JSON schema

A formal description of the shape of a JSON document — keys, types, required fields, allowed values — used to constrain and validate model output.

Last updated: November 9, 2026 · Markdown version

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How to apply it in prompts

Use this concept to reduce ambiguity and improve consistency. If you need strict formatting, combine it with a JSON guide and a per-model template.

Strict JSON Models Packs

What it means

Definition: JSON Schema is a standard vocabulary for describing JSON: which keys exist, their types, which are required, enumerations, minimums and patterns.
Why it matters: it is the contract between the model and your code. Even a simplified schema pasted in the prompt (keys plus types) makes the output far more consistent.
How to apply it: in the prompt, give the schema, say 'return ONLY JSON' and say what to do with missing values (null, not a guess). Where the provider offers structured outputs, pass the schema there so the format is enforced at generation time.
In production, always validate the result against the schema and retry or reject on failure; never assume valid JSON means correct content.

Copy-paste example

Extract the order from the text. Return ONLY JSON that matches this schema:
{"orderId":"string","items":[{"sku":"string","qty":"number"}],"notes":"string|null"}
If a field is missing in the text, use null. Do not guess.

Text:
"""[paste]"""

Opens the analyzer with the prompt prefilled.

Open in Promptea

FAQ

Is the schema in the prompt enough to guarantee valid JSON?

It makes valid JSON likely, not certain. For guarantees use the provider's structured-output feature where available and validate the result in code.

Should I ask for markdown code fences around the JSON?

Not if a program reads it: say 'return ONLY JSON, no markdown' so the output can be parsed directly.