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JSON Schema Generator & Validator — Free Online

Generate JSON Schema from sample data or validate JSON against a schema with this free online tool. Uses Ajv for validation. No sign-up required.

What is JSON Schema?

JSON Schema is a vocabulary defined by the IETF (Internet Engineering Task Force) that allows you to describe the structure, constraints, and validation rules for JSON data. A JSON Schema specifies which properties an object must have, what data types are allowed, value ranges, string patterns, array lengths, and more. It is widely used for API request/response validation, form generation, configuration file validation, and data documentation. JSON Schema supports drafts from Draft-04 through Draft 2020-12. This tool lets you automatically generate a JSON Schema from sample JSON data (useful as a starting point) and validate any JSON document against a schema using the Ajv (Another JSON Validator) library, which is the most widely used JSON Schema validator in the JavaScript ecosystem.

How to Use This Free Online JSON Schema Tool

  1. Choose between 'Generate Schema' and 'Validate JSON' using the tabs at the top.
  2. To generate a schema: paste a sample JSON object into the input area. The tool automatically infers types and generates a JSON Schema you can use as a starting point.
  3. To validate JSON: paste the JSON data you want to validate in the first field, and paste the JSON Schema in the second field. Click the 'Validate' button.
  4. Review the validation result: a green message means the JSON conforms to the schema; a red message lists all validation errors with their paths.
  5. Click the Copy button to copy the generated schema or validation results.

Common Use Cases for JSON Schema

  • API contract validation — Define JSON Schemas for your API request and response bodies to ensure clients send valid data and servers return expected structures.
  • Configuration file validation — Create schemas for application configuration files to catch errors early — before they cause runtime failures in production.
  • Generating schemas from examples — Quickly bootstrap a JSON Schema from sample data instead of writing one from scratch. Refine the generated schema by adding constraints like required fields and patterns.
  • Form generation and validation — JSON Schema is used by libraries like react-jsonschema-form and vue-jsonschema-form to automatically generate UI forms with built-in validation.
  • Data pipeline quality checks — Validate incoming data in ETL pipelines against a schema to reject malformed records before they corrupt your data warehouse.

FAQ

Which JSON Schema draft does this tool support?
The validation engine (Ajv) supports JSON Schema Draft-07 by default, which is the most widely adopted draft. The schema generator produces schemas compatible with Draft-04 and later. For Draft 2019-09 or 2020-12 features, you may need to add the ajv-formats or ajv-keywords plugins.
How accurate is the auto-generated schema?
The generated schema infers types from the sample data you provide — it determines string, number, boolean, array, and object types accurately. However, it cannot infer constraints like minimum/maximum values, string patterns (regex), required fields, or enum values. Treat the generated schema as a starting point and refine it manually.
What does 'allErrors: true' mean in the validation?
By default, Ajv stops at the first validation error. With 'allErrors: true', it continues checking and reports every error it finds, giving you a complete picture of all issues in one pass. This is more useful for debugging but slightly slower for very large documents.
Is this tool free and private?
Yes. Schema generation and validation run entirely in your browser using the to-json-schema and Ajv JavaScript libraries. No data is sent to any server, and no sign-up is required.

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