Browser CORS Error — Access-Control-Allow-Origin Fix

Fix CORS (Cross-Origin Resource Sharing) errors in the browser. The server needs to allow cross-origin requests. 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: Error: Access to fetch has been blocked by CORS policy. Browser: All browsers. Category: Security/API Error. Cross-origin request blocked by browser. Understanding these fundamentals will help you diagnose and resolve this issue more effectively.

The most common reasons this occurs include: Server missing Access-Control-Allow-Origin header. Preflight OPTIONS request failed. Credentials included but server does not allow. Different protocol, domain, or port triggers CORS. Identifying the root cause is the first step toward finding the right solution.

To resolve this, follow these recommended steps: Server: add header Access-Control-Allow-Origin: * (or specific origin). For credentials: set Access-Control-Allow-Credentials: true. Handle OPTIONS preflight: respond with correct CORS headers. Development: use a CORS proxy or browser extension temporarily. Ensure API and frontend are on the same domain in production. 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.