JSON Schema Generator

About JSON Schema generator

The JSON Schema generator infers a draft 2020-12 schema from one example document. It records types, marks the keys it saw as required, and recognizes common string formats such as dates, emails, URLs and UUIDs. The result is a solid first draft of a contract you can tighten by hand for validation or API documentation.

How to use it

1. Paste a representative JSON sample into the JSON box.
2. Enter an optional Schema title, such as Product.
3. Decide whether Mark present keys as required (on by default) and Infer enums from repeated strings (off by default) should be enabled.
4. Review the JSON Schema output, then Copy it or use Download schema to save schema.json.

Types and formats from a product record, title Product

{"id":1,"price":9.99,"email":"a@b.co","created":"2024-05-01T10:00:00Z","nick":null}

(the $schema line naming draft 2020-12 comes first, then) "title": "Product", "type": "object", properties id = integer, price = number, email = string with format email, created = string with format date-time, nick = null, and "required" listing all five keys.

When to use it

• Creating a first-pass schema for request validation in an API project.
• Documenting the structure of a webhook payload for a partner.
• Producing a schema to feed into a form generator or editor.
• Spotting inconsistent types across records in a sample dataset, because they appear as anyOf.

Questions about JSON Schema generator

How does it tell integer from number?

By the parsed value. Anything that is a whole number is an integer, including 5.0, since JSON parsing does not preserve the trailing zero. A value with a fractional part becomes number.

Which string formats are detected?

date-time, date, email, uri for http and https addresses, and uuid. A string that matches none of those is a plain string with no format keyword.

When are enums produced?

Only for arrays made up entirely of strings, with ten or fewer distinct values, and only when at least one value repeats. Single string properties never receive an enum.

What happens with arrays of mixed items?

Objects inside an array are merged into one shape, and a key is required only if every item has it. Items of differing types, such as an integer and a number, are combined under anyOf.

What does switching required off do?

The generated schema contains no required lists at all, so every property becomes optional. Use it when your sample is only one possible example of a looser structure.

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