Cross-Origin Resource Sharing (CORS) is an essential mechanism in web development, but it can be a nightmare for devs dealing with APIs. In this guide, we simplify what CORS is, how it works, and how to fix common errors.

What is CORS, Really?

CORS is a browser security feature that blocks requests from one domain to another unless the target domain explicitly allows it. For example, your frontend hosted at glesyde.solutions can't call an API from another domain without proper headers.

CORS Fix Checklist

• 🛠️ Set correct headers: Access-Control-Allow-Origin
• 🔁 Handle preflight (OPTIONS) requests
• ⚙️ Use proxy configs during local development
• 🔒 Don't allow wildcard origins in production
• 🌍 Test with Postman or browser DevTools

Common CORS Errors and Fixes

• **Blocked by CORS policy** – Missing Access-Control-Allow-Origin header • **Preflight issues** – Misconfigured OPTIONS method on the backend • **Credentials error** – Cookies not allowed without withCredentials flag + CORS headers Fixing CORS starts with your server.

CORS in a Multi-Domain App

Running a headless CMS, CDN, and frontend separately? CORS must be planned early in development. Using reverse proxies (like NGINX) or middleware (in Django, Node.js) can simplify your flow.