HTTP status codes

How to use the HTTP Status Codes tool

1. Type a code (502) or a word (redirect, timeout).
2. Filter by class: 1xx to 5xx.
3. Read the meaning and typical causes.

The five classes

• 1xx Informational: the request is in progress.
• 2xx Success: the request worked.
• 3xx Redirection: the client must go somewhere else.
• 4xx Client error: the request is wrong, unauthorised or points to nothing.
• 5xx Server error: the request was fine but the server failed.

Debugging the errors you see most

• 403 Forbidden: file permissions or ownership, a missing index file with directory listing off, an IP restriction or a WAF rule. Check the web server error log, not just the access log.
• 404 Not Found on every page except the home page of a WordPress site: the rewrite rules are missing. Re-save permalinks or check the nginx try_files line.
• 500 Internal Server Error: an application crash. The answer is in the PHP, Python or Node log.
• 502 Bad Gateway: the proxy could not talk to the backend. Is PHP-FPM or the app container running? Does the socket path match?
• 504 Gateway Timeout: the backend is too slow. Look for a slow database query before raising timeouts.

For SEO: use 301 for permanent moves so search engines transfer rankings, 410 for content you removed on purpose, and never answer errors with 200 and an error page (a “soft 404”), which confuses search engines.

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Frequently asked questions