JSON Schema To OpenAPI Schema

Convert JSON Schema to OpenAPI 3.0 Schema Objects

OpenAPI 3.0 and JSON Schema are closely related but not identical. Keywords like $schema, patternProperties, and nullable type arrays (type: ["string", "null"]) are valid in JSON Schema but need adjustment for OpenAPI 3.0 Schema Objects. This tool automates that conversion so you can reuse JSON Schema as the single source of truth for API contracts.

What this tool does

Paste a JSON Schema Draft 04 document in the input panel. The converter maps it to an OpenAPI 3.0 Schema Object: nullable unions become nullable: true, unsupported keywords are renamed or transformed, and nested structures including allOf are preserved. Output updates automatically as you edit.

Why convert JSON Schema for OpenAPI 3.0?

OpenAPI 3.1 aligns closely with modern JSON Schema, but many teams still publish OpenAPI 3.0 specs. Hand-editing every schema difference is slow and error-prone. Automated conversion keeps validation rules in JSON Schema while producing Swagger-compatible schema objects for documentation generators and SDK tooling.

Common use cases

• Embed JSON Schema validation rules into an existing OpenAPI 3.0 specification.
• Migrate backend validation schemas into API documentation without duplicating definitions.
• Normalize nullable type arrays and pattern properties for Swagger UI and codegen tools.
• Preview how a JSON Schema will look inside an OpenAPI components section.

Related tools

Generate JSON Schema from sample JSON with the JSON to JSON Schema Generator, validate payloads with the JSON Validator, or format output with the JSON Formatter.