What is CORS and why do I need to check it?

CORS (Cross-Origin Resource Sharing) is a browser security mechanism that controls which websites can access resources on another domain. You need to check CORS because misconfigured settings can block legitimate requests to your API or cause security vulnerabilities. CORS Checker helps you verify these settings are correct and secure.

Why am I getting 'blocked by CORS policy' errors?

This error occurs when your browser blocks a cross-origin request because the server's CORS headers don't permit it. Common causes include the server not allowing your origin, missing Access-Control-Allow-Origin headers, or incorrect HTTP methods. Use CORS Checker to identify which specific CORS header is missing or misconfigured.

Is it safe to set Access-Control-Allow-Origin to *?

Setting Access-Control-Allow-Origin to * allows any website to access your resource, which creates a significant security risk. It's better to explicitly whitelist specific trusted origins. However, for public APIs that don't handle sensitive data, this setting may be acceptable. Always evaluate your security needs carefully.

Can CORS Checker test APIs that require authentication?

Yes, CORS Checker supports custom headers, allowing you to include authentication tokens, API keys, or authorization headers in your test requests. This enables you to check CORS configuration for protected endpoints that require credentials or special authentication mechanisms.

What's the difference between preflight and simple requests in CORS?

Simple requests (GET, POST with certain headers) are sent directly, while preflight requests (OPTIONS method) are sent first to check if the actual request is allowed. CORS Checker analyzes both types to ensure your server properly handles preflight requests and responds with appropriate CORS headers for actual requests.

CORS Checker

How to Use CORS Checker

When to Use CORS Checker

Technical Information

Frequently Asked Questions