CORS Header Generator

Generate secure Cross-Origin Resource Sharing (CORS) HTTP headers. Export instant configs for Express, Nginx, Apache, Next.js, and Cloudflare Workers.

CORS Policy Configuration

Select allowed origins, verbs, credentials, and preflight TTL.

Allowed Origin(s) (comma separated or *)

Allowed HTTP Methods

Allowed Request Headers

Max-Age Preflight (sec)

Exposed Headers

Allow Credentials (Cookies, Authorization tokens)

CORS Presets:

// Express.js with 'cors' middleware
const cors = require('cors');

const corsOptions = {
  origin: ["https://app.example.com","https://admin.example.com"],
  methods: ['GET', 'POST', 'PUT', 'DELETE', 'OPTIONS'],
  allowedHeaders: ['Content-Type', 'Authorization', 'X-Requested-With'],
  exposedHeaders: ['Content-Length', 'X-Total-Count'],
  credentials: true,
  maxAge: 86400
};

app.use(cors(corsOptions));

Mastering Cross-Origin Resource Sharing (CORS) Security

Cross-Origin Resource Sharing (CORS) is a browser security mechanism that uses HTTP headers to tell browsers whether web applications running at one origin have permission to access resources from a different origin. Misconfigured CORS headers can leave APIs vulnerable to data exfiltration via Cross-Site Scripting (XSS) or break legitimate single-page applications with preflight OPTIONS failures.

Key Technical Features

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Multi-Origin Whitelisting

Configure wildcard (*), specific domains, credential-safe origin lists, or regex patterns.

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Preflight OPTIONS Engine

Generates Access-Control-Max-Age caching headers to reduce latency from repeated OPTIONS preflights.

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Multi-Platform Configuration Exporter

Instantly export copy-paste rules for Express.js, Nginx, Apache .htaccess, Next.js next.config.js, and Cloudflare Workers.

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Credentials & Cookie Protection

Ensures proper Access-Control-Allow-Credentials pairing with non-wildcard origins to avoid browser security rejections.

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Granular Methods & Headers Filtering

Allow or restrict standard verbs (GET, POST, PUT, DELETE, PATCH, OPTIONS) and custom headers.

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One-Click Snippet Copy

Copy clean, syntactically verified server config snippets directly into your deployment pipeline.

Engineering & DevOps Scenarios

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Full-Stack Web Developers
Resolve 'No Access-Control-Allow-Origin header present' browser errors during API integrations.
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DevOps & Cloud Engineers
Standardize Nginx reverse proxy and API Gateway CORS policies across staging and production.
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Next.js & Frontend Engineers
Configure rewrites and custom headers in next.config.js for micro-frontend architectures.
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Security Engineers & Auditors
Verify that sensitive APIs do not inadvertently expose credentials alongside wildcard origins.

Frequently Asked Questions

Why do browsers block CORS requests?

Browsers enforce the Same-Origin Policy (SOP) by default to prevent malicious scripts on one website from reading confidential data from another website without explicit server consent via CORS headers.

Can I use 'Access-Control-Allow-Origin: *' with credentials?

No. Modern web browsers strictly reject requests where Access-Control-Allow-Credentials is set to 'true' if Access-Control-Allow-Origin is set to wildcard '*'. You must return the specific requesting origin in the header instead.

What is a CORS preflight request?

A preflight request is an automatic HTTP OPTIONS request sent by the browser before the actual request to verify that the server permits the HTTP method and custom headers of the upcoming cross-origin request.

What does Access-Control-Max-Age do?

It specifies the duration (in seconds) that the browser can cache the result of a preflight OPTIONS request. Caching preflights (e.g., 86400 seconds / 24 hours) dramatically improves API response speed by eliminating redundant round-trips.