OpenAPI Spec Viewer

OpenAPI (formerly Swagger) is the industry-standard specification for describing RESTful APIs. Swagger was the original name when SmartBear owned it. In 2016, the spec was donated to the OpenAPI Initiative and renamed to OpenAPI Specification (OAS). Today 'Swagger' often refers to the tooling (Swagger UI, Swagger Editor), while 'OpenAPI' refers to the spec itself. OpenAPI 3.0 was a major redesign over Swagger 2.0, introducing cleaner request body handling, multiple server support, and better component reuse.

This viewer is optimized for OpenAPI 3.0.x and 3.1.x specs. It also renders many Swagger 2.0 (OAS 2) documents since the core path/operation/schema structure is similar, though some OAS 2-specific fields like 'definitions' (vs 'components/schemas') and 'produces'/'consumes' are not fully parsed. For best results, use an OpenAPI 3.x spec.

Both formats are supported. The viewer auto-detects the format: if your input starts with '{' it is treated as JSON and parsed with JSON.parse. Everything else is treated as YAML and processed with the built-in YAML parser. The YAML parser handles all OpenAPI-relevant constructs including nested mappings, sequences, block scalars, and inline values.

The color coding follows REST conventions: GET (green) retrieves data without side effects; POST (blue) creates a new resource; PUT (yellow) replaces a resource entirely; PATCH (orange) partially updates a resource; DELETE (red) removes a resource. HEAD and OPTIONS use gray as they are utility methods. These colors help you quickly identify the intent and safety characteristics of each endpoint.

$ref is OpenAPI's way of referencing a schema defined elsewhere in the document, such as '#/components/schemas/User'. This avoids duplication and keeps specs maintainable. This viewer resolves $ref references inline when rendering endpoint details and schema tables — so instead of showing the raw $ref string, it follows the reference and displays the actual property list. Only local $ref references (within the same document) are resolved.

Most frameworks have libraries that auto-generate OpenAPI specs from your code. For Node.js: fastify-swagger, tsoa, or @nestjs/swagger. For Python: FastAPI generates specs automatically; Flask/Django can use flask-smorest or drf-spectacular. For Go: swaggo/swag. For Java/Kotlin: springdoc-openapi or swagger-core. Alternatively, write your spec first using the OpenAPI 3.x specification directly in YAML — this 'API-first' approach is recommended for better design consistency.