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CORS Header Generator & Policy Builder

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CORS Header Builder

Visual generator and tester for CORS headers with Express, Next.js & Nginx configs.
Last updated: July 7, 2026•100% Client-Side & Private
INPUTJSON
INPUT

Paste or type your data here, or click "Load Sample" to try an example.

orOpen Fileor Drag & Drop
OUTPUTJSON

Ready: CORS Header Builder

Visual generator and tester for CORS headers with Express, Next.js & Nginx configs.

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About this Tool

Visual generator and tester for Cross-Origin Resource Sharing (CORS) headers and preflight configurations.

What is CORS and Why Do Preflight Errors Happen?

Cross-Origin Resource Sharing (CORS) is a browser security mechanism that restricts cross-origin HTTP requests. When front-end applications make requests with custom headers or methods like PUT/DELETE, browsers initiate an OPTIONS preflight request. If the server does not return matching Access-Control-Allow-* headers, the browser blocks the response.

One-Click Multi-Platform Export

Instantly generates compliant configuration snippets for Express.js, Next.js API routes, Nginx reverse proxies, Apache, and Cloudflare Workers.

Security Best Practices

Warns against using wildcard origins * simultaneously with Access-Control-Allow-Credentials: true, helping developers prevent dangerous CSRF vulnerabilities.

Privacy Guarantee

The CORS Header Generator & Policy Builder operates 100% locally in your web browser. Your inputs, configurations, and sensitive text payloads are processed entirely client-side using JavaScript and are never transmitted across the network or stored on any external servers.