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CORS Header Checker
x402
CORS Header Checker is a paid API for AI agents from cors-header-checker.underscoredone.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-12).
Sends a real HTTP request to a URL with a specified Origin header and returns all six standard CORS response headers plus a summary of whether cross-origin access is enabled and whether the tested origin is permitted.
Price / call$0.01
Success—
StatusUnknown
How this service works
Sends a real request to any URL you provide, attaches an Origin header, and reads back all six standard cross-origin permission headers the server returns. Tells you whether cross-origin requests are enabled at all, whether your specific origin is permitted, and shows every permission value exactly as the server sent it. Useful for finding why a browser is blocking a request, confirming a new deployment is configured correctly, or auditing whether a public API allows credentialed calls.
Output
A JSON object containing the target URL, HTTP status code of the probe request, a boolean cors_enabled flag, the tested origin string, an origin_allowed boolean, and the raw values of all six CORS headers (access-control-allow-origin, access-control-allow-methods, access-control-allow-headers, access-control-allow-credentials, access-control-expose-headers, access-control-max-age) exactly as the server returned them, plus any error message if the request failed.
Example use cases
Example prompt
“Can you check whether https://api.stripe.com allows cross-origin requests from https://myapp.com — specifically whether that origin is permitted and whether credentialed requests are allowed?”
Technical details
Endpoint
POSThttps://cors-header-checker.underscoredone.com/check?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need to know the exact CORS headers a live server returns at runtime, rather than inferring from documentation. It is ideal for debugging browser CORS errors, post-deployment verification of CORS configuration, or auditing third-party APIs for cross-origin policy compliance. Prefer it over manual curl commands when you need the result programmatically with parsed fields like cors_enabled and origin_allowed.
Side effects
- Target URL is unreachable or times out — error field contains the failure reason
- URL is malformed or missing http/https prefix — request rejected before being sent
- Target server returns no CORS headers — cors_enabled will be false and all header values null
- Network-level block prevents the probe from reaching the target — error populated
- Origin parameter is omitted — defaults to https://example.com which may not reflect real-world behavior
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| url | string | The full web address of the endpoint you want to check — must start with http:// or https://. |
| origin | string | The website address you want to test cross-origin access from, for example https://myapp.com. Defaults to https://example.com if you leave it out. |
Output
Schema · Response
{
"type": "json",
"example": {
"url": "https://api.github.com",
"error": "",
"status": 200,
"headers": {
"access-control-max-age": null,
"access-control-allow-origin": "https://github.com",
"access-control-allow-headers": null,
"access-control-allow-methods": null,
"access-control-expose-headers": "ETag, Link, Location, Retry-After, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Used, X-RateLimit-Resource, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval, X-GitHub-Media-Type, X-GitHub-SSO, X-GitHub-Request-Id, Deprecation, Sunset",
"access-control-allow-credentials": null
},
"api_version": "1.0.0",
"cors_enabled": true,
"origin_tested": "https://myapp.com",
"origin_allowed": false
}
}Tags
x402
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