Validate OpenAPI Specs And Preview API Docs
OpenAPI (formerly Swagger) is the standard format for describing REST APIs. An OpenAPI spec defines your endpoints, request parameters, response shapes, and authentication in JSON or YAML. This tool validates whether a spec conforms to OpenAPI 3.x or Swagger 2.0 rules — catching missing required fields, invalid schema references, and structural errors that would cause code generators, API gateways, or documentation pipelines to fail. It also renders an interactive API documentation preview from the same pasted spec for Swagger 2.0 and OpenAPI 3.0/3.1, so you can check the structure and output in one step before publishing or handing it to another team.
How to use OpenAPI & Swagger Validator
Paste content into the openapi or swagger input panel.
Run the validator to check for success messages, syntax issues, or invalid structure.
Review the result, then copy or download it if you need to share the outcome.
Why this helps in real workflows
An API specification should be checked before publishing docs or sending it to another team.
A Swagger or OpenAPI file fails in a gateway, code generator, or mock server and you want to confirm whether the spec itself is valid.
A spec edited by hand in YAML or JSON should be validated before it is committed.
You want one page that can validate the spec and show what the API documentation preview will look like.
Which tool should you choose?
OpenAPI Validator & Docs Preview: Choose this when you want version-aware API spec validation plus a readable API documentation preview from the same pasted spec.
JSON Validator: Choose JSON Validator when you only want to confirm that pasted JSON syntax is valid.
YAML Validator: Choose YAML Validator when you only want to check YAML syntax without OpenAPI rules.
Common problems and fixes
The file is valid JSON or YAML, but another API tool still rejects it.
OpenAPI validation checks the API description itself, not just the raw JSON or YAML syntax.
You are not sure whether the file is Swagger 2.0 or OpenAPI 3.x.
The validator detects the version from the document and validates it accordingly.
The validation output is hard to act on.
This tool returns a plain-language result with the main issues and their document locations when available.
You want to see what the API docs will look like before publishing them.
Use the built-in docs preview section to inspect the generated API reference from the same spec you validate.
Related tools
Related Guides
Frequently asked questions
Can I validate Swagger 2.0 files here?
Yes. The validator supports Swagger 2.0 and OpenAPI 3.x documents. It detects the version automatically from the document structure — paste either format and the validator applies the correct ruleset.
What is the difference between an OpenAPI spec and a Swagger spec?
Swagger was the original name for the API description format. In 2016, the spec was donated to the OpenAPI Initiative and renamed OpenAPI. Swagger 2.0 is still widely used and fully supported here. OpenAPI 3.0, 3.1, and 3.2 are the current versions and include improvements to schema definitions, link objects, and webhook support.
Does this validate OpenAPI 3.1 and 3.2?
Yes. The validator handles OpenAPI 3.1 and 3.2 documents, including 3.1's full JSON Schema alignment and 3.2 additions. Paste the spec and the validator identifies the version from the openapi field and applies the matching rules.
My spec is valid JSON or YAML but another tool still rejects it — why?
JSON and YAML validators only check syntax. An OpenAPI validator checks the API description itself — required fields like info.title and info.version, valid path formats, correct response structure, and schema reference integrity. A spec can be syntactically valid JSON while still failing OpenAPI rules.
Can I preview API documentation from the same spec?
Yes, for Swagger 2.0 and OpenAPI 3.0/3.1 specs. After pasting and validating, the API docs preview section renders an interactive reference from the same input so you can verify the endpoint layout, parameter documentation, and response shapes before publishing or sharing the spec. OpenAPI 3.2 validation is supported, but the preview is not yet available for 3.2 specs.
Does this tool validate multi-file OpenAPI projects?
This tool is designed for a single pasted document. Multi-file projects that use $ref to reference external files will validate the main document structure, but external references will not be resolved. Combine the spec into a single file first for a complete validation pass.