Status codes are grouped by first digit: 2xx means success, 3xx means redirect, 4xx means a client error such as a missing page, and 5xx means a server error.
The common ones in SEO are 200 (OK), 301 (moved permanently), 302 (found, temporary), 404 (not found), 410 (gone) and 503 (service unavailable).
Search engines use status codes to decide whether to index a page, follow a redirect or drop a URL. A wrong code, such as a 200 on an error page, sends the wrong signal.
VisibilityKit Crawler records the status code for every URL and groups issues by response. When you re-check a fix, it records what the site actually returned, and a timeout or 503 is reported as uncertain rather than counted as a pass.
404 or 410. Use a 301 redirect instead if there is a clear replacement page.
Temporarily unavailable. Search engines will retry later, but a 503 that lasts days can lead to pages being dropped.
The HTTP status a server returns when the requested page does not exist.
A page that looks like an error or empty page to users but returns a 200 OK status to crawlers.
A 301 redirect signals a permanent move; a 302 signals a temporary one.
A sequence of two or more redirects between the requested URL and the final destination.
Re-checking a page after a fix ships to confirm, with evidence, that the issue is actually resolved.
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