What is JSON Schema?
JSON Schema is a declarative language for annotating and validating JSON data. Think of it as a contract: it says "this field must be a string, that one an integer, and these three are required." Common use cases:
- API validation — validate request and response bodies in Express, FastAPI, or any framework with JSON Schema support.
- Form generation — libraries like react-jsonschema-form and Formly generate UI forms from a schema.
- Documentation — OpenAPI (Swagger) uses JSON Schema to describe data models.
- Config validation — validate CI/CD configs, settings files, and infrastructure-as-code templates.
How this generator works
Paste a JSON example and the tool infers the schema:
- Type inference — each value is classified as string, integer, number, boolean, null, object, or array.
- Format detection — strings that look like emails, dates, URIs, UUIDs, or IPv4 addresses get a
formatannotation. - Required fields — by default, all keys at each level are marked required. For arrays of objects, only keys present in every item are required.
- Array merging — if your array contains objects with different shapes, the schemas are merged into a single item schema.
The output conforms to JSON Schema Draft 2020-12.
Tips for better schemas
- Use realistic sample data. The tool infers from what it sees — if a field is always an integer in your sample, it'll be typed as integer.
- Include edge cases in arrays. Pass multiple objects with different optional fields so the tool correctly marks some as optional.
- Review and refine. The generated schema is a starting point. Add
minLength,pattern,enum, ordescriptionfields manually for production use.
Related JSON tools
- JSON Formatter — format, validate, and minify JSON.
- JSON Viewer — explore JSON as an interactive tree.
- JSON to TypeScript — generate TypeScript interfaces from JSON.
- YAML Validator — validate YAML syntax with error line numbers.