HTTP Status Codes: The Ones You'll Actually See
404, 500, 301, 403 — web status codes are the server telling you what happened. Here's what each family means and the specific codes worth knowing.
Every time you load a page, the server sends back a three-digit status code — its one-line summary of what happened. You usually never see it, until something breaks. Learn the families and the codes stop being mysterious error noise.
The trick: the first digit tells you everything
Status codes are grouped by their first digit, and that grouping is the whole mental model:
- 2xx — Success. It worked.
- 3xx — Redirection. "It's somewhere else now."
- 4xx — Client error. "You (the request) did something wrong."
- 5xx — Server error. "I (the server) messed up."
That alone lets you triage any code: 4xx points at the request, 5xx points at the server.
The ones worth knowing by name
| Code | Means | In plain words |
|---|---|---|
| 200 | OK | All good, here's your page. |
| 301 | Moved Permanently | This page now lives at a new URL — for good. |
| 302 | Found (temporary) | Over here for now, but not permanently. |
| 304 | Not Modified | Nothing changed; use your cached copy. |
| 403 | Forbidden | You're not allowed here. |
| 404 | Not Found | No such page. |
| 429 | Too Many Requests | Slow down, you're being rate-limited. |
| 500 | Internal Server Error | The server crashed on this request. |
| 502 / 503 | Bad Gateway / Unavailable | The server's down or overloaded right now. |
4xx is the request's fault; 5xx is the server's fault. Half of all web debugging starts with that one distinction.
Why they matter beyond errors
Status codes drive real behaviour. A 301 tells search engines to move a page's ranking to the new URL — essential when you restructure a site. A 304 powers caching and makes return visits fast. A 429 is how APIs protect themselves. They're not just error pages; they're the web's control signals, exchanged on every request.
Key takeaways
- First digit tells the story: 2 success, 3 redirect, 4 your fault, 5 server fault.
- Know 200, 301/302, 304, 403, 404, 429, 500, 502/503.
- 301 redirects preserve SEO when a page moves permanently.
- 304 enables caching; 429 means you're being rate-limited.
Frequently asked questions
What's the difference between a 301 and a 302 redirect?
301 means 'moved permanently' — browsers and search engines update to the new URL. 302 means 'temporarily here.' For SEO, use 301 when a page has genuinely moved for good.
Is a 404 bad for SEO?
A few are normal and fine. Problems arise when important pages 404, or when broken links pile up. Redirect moved pages with a 301 and keep a helpful custom 404 page.