You can try to force JSON output using function calling (you have to use either the gpt-3.5-turbo-0613 or gpt-4-0613 model for now).

Think of the properties you want in the JSON object, then send those to ChatGPT as required parameters for a function (even if that function doesn't exist).

    # Definition of our local function(s).
    # This is effectively telling ChatGPT what we're going to use its JSON output for.
    # Send this alongside the "model" and "messages" properties in the API request.

    functions = [
        {
            "name": "write_post",
            "description": "Shows the title and summary of some text.",
            "parameters": {
                "type": "object",
                "properties": {
                    "title": {
                        "type": "string",
                        "description": "Title of the text output."
                    },
                    "summary": {
                        "type": "string",
                        "description": "Summary of the text output."
                    }
                }
            }
        }
    ]

I've found it's not perfect but still pretty reliable – good enough for me combined with error handling.

If you're interested, I wrote a blog post with more detail: https://puppycoding.com/2023/07/07/json-object-from-chatgpt-...