Browser CORS Error

Browser CORS (Cross-Origin Resource Sharing) error means a web page tried to access a resource from a different domain that has not allowed it. This guide covers everything you need to know about this topic, including common causes, step-by-step solutions, and answers to frequently asked questions.

Here are the key things to understand: Access to fetch at URL has been blocked by CORS policy. Security feature preventing unauthorized cross-origin requests. Only affects browser requests, not server-to-server. Server must include Access-Control-Allow-Origin header. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: API server missing CORS headers. Wrong origin in Access-Control-Allow-Origin. Preflight OPTIONS request failing. Credentials included without proper CORS configuration. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: For developers: add Access-Control-Allow-Origin header on the API server. Use a CORS proxy for development testing. Check browser console for the specific CORS error. Verify OPTIONS preflight request is handled correctly. If these steps do not resolve the issue, consider consulting additional resources or a qualified professional.

This article is part of our Browser Errors collection on Error Codes Wiki. We provide comprehensive, up-to-date information to help you find solutions quickly.