Incomplete tool schema being sent to OpenAI models causing incorrect tool calls and failures with array arguments

[padambengani]

ChatOCIGenAI is sending incomplete tool schema to openai models causing following issues:

1. throws "array schema missing items" error when the tool have any array argument
2. Tool calls are made with incorrect parameters due to missing info in tool schema sent by ChatOCIGenAI to openai models

Following is the example to reproduce the error:

from langchain_oci import ChatOCIGenAI
from langchain_core.tools import tool
from typing import Any, Dict, List, Literal, Optional
import json

llm = ChatOCIGenAI(
    service_endpoint=SERVICE_ENDPOINT,
    auth_file_location=AUTH_FILE_LOCATION,
    auth_profile=AUTH_PROFILE,
    compartment_id=COMPARTMENT_OCID,
    model_id="openai.gpt-5",
)

@tool
def get_weather_m(cities: list[str], unit: Literal["C", "F"] = None) -> str:
        """
        Get the weather of list of cities.

        Args:
            cities (list[str]): List of cities (maximum 2 cities)
        """

        return f"It is Sunny in all these {cities}"


@tool
def get_weather(city: str) -> str:
        """
        Get the weather of a city.
        """

        return f"It is Sunny in {city}"


print("Actual tool schema:")
print(json.dumps(get_weather_m.tool_call_schema.model_json_schema(), indent=4))

llm_with_tools = llm.bind_tools([get_weather_m])
print(llm_with_tools.invoke("How's the weather in these cities: New York City, London?"))

Output:

Actual tool schema:
{
    "description": "Get the weather of list of cities.\n\nArgs:\n    cities (list[str]): List of cities (maximum 2 cities)",
    "properties": {
        "cities": {
            "items": {
                "type": "string"
            },
            "title": "Cities",
            "type": "array"
        },
        "unit": {
            "default": null,
            "enum": [
                "C",
                "F"
            ],
            "title": "Unit",
            "type": "string"
        }
    },
    "required": [
        "cities"
    ],
    "title": "get_weather_m",
    "type": "object"
}

Tool Schema sent by ChatOCIGenAI:
{
  "description": "Get the weather of list of cities.",
  "name": "get_weather_m",
  "parameters": {
    "properties": {
      "cities": {
        "description": "",
        "type": "array"
      },
      "unit": {
        "description": "",
        "type": "string"
      }
    },
    "required": [
      "cities"
    ],
    "type": "object"
  },
  "type": "FUNCTION"
}


oci.exceptions.ServiceError: {'target_service': 'generative_ai_inference', 'status': 400, 'code': '400', 'opc-request-id': '3186543F6EF5470CBFFCA6B1DE622E3D/D45C4FA8C4A6A0C02A8F445F5978CDD9/38F12E2298B43A23010291ED0FFA8379', 'message': '{\n  "error": {\n    "message": "Invalid schema for function \'get_weather_m\': In context=(\'properties\', \'cities\'), array schema missing items.",\n    "type": "invalid_request_error",\n    "param": "tools[0].function.parameters",\n    "code": "invalid_function_parameters"\n  }\n}', 'operation_name': 'chat', 'timestamp': '2025-09-30T05:14:58.883334+00:00', 'client_version': 'Oracle-PythonSDK/2.145.0', 'request_endpoint': 'POST https://inference.generativeai.us-chicago-1.oci.oraclecloud.com/20231130/actions/chat', 'logging_tips': 'To get more info on the failing request, refer to https://docs.oracle.com/en-us/iaas/tools/python/latest/logging.html for ways to log the request/response details.', 'troubleshooting_tips': "See https://docs.oracle.com/iaas/Content/API/References/apierrors.htm#apierrors_400__400_400 for more information about resolving this error. Also see https://docs.oracle.com/iaas/api/#/en/generative-ai-inference/20231130/ChatResult/Chat for details on this operation's requirements. If you are unable to resolve this generative_ai_inference issue, please contact Oracle support and provide them this full error message."}