OpenAPI Formatter & Validator
Validate OpenAPI 3 and Swagger 2 documents, then format them as readable JSON or YAML. · Updated
OpenAPI and Swagger documents are the contract between frontend, backend, and generated clients. Validating and formatting specs locally keeps private internal endpoints and examples off third-party uploaders. Switch JSON/YAML output for tooling compatibility, use snippet mode for a starter fetch/axios/python call, and pair with YAML→JSON when you need a generic config converter.
Common errors and fixes
Missing OpenAPI or Swagger version
Start with openapi: 3.x.x or swagger: "2.0" at the document root.
Missing info.title or info.version
Add info.title and info.version — both are required for a valid specification.
No paths defined
Include at least one entry under paths (for example /health with an operation).
YAML/JSON parse failure
Fix indentation or trailing commas before validation. Use the YAML→JSON companion for intermediate debugging.
Options
| Option | Description |
|---|---|
| Output format | Choose the formatted document output. |
| Result mode | Format the full specification or generate a starter request for its first endpoint. |
| Client language | Language used for the generated starter request. |
| JSON indent | Number of spaces used when JSON output is selected. |
FAQ
Which API specifications are supported?
The tool checks OpenAPI 3.x and Swagger 2.0 documents for required top-level metadata and paths.
Can I convert OpenAPI YAML to JSON?
Yes. Paste YAML or JSON and select JSON output to create a formatted JSON document.
What does validation check?
It checks the specification version, info.title, info.version, and that at least one API path exists.
Can I format Swagger 2.0 documents?
Yes. Swagger 2.0 documents are accepted alongside OpenAPI 3.x documents.