When a page fails, the error screen always shows a number: 404, 502, 503… Not random — these codes are the shorthand language between browser and server. Read them and you instantly know whose problem it is.
Four Families, Four Responsibility Zones
- 2xx success: request handled fine — 200 is the everyday case.
- 3xx redirect: the resource moved. 301 (permanent) and 302 (temporary) mean different things to search engines.
- 4xx client error: your side — wrong URL, missing permission, or too many requests.
- 5xx server error: the website's side; usually all you can do is wait.
The 7 Codes You'll Actually See
| Code | Meaning | Cause & Fix |
|---|---|---|
| 200 | OK | All good |
| 301/302 | Redirect | Permanent / temporary; different SEO weight |
| 403 | Forbidden | No permission or IP blocked; check login |
| 404 | Not found | Typo or page deleted; check the URL |
| 500 | Server error | Their code broke; wait for the fix |
| 502 | Bad gateway | Backend down; retry in a few minutes |
| 503 | Unavailable | Overloaded or in maintenance; try later |
Three Self-Checks Before Blaming Anyone
- Try another site or switch to mobile data — rules out local network and DNS
- Re-read the full URL for typos (wrong query params also produce 4xx on APIs)
- Check your own browser fingerprint — some 403s are risk-control false positives
Recommended Tools
My Browser Info
See your User-Agent, screen, CPU cores, timezone and other browser details.
HTTP Status Codes
A searchable reference of HTTP status codes and what they mean.
URL Parser
Break any URL into protocol, host, path and query parameters.
Free online, images never leave your browser
FAQ
Do 404s hurt SEO?
A few are normal; masses of them waste crawl budget and drag down experience scores. Webmasters should 301 deleted pages to related content or serve a proper 404 page.
Is 502 my computer's fault?
No. 502 means the remote backend didn't answer — server-side by definition. Retry later; if it persists for hours, the site is having an outage.