OpenAPI Spec Validator Online
Catch schema errors, missing responses, and broken references before they reach production. Our OpenAPI spec validator online checks OpenAPI 3.0, 3.1, and Swagger 2.0 definitions in your browser — no uploads, no signups, no server round-trips. Whether you are shipping a new API contract or auditing a legacy Swagger file, this free OpenAPI validator flags structural issues, security gaps, and documentation gaps instantly.
What Does an OpenAPI Validator Check?
| Check Type | What It Detects | Severity |
|---|
| Schema structure | Missing openapi or swagger field | Error |
| Info object | Missing title, version, description | Warning |
| Paths | Empty paths object or missing methods | Warning |
| Operations | Missing operationId or responses | Warning / Error |
| Responses | Missing success status codes | Warning |
| Security | Missing security scheme definitions | Warning |
| Servers | No server URLs configured | Info |
| Tags | Unused or missing tags | Info |
Related Keywords
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OpenAPI vs Swagger
| Aspect | OpenAPI | Swagger |
|---|
| Version | 3.0, 3.1 | 2.0 |
| Maintainer | OpenAPI Initiative | SmartBear |
| Schema | JSON Schema Draft 7+ | Swagger Schema |
| Links | link object | Vendor extensions |
| Security | Security Scheme Object | Security Definition Object |
| Webhooks | Supported | Not supported |
Our validator supports both formats.
Common Validation Errors
| Error | Cause | Fix |
|---|
| Missing info.title | API contract has no title | Add info.title string |
| Missing responses | Path operation lacks responses map | Add 200/201 responses |
| Invalid JSON | Syntax error in spec | Validate JSON.parse first |
| Unused schema | Component defined but never referenced | Remove or reference in paths |
| Wrong media type | application/xml instead of application/json | Standardize content types |
Best Practices
| Practice | Why |
|---|
| Include description | Helps consumers understand endpoints |
| Use operationId | Enables SDK generation and tooling |
| Define servers | Clients know where to send requests |
| Add tags | Organize operations in docs |
| Version your API | Prevents breaking changes |
| Use securitySchemes | Document auth requirements |
Supported Specifications
| Spec | Supported | Notes |
|---|
| OpenAPI 3.0 | Yes | Full validation |
| OpenAPI 3.1 | Yes | JSON Schema Draft 2020-12 |
| Swagger 2.0 | Yes | Legacy support |
| JSON | Yes | Only format accepted |
| YAML | Partial | Paste JSON only |
Conclusion
Our OpenAPI spec validator online gives you instant feedback on API contract quality. Whether you call it an OpenAPI validator, Swagger validator, or API specification checker, the goal is the same: ship safer API docs with fewer surprises. Paste your spec and validate it now — free, fast, and private.