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CORS Tester & Inspector
Test Cross-Origin Resource Sharing (CORS) headers for any URL. Inspect Access-Control-* response headers, debug preflight OPTIONS requests, and verify CORS compliance.
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CORS Report for
CORS Result
Response Time
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HTTP Status
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Response Headers
| Header | Value |
|---|
No CORS-related headers found in the response. Add custom headers and retry, or check if the server supports CORS.
Preflight (OPTIONS) Request
A preflight request is automatically sent when the request includes custom headers, a non-simple method, or credentials. Below are the preflight results.
Select a request that triggers preflight (e.g., POST with custom headers) to see preflight results.
CORS Analysis
Run a test to see detailed CORS analysis.
Request Failed
What Is CORS?
Cross-Origin Resource Sharing (CORS) is a browser security mechanism that controls how web pages from one origin can request resources from a different origin. When a web application makes a cross-origin HTTP request, the browser adds an Origin header and checks the server's response for Access-Control-Allow-Origin and related headers before allowing the JavaScript to read the response.
This tool helps you debug CORS issues by sending test requests with custom origins, methods, and headers. It shows you exactly which Access-Control-* headers the server returns, automatically performs a preflight OPTIONS request when needed, and provides a clear pass/fail analysis explaining why a request would be allowed or blocked by the browser. Web developers and API integrators use CORS testing daily to debug integration issues between frontend applications and third-party APIs.
How to Use This CORS Tester
- Enter URL — Type or paste the target URL you want to test for CORS compliance.
- Configure request — Optionally set a custom origin (e.g.,
https://your-site.com), custom headers, request method, and credentials flag to simulate real browser behavior. - Click Test — Press Test to send the request. The tool inspects
Access-Control-*headers in the response and performs a preflight (OPTIONS) request when applicable. - Review results — The CORS report shows pass/fail status, response headers table, preflight results, and detailed analysis.
- Try examples — Use Valid Example for an API with open CORS (
api.github.com), or Invalid Example for a URL that blocks cross-origin requests.
Frequently Asked Questions
What does CORS stand for and why does it matter?
CORS stands for Cross-Origin Resource Sharing. It is a browser security feature that prevents web pages from making requests to a different origin than the one that served the web page. Without CORS, any website could read data from any other website, which would be a severe security vulnerability.
What is a preflight request?
A preflight request is an automatic OPTIONS request sent by the browser before certain cross-origin requests. It is triggered when the request uses a non-simple method (PUT, DELETE, PATCH), includes custom headers, or sends credentials. The browser only sends the actual request if the preflight succeeds.
What is the difference between simple and preflight requests?
Simple requests are GET, HEAD, or POST with limited Content-Type values and no custom headers — these can be sent without a preflight. All other cross-origin requests trigger a preflight OPTIONS request first.
What do the main CORS headers mean?
Access-Control-Allow-Origin specifies which origins are allowed (* = all origins). Access-Control-Allow-Methods lists permitted HTTP methods. Access-Control-Allow-Headers lists permitted request headers. Access-Control-Allow-Credentials indicates whether credentials are allowed.
Is my data sent to a server?
The test requests are sent from your browser directly to the target URL you specify. This website does not proxy or store any request data. The CORS analysis is performed entirely in your browser.
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