Swagger Validator API

Free Swagger/OpenAPI validator API with no key: check any OpenAPI or Swagger specification for schema errors by URL. Returns structured messages. Tested.

No API key requiredCORS enabledHTTPSFree tier

Endpoint tested and returned HTTP 200 on 20 Aug 2026

What is the Swagger Validator API?

The Swagger Validator API is a free, key-free service that validates an OpenAPI or Swagger specification against the official schema, returning structured error messages for any problems found.

An invalid OpenAPI specification breaks code generation, documentation rendering and client SDKs, often with confusing downstream errors. Validating the spec directly gives you a clear answer about where the problem actually is.

The success case is quietly counterintuitive: a valid specification returns `{"schemaValidationMessages": []}` — an empty array rather than any explicit confirmation. Code that checks for a success flag will find nothing; check the array length instead.

Quick facts

Base URL: https://validator.swagger.io/validator
Authentication: No API key required.
Rate limit: No published limit; intended for interactive and CI use.
Pricing: Free, provided by SmartBear.
CORS: Enabled — callable directly from browser JavaScript
Official docs: Read the docs

How to use the Swagger Validator API

Every request below was executed against the live API on 20 Aug 2026, and the response shown is the real body it returned — not an illustration.

1. Validate an OpenAPI specification

GET https://validator.swagger.io/validator/debug?url=https%3A%2F%2Fpetstore.swagger.io%2Fv2%2Fswagger.json

curl

curl 'https://validator.swagger.io/validator/debug?url=https%3A%2F%2Fpetstore.swagger.io%2Fv2%2Fswagger.json'

JavaScript (fetch)

const res = await fetch("https://validator.swagger.io/validator/debug?url=https%3A%2F%2Fpetstore.swagger.io%2Fv2%2Fswagger.json");
if (!res.ok) throw new Error(`Request failed: ${res.status}`);
const data = await res.json();
console.log(data);

Python (requests)

import requests

res = requests.get("https://validator.swagger.io/validator/debug?url=https%3A%2F%2Fpetstore.swagger.io%2Fv2%2Fswagger.json", timeout=20)
res.raise_for_status()
print(res.json())

Response — HTTP 200

{
  "schemaValidationMessages": []
}

Parameters

Parameter	Type	Required	Description
`debug?url=`	string	Optional	Validate a spec at a public URL, returning JSON messages. `url=https%3A%2F%2Fpetstore.swagger.io%2Fv2%2Fswagger.json`
`?url=`	string	Optional	Returns a validity badge image instead of JSON. `url=...`
`(POST body)`	body	Optional	POST the spec directly when it is not publicly hosted. `{...}`

Response fields

schemaValidationMessagesarray: Validation problems. An EMPTY array means the spec is valid.
...levelstring: error or warning.
...messagestring: What is wrong.
...schemaPath / instancePathstring: Where in the specification the problem occurs.

What you can build with the Swagger Validator API

Gate CI on OpenAPI specification validity
Debug why code generation from a spec is failing
Add a validity badge to API documentation
Check a third-party spec before building a client against it

Common errors and how to fix them

Empty response means success

A valid spec returns an empty messages array.

Fix: Check schemaValidationMessages.length === 0 rather than looking for a success flag.

Cannot validate a private spec by URL

The validator must be able to fetch it.

Fix: POST the specification body directly instead of passing a URL.

Warnings treated as failures

Some messages are level: warning.

Fix: Filter on level === 'error' if warnings should not fail your build.

Swagger Validator API — frequently asked questions

Is the Swagger validator API free?

Yes, free with no API key, provided by SmartBear.

How do I know if my spec is valid?

A valid specification returns an empty schemaValidationMessages array. There is no explicit success flag, so check the array length.

Can I validate a spec that isn't publicly accessible?

Yes, POST the specification body directly rather than passing a URL — the validator cannot fetch private endpoints.

Does it validate both Swagger 2.0 and OpenAPI 3?

Yes, it detects the version from the specification and validates against the appropriate schema.

Tools that pair with this API

JSON Formatter

Format, beautify and minify JSON online with 2-space, 4-space or tab indentation. Sort keys alphabetically and catch syntax errors instantly — free and private.

JSON Validator

Free online JSON validator: validate JSON and find syntax errors with the exact line and column. See root type, key counts and depth — instant and 100% private.

YAML to JSON Converter

Convert YAML to JSON online in your browser. Handles block scalars, flow collections, anchors and multi-document files — nothing is uploaded.

Alternatives to Swagger Validator API

If Swagger Validator does not fit, these developer & testing apis cover similar ground. Every one was called before publishing, and each links to its own reference page with a working curl command and the response it returned.

API	What it does	Auth	CORS	Last verified
GitHub REST API	GitHub REST API with no key for public data: repository details, users, issues, releases and commits. 60 req/hour unauthenticated, 5,000 with a token.	No key	Yes	19 Aug 2026
JSONPlaceholder	Free fake REST API for testing and prototyping. Posts, comments, users and todos with full GET, POST, PUT and DELETE support. No key. Real curl examples.	No key	Yes	19 Aug 2026
Postman Echo	Postman Echo reflects your HTTP request back as JSON: headers, body, query params and auth. Free, no key, ideal for debugging clients. Real POST example.	No key	No	19 Aug 2026
DummyJSON	Free fake REST API with realistic products, users, carts, recipes and auth. Supports search, pagination, sorting and POST. No key. Tested GET and POST examples.	No key	Yes	19 Aug 2026
Terraform Registry	Query the public Terraform Registry for modules and providers, with versions, download counts and source repositories. No API key. Verified example included.	No key	No	21 Aug 2026
unpkg	Free unpkg CDN with no key: fetch any file from any npm package by URL, including package.json, with version ranges and directory listings. Tested example.	No key	Yes	20 Aug 2026

All Developer & Testing APIs

Swagger Validator is an independent third-party service and is not affiliated with ByteTools or ByteVancer. Details on this page were verified on 20 Aug 2026; always check the official documentation before relying on this API in production, as terms and limits can change.