What Is JSON Schema?
JSON Schema is a declarative language for defining the structure and constraints of JSON data. It describes what fields are expected, what types they should be, which are required, and what values are acceptable. This makes it invaluable for API validation, configuration file checking, and data pipeline quality assurance.
Think of it as a contract between systems: a schema guarantees that the JSON data exchanged between a client and server, or between microservices, conforms to an agreed-upon structure. When data violates the schema, validation errors pinpoint exactly what went wrong.
Common Validation Keywords
Specifies the expected data type: string, number, integer, boolean, null, object, or array.
Lists which properties must be present in the object. Missing required fields trigger a validation error.
Restricts the value to a fixed set of allowed values. Useful for status fields, categories, or dropdown options.
Validates strings against a regular expression pattern. Use it for email formats, phone numbers, or custom identifiers.
When to Use JSON Schema
JSON Schema shines in any situation where data integrity matters. REST API endpoints can validate request bodies before processing. Configuration files can be checked at startup to catch typos before they cause runtime failures. Data pipelines can verify that upstream changes have not broken expected formats. Form builders can auto-generate validation rules from a schema definition.
Auto-Generating Schemas from Data
Writing schemas by hand can be tedious. This tool can analyze your existing JSON data and generate a complete schema automatically. It detects property types, identifies required fields (present in all objects), and creates definitions for nested structures. The generated schema is a great starting point that you can refine by adding constraints like minimum values, string patterns, or enum restrictions.
Frequently Asked Questions
What is JSON Schema?
JSON Schema is a vocabulary for annotating and validating JSON documents. It describes the structure, required fields, value types, and constraints of a JSON object.
Can this tool generate a schema from my JSON data?
Yes. Switch to the Generate tab and paste your JSON data. The tool will infer a complete JSON Schema from the structure.
What validation features are supported?
Type checking, required fields, enum, minLength/maxLength, minimum/maximum, pattern, and nested object/array validation.
What JSON Schema draft version does this use?
Generated schemas follow Draft 2020-12. The validator supports commonly used keywords from Draft 4 through 2020-12.
Is my data sent to a server?
No. All validation and generation happens in your browser. Your data never leaves your device.