What causes a 500 Internal Server Error?

Something broke on the server side, a code bug, a crashed process, a database failure, or a misconfiguration. Check your server logs; the code itself won't tell you more.

Is 404 always a missing page?

Usually, but APIs also return 404 for missing resources (a deleted record, a wrong ID). It means the server couldn't find what was requested at that URL.

Does this reference work offline?

Yes, once the page loads, the entire reference is local. Search and browse work without a connection.

HTTP Status Codes

Look up every HTTP status code with plain-English meanings.

Search status codes

39 of 39 codes

About this tool

Every developer meets HTTP status codes daily, in browser dev tools, API responses, and server logs, but remembering what 418 or 502 actually means is nobody's idea of fun. This free reference covers 40+ status codes across all five classes, each with a plain-English explanation, typical causes, and practical fix guidance.

Search by code number or by keyword ("redirect", "auth", "timeout") and filter by class to narrow things down. Each entry explains not just what the code means but what to do about it, the difference between a 301 and 302 redirect, why a 429 means you need to slow down, and where to look when a 500 appears.

How to use the http status codes

1Type a code (e.g. 404) or keyword (e.g. "redirect") in the search box.
2Browse the category filters: 1xx informational, 2xx success, 3xx redirection, 4xx client errors, 5xx server errors.
3Click any code to expand its plain-English explanation, common causes, and fixes.
4Use it as a quick reference while debugging APIs and websites.

Good to know

The whole reference ships with the page, so search is instant and works offline. Keep it open in a tab while you debug, it's faster than searching the web every time a three-digit number shows up in your logs.

Frequently asked questions

301 is permanent, browsers and search engines update their bookmarks and indexes to the new URL. 302 is temporary, they keep the old URL. Use 301 for moved pages, 302 for short-term detours.

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