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

CORS (Cross-Origin Resource Sharing) is a security mechanism that controls how web pages from one domain can access resources from another domain. Testing CORS is essential to ensure your API or web service is properly configured to allow legitimate cross-origin requests while maintaining security. This free CORS tester helps you verify that your CORS headers are correctly configured.

How do I fix CORS errors?

CORS errors typically occur when the server doesn't send proper Access-Control headers. To fix them: 1) Ensure your server sends 'Access-Control-Allow-Origin' header with appropriate origins, 2) Add 'Access-Control-Allow-Methods' for methods you want to support, 3) Include 'Access-Control-Allow-Headers' for custom headers, and 4) For credentials, set 'Access-Control-Allow-Credentials' to true. Use this free CORS testing tool to verify your configuration.

What is a CORS preflight request?

A CORS preflight request is an OPTIONS request automatically sent by browsers before certain cross-origin requests. It checks whether the actual request is safe to send by verifying the server's CORS policy. Preflight requests are triggered by custom headers, methods other than GET/POST, or certain content types. Our free CORS tester can simulate preflight requests to help you debug CORS issues.

Can I test CORS with custom headers?

Yes! This free CORS testing tool allows you to add custom headers to your requests. Simply click 'Add Header', enter the header name and value, and test. This is useful for testing Authorization headers, Content-Type headers, and other custom headers that might trigger CORS preflight requests.

Is this CORS tester free to use?

Yes, this CORS testing tool is completely free to use with no subscriptions, registrations, or limitations. Test as many URLs as you need, add custom headers, and access all features without any cost. FreeWWW provides free tools and utilities for everyone!

Free Online CORS Tester (No Signup)

What is CORS Testing?

Cross-Origin Resource Sharing (CORS) is a security mechanism that controls how web pages from one domain can access resources from another domain. This free CORS testing tool helps you:

Test CORS policies for any URL or API endpoint
View all CORS-related headers returned by the server
Test different HTTP methods (GET, POST, PUT, DELETE, PATCH, OPTIONS)
Add custom headers to simulate real-world scenarios
Diagnose CORS issues with detailed explanations and recommendations
Track request timing and performance metrics
Save test history for future reference

Common Use Cases

Why is my frontend getting CORS errors? Enter your API URL and check which Access-Control headers the server returns — missing or misconfigured headers are the most common cause.
How do I verify my server's CORS configuration? Test with different HTTP methods and custom Origin headers to confirm your server responds with the correct allowed origins, methods, and headers.
How do I debug preflight request failures? Send an OPTIONS request to see if the server properly handles preflight checks and returns the required CORS headers.

🎯 Test Configuration

URL to Test

HTTP Method

Custom Headers (Optional)

Request Body (for POST, PUT, PATCH)

Include credentials (cookies)

🌐 CORS Tester

What is CORS Testing?

Common Use Cases

🎯 Test Configuration

📊 Test Results

🔑 CORS Headers

📋 All Response Headers

⚠️ CORS Issues & Recommendations

📄 Response Preview

📜 Test History