Quiz Entry - updated: 2026.07.14
What do the HTTP status code categories (1xx-5xx) mean?
The first digit is the headline: 1 info, 2 success, 3 redirect, 4 you (the client) messed up, 5 the server messed up.
Every HTTP response carries a three-digit status code, and the leading digit alone tells you how things went. Learning the five families first lets you guess the meaning of any code you have never seen.
| Class | Category | Meaning |
|---|---|---|
| 1xx | Informational | request received, still processing |
| 2xx | Success | request received, understood, and accepted |
| 3xx | Redirection | more action needed, e.g. a redirect |
| 4xx | Client error | the request is invalid or not allowed |
| 5xx | Server error | server failed to fulfil a valid request |
The ones worth memorizing:
| Code | Name | Meaning |
|---|---|---|
| 200 | OK | success |
| 201 | Created | a new resource was created |
| 301 | Moved Permanently | resource has a new permanent URL |
| 302 | Found | temporary redirect |
| 400 | Bad Request | malformed syntax |
| 401 | Unauthorized | you must authenticate first |
| 403 | Forbidden | authenticated, but not allowed |
| 404 | Not Found | no such resource |
| 500 | Internal Server Error | generic server-side failure |
| 503 | Service Unavailable | server overloaded or under maintenance |
Gotcha: 401 vs 403 trips people up — 401 means "I don't know who you are, log in", while 403 means "I know who you are, and you still can't have this".
Go deeper:
HTTP response status codes (MDN) — the full, searchable reference for every code, organized by class.- List of HTTP status codes (Wikipedia) — conceptual overview plus the non-standard codes you meet behind Cloudflare/nginx.
- Redirections in HTTP (MDN) — how the 3xx class actually works via the
Locationheader (301 vs 302 vs 307/308).