About JSON Schema Generator

Generate JSON Schema from a sample JSON object. Part of the DevTools Surf developer suite. Browse more tools in the Generators collection.

Use Cases

• Generating validation schemas from existing API responses
• Creating OpenAPI spec components from sample JSON payloads
• Building form validation rules from backend data models
• Documenting API contracts by inferring schemas from examples

Tips

• Paste a sample API response to auto-generate its schema
• Review inferred types and add constraints like min/max manually
• Use the generated schema for request validation middleware

Fun Facts

• JSON Schema was first proposed by Kris Zyp in 2009 and reached its most recent stable draft (2020-12) after 11 years of evolution.
• JSON Schema is used by the OpenAPI Specification (formerly Swagger) to define request and response body structures.
• The $ref keyword in JSON Schema enables schema composition, allowing reuse of type definitions across an entire API specification.

FAQ

What draft version does it output?

Draft 2020-12 by default (the current version). Toggle to Draft-07 for compatibility with older validators that haven't upgraded.

Does it detect types correctly?

Usually — primitives, objects, and arrays infer cleanly. Mixed-type arrays (sometimes strings, sometimes numbers) become anyOf. Null values make fields nullable.

Are required fields detected?

Yes — fields present in every sample record are required; fields missing from any record become optional. Small sample sizes can mislead — verify the output.

What about format hints?

Heuristics for common formats: ISO 8601 dates get `format: date-time`, email-shaped strings get `format: email`. Review and refine manually.