JSON Schema Generator

JSON Schema is a vocabulary for annotating and validating JSON documents. It defines the expected structure, types, and constraints of your JSON data — like a contract or blueprint. JSON Schema is used for: API validation (OpenAPI/Swagger specs), form generation in UI frameworks (React JSON Schema Form), configuration file validation (VS Code settings, ESLint configs), automated testing (validating API responses), and documentation (describing your data model). Instead of writing schemas by hand, this tool generates them automatically from example data.

Draft 2020-12 is the latest and most feature-rich version, recommended for new projects. Draft 07 is the most widely supported across tools and libraries — use it if your toolchain does not yet support 2020-12. Draft 04 is legacy but still used by some older systems (including some OpenAPI 3.0 implementations). The generated schema is functionally similar across versions — the main differences are the $schema URI and availability of newer keywords.

The tool automatically detects: date-time (ISO 8601, e.g., "2024-01-15T10:30:00Z"), date ("2024-01-15"), time ("10:30:00"), email ("user@example.com"), URI ("https://example.com"), IPv4 ("192.168.1.1"), IPv6 ("::1"), and UUID ("550e8400-e29b-41d4-a716-446655440000"). Format annotations help validators and UI generators understand the semantic meaning of string fields.

If all items in an array are the same type (e.g., all strings or all integers), the schema uses a single "items" definition. If items are objects with different shapes, the tool merges their schemas to create a comprehensive item definition that covers all possible fields. If items are fundamentally different types (e.g., strings mixed with numbers), the tool uses the "oneOf" keyword to describe all possible item schemas.

When set to false, "additionalProperties" means the JSON object must contain only the properties defined in the schema — any extra properties will fail validation. This creates strict validation. When set to true (or omitted), additional properties beyond those listed in the schema are allowed. Use false for strict API contracts and configuration validation; use true for extensible data models.

Yes. The generated JSON Schema is compatible with OpenAPI 3.1 (which uses JSON Schema Draft 2020-12 natively) and can be adapted for OpenAPI 3.0 (which uses a subset of JSON Schema Draft 04). For OpenAPI 3.0, use the Draft 04 version option and you may need to remove the $schema property. The schema can be placed directly in the "components/schemas" section of your OpenAPI spec.

The generator infers the schema from one sample of data, and since every key is present in that sample, it lists them all in the 'required' array. Real data usually has optional fields, so after generating, edit the 'required' array to keep only the keys that must always be present, and remove the rest (a property not listed in 'required' is treated as optional). If you want the schema to reflect optionality automatically, feed it a sample that omits the optional fields — but hand-editing the required array is the precise, reliable way to express your actual contract.

A generated schema captures structure and types but not business rules — those you add by hand, and JSON Schema has rich vocabulary for them. For numbers use minimum/maximum (or exclusiveMinimum/Maximum); for strings use minLength/maxLength and pattern (a regex, e.g. for a phone format); for fixed sets use enum ("status": { "enum": ["active", "inactive"] }); for arrays use minItems/maxItems/uniqueItems. Generate the structural skeleton with this tool, then layer these constraints onto the fields that need them. That two-step approach — generate the shape, hand-add the rules — is the normal workflow.