Structured JSON output for automation

You need: a fetch_... key (create one), a balance of at least $0.01 (top up), Python 3.10+ with pip install openai pydantic or Node.js 18+ with npm install openai zod.

1. 1
   Describe the fields

   Types: string, number, yes/no, a choice from a list. For a list, always set enum, or you'll get "Delivery", "delivery" and "shipping".

2. 2
   Send a request with the schema

   response_format with json_schema and strict: true — example 1. Few fields? json_object with the fields in the prompt is enough — example 2.

3. 3
   Validate the answer in code

   pydantic or zod. Even a strict schema doesn't guarantee a correct answer.

4. 4
   Give a second chance

   If validation fails, show the model its answer and the error and ask for corrected JSON. Fails again — hand the document to a person.

1Modes and models

Test other models on 20–50 of your own examples. Prices: Models and pricing.

2Example 1. Invoice data, strict schema

"""
Invoice data as JSON that follows a strict schema.
pip install openai pydantic
"""
import os
from typing import Literal

from openai import OpenAI
from pydantic import BaseModel, ConfigDict, Field, ValidationError

MODEL = "deepseek-v4.1-flash"  # or "claude-haiku-5-5"

client = OpenAI(
    base_url="https://api.zukko.pro/v1",

In Node.js the schema for the model and the zod schema are written separately — keep them in sync. In Python both come from the Invoice class.

3Example 2. Support ticket triage, json_object mode

"""
Triage a support ticket: category, priority, whether a human is needed.
pip install openai pydantic
"""
import os
from typing import Literal

from openai import OpenAI
from pydantic import BaseModel, ValidationError

client = OpenAI(
    base_url="https://api.zukko.pro/v1",
    api_key=os.environ["ZUKKO_API_KEY"],
    timeout=60,

4Schema rules

• Numbers as numbers (1540.05, not "EUR 1,540.05"), currency in its own field.
• Dates as strings, format in the field description: YYYY-MM-DD.
• 5–10 fields, no deep nesting.
• Every field in required, additionalProperties: false. pydantic with extra="forbid" does this for you.

5If it doesn't work