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

Criticalbrowser general

Overview

Fix CORS (Cross-Origin Resource Sharing) errors in the browser. The server needs to allow cross-origin requests.

Key Details

  • Error: Access to fetch has been blocked by CORS policy
  • Browser: All browsers
  • Category: Security/API Error
  • Cross-origin request blocked by browser

Common Causes

  • 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

Steps

  1. 1Server: add header Access-Control-Allow-Origin: * (or specific origin)
  2. 2For credentials: set Access-Control-Allow-Credentials: true
  3. 3Handle OPTIONS preflight: respond with correct CORS headers
  4. 4Development: use a CORS proxy or browser extension temporarily
  5. 5Ensure API and frontend are on the same domain in production

Tags

browserbrowser-generalbrowser cors errorwebfix

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Frequently Asked Questions

A browser security policy that blocks requests to a different origin (domain:port).