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JSON Schema Generator

Create a JSON Schema from a sample document.

Root name: Mark missing keys optional

How to Use

Paste a sample JSON document into the left box.
JSON Schema is already chosen.
Keep Mark missing keys optional on to leave varying keys out of required.
Copy the schema and refine it: add formats, patterns or limits where you need them.

Frequently Asked Questions

Which draft is used?

Draft 2020-12, the current version, which validators such as Ajv support.

How is required decided?

Every key present in all sampled items is required; keys missing from some items are left out when Mark missing keys optional is on.

Are formats such as email or date-time added?

No. A sample cannot prove a format, so strings stay plain strings; add format where you know it.

Is my JSON sent anywhere?

No. The schema is generated in your browser.

Generate a JSON Schema from a Sample

Updated September 30, 2026 · By Saman

A JSON Schema lets any language validate data against the same rules. This page opens JSON to Types with JSON Schema chosen, as a starting point you can refine.

Nullable values

A field that is null in one sample and a string in another gets "type": ["string", "null"], the standard way to allow both.

Related tools

To check the sample is valid JSON first, use the JSON formatter. For typed code instead of a schema, see JSON to TypeScript.

Guides

How to Type an API Response in TypeScript fetch gives you data typed as any, which switches TypeScript off exactly where bugs come from. Here is how to give API data a real type, quickly and safely.

JSON Schema Generator

Generate a JSON Schema from a Sample

Nullable values

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