CORS: Why Does My API Work in Postman but Not in My Browser?

CORS: Why Does My API Work in Postman but Not in My Browser? You build your backend. You test the API in Postman. Everything works perfectly. Then you connect your React frontend… And suddenly: CORS error. What happened? Your API isn’t necessarily broken. CORS stands for Cross-Origin Resource Sharing. Browsers have security rules that control which websites are allowed to make requests to your server. For example: Your frontend: https://myapp.com Your API: https://api.myapp.com The browser sees that they’re different origins and checks whether the API allows the request. Your backend can respond with headers such as: Access-Control-Allow-Origin Basically telling the browser: “Yes, this website is allowed to access my API.” This is why something can work in Postman but fail in your browser. Postman isn’t enforcing the same browser-origin security rules. So when you see a CORS error, don’t immediately start changing random frontend code. Check: Is the backend allowing your frontend’s origin? Is the HTTP method allowed? Are the required headers allowed? Is your backend CORS configuration correct? Once you understand what CORS is actually protecting, the error becomes much less scary. Have you ever spent hours fighting a CORS error?