What are the 5 HTTP status code classes?

1xx informational, 2xx success, 3xx redirection, 4xx client error, and 5xx server error. The first digit defines the class.

What is the difference between 401 and 403?

401 Unauthorized means you are not authenticated (missing or invalid credentials). 403 Forbidden means you are authenticated but not allowed to access the resource.

404 Not Found means the server could not find the requested resource at that URL. The route or file does not exist.

When should I use 301 vs 302?

301 is a permanent redirect (update bookmarks and SEO), while 302 or 307 is temporary and keeps the original URL as canonical.

500 Internal Server Error is a generic server-side failure. The request was valid but the server could not complete it; check server logs.

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Reference

HTTP Status Codes

Complete reference for all HTTP response status codes.