JSON mode vs structured outputs: the difference

import os
from openai import OpenAI
import json

client = OpenAI(api_key=os.environ.get('OPENAI_API_KEY'))

user_text = "I bought 3 apples at $2.50 each and 2 oranges at $1.75 each"

print("=== JSON MODE ===")
response_json_mode = client.chat.completions.create(
    model="gpt-4.1",
    messages=[
        {
            "role": "user",
            "content": f"Extract the items and prices from this receipt: {user_text}. Return valid JSON only."
        }
    ],
    response_format={"type": "json_object"}
)
print(response_json_mode.choices[0].message.content)
print()

print("=== STRUCTURED OUTPUTS ===")
response_structured = client.chat.completions.create(
    model="gpt-4.1",
    messages=[
        {
            "role": "user",
            "content": f"Extract the items and prices from this receipt: {user_text}"
        }
    ],
    response_format={
        "type": "json_schema",
        "json_schema": {
            "name": "receipt_items",
            "schema": {
                "type": "object",
                "properties": {
                    "items": {
                        "type": "array",
                        "items": {
                            "type": "object",
                            "properties": {
                                "name": {"type": "string"},
                                "quantity": {"type": "integer"},
                                "unit_price": {"type": "number"},
                                "total": {"type": "number"}
                            },
                            "required": ["name", "quantity", "unit_price", "total"]
                        }
                    },
                    "grand_total": {"type": "number"}
                },
                "required": ["items", "grand_total"]
            },
            "strict": True
        }
    }
)
data = json.loads(response_structured.choices[0].message.content)
print(json.dumps(data, indent=2))
print()
print(f"Grand total parsed as number: {data['grand_total']}")
print(f"First item: {data['items'][0]['name']} x {data['items'][0]['quantity']}")