Reliable Structured JSON Output Pattern

Get valid, schema-conforming JSON from any model using native structured outputs where available, and validate-and-repair otherwise.

jsonschemavalidationextraction

Setup time30 minutes (estimate)

Estimated costRepairs add an extra call only on failures.

ToolsPython

VerificationNot yet independently verified

Order of preference

Native structured outputs (e.g. OpenAI response_format: {type: "json_schema", ...} with strict: true, or tool calling with a schema).
JSON mode plus schema in the prompt.
Prompt-only plus validation and a repair retry.

Prompt (fallback path)

Extract the fields below from the text. Return ONLY a JSON object matching this schema,
with no markdown fences or commentary. Use null for unknown values; do not guess.
Schema: {"name": string, "email": string|null, "company": string|null}
Text: """{{input}}"""

Validate and repair

import json, jsonschema

def get_json(call, prompt, schema, retries=2):
    msg = prompt
    for _ in range(retries + 1):
        raw = call(msg)
        try:
            data = json.loads(raw)
            jsonschema.validate(data, schema)
            return data
        except Exception as e:
            msg = f"{prompt}\n\nYour previous output was invalid: {e}. Return corrected JSON only."
    raise ValueError("Could not obtain valid JSON")