CORS Headers Generator — Visual CORS Config Builder

CORS Headers Generator is a free, browser-based tool for building Cross-Origin Resource Sharing configuration visually. Configure your allowed origins, HTTP methods, request headers, credentials, and preflight cache settings — then copy the generated config for Express.js, Nginx, Apache, or raw HTTP headers. No sign-up, no install, no server-side requests.

The Problem

CORS errors are one of the most Googled front-end frustrations:

Access to fetch at 'https://api.example.com' from origin 'https://app.example.com'
has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present.

The fix is adding the right headers to your server — but the configuration surface is wide:

• Access-Control-Allow-Origin accepts exactly one origin or a wildcard (never a list)
• Credentials require an explicit origin — you can't combine * with credentials: true
• Preflight OPTIONS requests need their own response with the correct headers
• Nginx, Apache, Express, and raw HTTP all need different syntax for the same policy
• Multi-origin setups require server-side logic to reflect the requesting origin

Getting every piece right without a reference takes longer than it should. This tool makes it immediate.

How It Works

1. Configure Allowed Origins

Enter specific domains (https://app.example.com, https://admin.example.com) or toggle the wildcard to allow all origins. For multi-origin configurations, the Express.js output automatically generates the allowlist logic that reflects the matching origin back — since Access-Control-Allow-Origin only accepts a single value, the server must check and echo the requesting origin.

The tool also warns you in real time when you try to combine wildcard origins with credentials — browsers reject this combination.

2. Toggle HTTP Methods

Click to enable or disable any combination of GET, POST, PUT, DELETE, PATCH, OPTIONS, and HEAD. OPTIONS is automatically included when you configure preflight handling.

3. Define Allowed and Exposed Headers

Type or select from common headers (Content-Type, Authorization, X-API-Key, Accept) to build your Access-Control-Allow-Headers list. Separately configure Access-Control-Expose-Headers for headers your API sends that the browser should expose to client-side JavaScript.

4. Credentials and Preflight Max-Age

Toggle Access-Control-Allow-Credentials: true to allow cookies and session tokens to be sent cross-origin. Set the preflight cache duration (Max-Age) to reduce OPTIONS requests — 86400 seconds (24 hours) is a common production value.

5. Copy the Generated Config

Switch between four output tabs:

• Express.js — a complete corsOptions object ready to pass to the cors npm package, with multi-origin allowlist logic when needed
• Nginx — add_header directives for both the preflight OPTIONS block and normal responses
• Apache — mod_headers directives wrapped in <IfModule> blocks, with mod_rewrite handling for the OPTIONS preflight
• HTTP — raw Access-Control-* headers for any platform not covered above

Key Features

• Four output formats — Express.js, Nginx, Apache, and raw HTTP
• Multi-origin support — automatic allowlist logic in the Express.js output
• Real-time preview — configuration summary updates as you change settings
• Credential validation — warns when wildcard origin conflicts with credentials
• Common header suggestions — one-click add for Content-Type, Authorization, and others
• Preflight configuration — Max-Age and OPTIONS handling included in every format
• Fully client-side — no data leaves your browser
• No sign-up required — open, configure, copy, paste

Technical Implementation

Core Technologies

• Next.js with App Router
• TypeScript in strict mode
• Tailwind CSS for styling
• shadcn/ui component library
• Framer Motion for animations
• Client-side rendering — zero external API dependencies

Architecture

The tool maintains a typed CorsConfig state object (origins, methods, allowedHeaders, exposedHeaders, credentials, maxAge) and derives all four output formats as pure functions of that state. Every format generator runs synchronously on state change, so output updates without any debounce or async logic.

Multi-origin Express.js output is handled by generating an allowedOrigins array and a custom origin callback that uses Array.prototype.includes() — the correct pattern for reflecting origins while maintaining type safety.

Use Cases

Connecting a React or Vue App to an Express API

Your front-end on https://app.myproduct.com needs to call https://api.myproduct.com. Enter your origin, select the methods your routes use, add Authorization and Content-Type to allowed headers, and enable credentials if you're using cookies. Copy the Express.js output, paste it before your route definitions, and the CORS error disappears.

Configuring Nginx as a Reverse Proxy

When Nginx sits in front of your Node.js, Python, or Go backend, CORS headers belong in the Nginx config — not in application code. The Nginx output includes the if ($request_method = 'OPTIONS') block for preflight and the add_header directives for all other responses.

Fixing CORS on a Static Site with an External API

If your Jamstack site calls a third-party API that you control, you need CORS on the API server. The raw HTTP output gives you the header names and values directly, so you can add them in any language — Python's Flask, Ruby's Rack middleware, PHP headers, or a serverless function.

Staging and Production with Different Domains

Enter both your staging (https://staging.example.com) and production (https://app.example.com) origins. The Express.js output generates the allowlist check automatically, so the same server config works across environments without deploying separate configs.

Learning CORS From the Headers Up

Rather than starting with a framework abstraction, start with the raw HTTP headers to understand exactly what the browser checks. Then switch to the Express.js or Nginx tab to see how those headers map to server configuration.

Why CORS Headers Generator?

vs. Documentation and Stack Overflow

Documentation explains what each header does. Stack Overflow shows one-off examples. This tool generates the exact configuration for your specific combination of origins, methods, and headers — ready to paste without editing.

vs. Writing It by Hand

The multi-origin allowlist pattern, the OPTIONS preflight block, and the interaction between credentials and wildcard origins are all easy to get subtly wrong. The generator handles the edge cases correctly so your first paste is your working config.

vs. Framework Docs

Express's cors package documentation shows the option names. Nginx's docs show the directive syntax. Neither shows you the complete preflight handling block with correct origin reflection. This tool does.

Results

CORS Headers Generator removes the most common points of failure in cross-origin configuration:

• Origin handled correctly — single origin, wildcard, or multi-origin allowlist
• Preflight ready — OPTIONS handling generated for every format
• Credentials safe — warns before you create an invalid wildcard + credentials combination
• Format-appropriate output — Express syntax, Nginx directives, Apache directives, or raw headers

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Try it now: cors-headers-generator.tools.jagodana.com