Structured JSON output

Ask for JSON with response_format. With a schema and strict: true, ZenithAI checks the answer against your schema before returning it.

Python

from openai import OpenAI
from pydantic import BaseModel

class Invoice(BaseModel):
    vendor: str
    invoice_number: str
    invoice_date: str      # DD-MM-YYYY
    total_inr: float

client = OpenAI(base_url="https://dummydomain/v1", api_key="YOUR_API_KEY")

reply = client.chat.completions.create(
    model="Fast",
    messages=[{"role": "user", "content": "Extract the invoice fields:\n" + invoice_text}],
    response_format={
        "type": "json_schema",
        "json_schema": {"name": "Invoice", "schema": Invoice.model_json_schema(), "strict": True},
    },
)
invoice = Invoice.model_validate_json(reply.choices[0].message.content)

JavaScript

import OpenAI from "openai";
import { z } from "zod";
import { zodToJsonSchema } from "zod-to-json-schema";

const Invoice = z.object({
  vendor: z.string(), invoice_number: z.string(), invoice_date: z.string(), total_inr: z.number(),
});

const client = new OpenAI({ baseURL: "https://dummydomain/v1", apiKey: process.env.API_KEY });
const reply = await client.chat.completions.create({
  model: "Fast",
  messages: [{ role: "user", content: `Extract the invoice fields:\n${invoiceText}` }],
  response_format: { type: "json_schema",
    json_schema: { name: "Invoice", strict: true, schema: zodToJsonSchema(Invoice, { target: "openAi" }) } },
});
const invoice = Invoice.parse(JSON.parse(reply.choices[0].message.content));

Two modes

• {"type": "json_object"} returns one valid JSON object, with no schema.
• {"type": "json_schema", "json_schema": {"name": ..., "schema": ..., "strict": true}} follows your schema. name may use letters, digits, _ and -, up to 64 characters.

Schemas use JSON Schema 2020-12. Local $defs/$ref, anyOf/oneOf and nullable fields work, so Pydantic v2 and Zod schemas can be used as they are. Remote or recursive references are refused.

What is checked

The structure (types, properties, required fields, enums) is followed while the answer is written. Rules such as pattern, format, minLength and number ranges are checked afterwards when strict is true; an answer that breaks them is regenerated once.

When it fails

Result	Meaning	What to do
finish_reason: "length"	The JSON was cut off	Raise max_tokens or ask for less
502 invalid_structured_output	The answer failed the check twice	Retry; simplify the schema if it repeats
400 unsupported_schema	The schema can’t be used	Change the schema; retrying won’t help

A structured answer must finish within 300 seconds. The schema is also part of the prompt, so a very large schema leaves less room for your content.