ZeroTool Workbench

OpenAPI Validator

Validate OpenAPI 3.0 and 3.1 specs online in YAML or JSON. Check Swagger/OpenAPI structure, required fields, paths, responses, and spec summary.

100% Client-Side Your data never leaves your browser Free · No Sign-Up

Related Tools

JWT Decoder Decode and inspect JWT header, payload, and signature. Highlights expiry status and timestamp claims. HTTP Status Codes Searchable reference for all HTTP status codes (1xx–5xx) with descriptions and use cases. HMAC Generator Generate HMAC signatures using SHA-256, SHA-384, or SHA-512. Hex and Base64 output. Runs entirely in your browser. cURL to Code Converter Convert cURL commands to Python, JavaScript, Go, PHP, and Node.js code instantly. TOTP Generator Generate RFC 6238 TOTP codes with live countdown. Configurable algorithm, digits, and period. Includes QR code. JSON Schema Validator Validate JSON data against a JSON Schema online. Supports Draft-07 and Draft 2020-12. Shows error paths and detailed messages. 100% client-side.

OpenAPI Validator Online

Paste an OpenAPI 3.0 or 3.1 document in YAML or JSON and validate the structure before sharing it with frontend teams, API gateways, SDK generators, or documentation tools. The validator highlights missing required fields, invalid paths, and operations without responses.

How to Use

  1. Paste your OpenAPI spec (YAML or JSON) into the editor.
  2. Click Validate or press Ctrl+Enter.
  3. If valid, a summary panel shows the API title, version, path count, and operation count.
  4. If invalid, each error is listed with its JSON path and a description.

Required OpenAPI 3.x Fields

  • openapi — version string, e.g. “3.0.3” or “3.1.0”
  • info.title — human-readable API name
  • info.version — API version, e.g. “1.0.0”
  • paths — map of path item objects; each key must begin with /

Common Mistakes

  • Using Swagger 2.x format (swagger: “2.0”) instead of OpenAPI 3.x — migrate by replacing swagger with openapi: “3.0.3” and updating definitions to components/schemas.
  • Missing responses object inside an operation — every operation must declare at least one response.
  • Path keys that do not begin with / — all paths must be absolute, e.g. /users/{id}.
  • YAML indentation errors — use the YAML Validator to fix syntax issues first.

FAQ

What OpenAPI versions does this tool support?

The validator supports OpenAPI 3.0.x and 3.1.x specifications. Swagger 2.x (OpenAPI 2.0) documents will show a version warning with a migration tip.

Can I validate YAML and JSON specs?

Yes. Paste either YAML or JSON — the tool auto-detects the format and parses it before validation.

What does the validator check?

Required top-level fields (openapi, info, paths), info object fields (title, version), path format (must start with /), and that each operation has a responses object.

Is my API spec sent to any server?

No. All validation runs entirely in your browser using JavaScript. Nothing is transmitted to any server.

What are the required fields in an OpenAPI 3.x document?

openapi (version string), info.title, info.version, and paths. The servers, components, tags, and externalDocs fields are optional.