JSON to Schema

Generate JSON Schema from a real JSON sample. Types and fields are inferred locally — good for validating APIs and writing Structured Output.

When the response exists and the docs come later, writing properties by hand is slow. Paste a sample, click Generate Schema, and keys that appeared become string, number, boolean, array, or object.

The auto draft often marks every sample key required and writes no descriptions. Before you ship, check nullable fields and extra fields yourself.

Inference runs in the browser. User data in the sample never leaves the device.

Treat it as a first draft

Inferring from a real response is closer to production than inventing a Schema. It cannot see optional fields that were absent, or business enum ranges.

Edit these three first

Check required, whether numbers are number or integer, and whether objects need additionalProperties: false. Get those wrong and Validate plus Structured Output go wrong together.

How to use it

Paste a real JSON sample, or load a sample.
Click Generate Schema and read the inference on the right.
Drop keys that should not be required; add description and format.
Accept a second real response on the Schema validate page.
For models or frontend, continue to Structured Output or Zod.

When to use it

Draft a JSON Schema quickly from one API response.
Prepare a core Schema for Structured Output, then wrap it per platform.
When you align fields with backend, start with a machine-readable type list.
Use the result as the input shape for Mock / Batch mock.

Keep in mind

It only sees the sample you pasted. Absent fields do not become optional on their own.
Arrays are usually inferred from the first few items. Mixed types get flattened or widened.
Don't treat an auto Schema as the production contract. Validate it with another payload first.

FAQ

Can I ship an auto-generated Schema as-is?

Not as the final draft. Add descriptions, check number types, and accept it with another real payload.

Why are so many fields required?

Inference only sees keys that appeared in the sample. Missing fields are not marked optional — you change that for the business.

How is this different from Structured Output?

This page produces generic JSON Schema. The Structured Output page wraps it for OpenAI / Gemini / Claude / MCP.

Does the data leave the browser?

No. Generation stays local.

Are nested objects supported?

Common nesting and arrays, yes. Very deep or cyclic structures should be split into multiple definitions.

Does it recognize email and uri?

Some strings look like emails or links. Still add format yourself — don't rely on the guess.

How is null inferred?

A null sample does not carry enough type info. Generate from a real value, or write a type array by hand.

How does this work with the OpenAPI page?

Get the core Schema here, then export doc YAML on the OpenAPI page.