",
    "\n",
    "from langchain.chat_models import init_chat_model\n",
    "\n",
    "if \"OPENAI_API_KEY\" not in os.environ:\n",
    "    os.environ[\"OPENAI_API_KEY\"] = getpass()\n",
    "\n",
    "llm = init_chat_model(\"openai:gpt-4.1-mini\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now let's show a quick example of how disabling parallel tool calls work:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[{'name': 'add',\n",
       "  'args': {'a': 2, 'b': 2},\n",
       "  'id': 'call_Hh4JOTCDM85Sm9Pr84VKrWu5'}]"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "llm_with_tools = llm.bind_tools(tools, parallel_tool_calls=False)\n",
    "llm_with_tools.invoke(\"Please call the first tool two times\").tool_calls"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "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."
   ]
  },
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   "source": []
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