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A browser-based cors config helper tool. No data sent to server.

📘 How to Use

  1. Set the allowed origin, HTTP methods, and custom headers
  2. Choose your server environment to generate the configuration code

CORS Config Helper

Enter * to allow all domains.

Allow Credentials Cookie / Authorization header
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CORS Config Generator｜Fix Cross-Origin Errors with Server-Side Headers


A simple, interactive tool for developers to generate the correct server-side headers needed to resolve Cross-Origin Resource Sharing (CORS) errors. Instantly create configuration snippets for Nginx, Apache, Express.js, and Go.


💡 Tool Overview


This generator simplifies the often-frustrating process of configuring CORS policies by providing ready-to-use code blocks based on your specific requirements.


    

  • Multi-Platform Support: Generates valid syntax for popular server environments including Nginx (add_header), Apache (.htaccess), Express (res.header), and native Go (net/http).
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  • Real-Time Generation: The configuration code updates instantly as you adjust origins, methods, headers, or credential settings.
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  • Customizable Policies: Easily define which domains (origins), HTTP methods (GET, POST, etc.), and custom request headers are permitted.
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  • Credential Handling: Includes an option to enable Access-Control-Allow-Credentials for requests involving cookies or authorization headers, with built-in validation to prevent common misconfigurations.
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🧐 Frequently Asked Questions


Q. Why can't I use Allow-Credentials with a wildcard (*) origin?


A. This is a security restriction built into the CORS specification. When a request is made with credentials (like cookies or an Authorization token), the server response must specify the exact origin that is allowed. Using a wildcard (*) is too permissive and would create a security vulnerability, so browsers will reject the response. This tool enforces that rule by disabling the credential header in the generated code if the origin is set to *.


Q. What is a preflight OPTIONS request?


A. For "non-simple" requests (e.g., those using methods other than GET/POST, or with custom headers), the browser automatically sends a preliminary OPTIONS request to the server. This "preflight" request asks for permission before sending the actual request. The server must respond to the OPTIONS request with the correct CORS headers (like Access-Control-Allow-Methods and Access-Control-Allow-Headers) to confirm that the subsequent request is safe to send. The generated code for Express and Go includes logic to correctly handle these preflight requests.


📚 CORS Technical Deep Dive


When implementing a CORS policy that allows multiple specific origins (rather than a single origin or a wildcard *), it's crucial to include the Vary: Origin header in your server's response. This header tells proxies and browsers that the content of the response may differ depending on the Origin header of the incoming request. Without Vary: Origin, a cache might incorrectly serve a response intended for https://site-a.com to a user from https://site-b.com, potentially causing your application to fail. While this generator produces the core Access-Control-* headers, remember to add Vary: Origin to your server configuration for robust, cache-friendly CORS implementations.