The five classes
- 1xx (informational): the request was received and is being processed.
- 2xx (success): 200 OK means the page loaded normally.
- 3xx (redirection): the content is at another URL, as with 301 (moved permanently), 302 (found, temporary), 307 and 308, or 304 (not modified, use the cached copy).
- 4xx (client errors): the request can’t be fulfilled, such as 400 (bad request), 401 (unauthorized), 403 (forbidden), 404 (not found), 410 (gone) and 429 (too many requests).
- 5xx (server errors): the server failed, such as 500 (internal server error), 502 (bad gateway) and 503 (service unavailable).
Why status codes matter for SEO
- Only pages that return 200 can be indexed.
- 301 redirects send visitors and links on to the new URL.
- 404 and 410 pages drop out of the index over time.
- Frequent 5xx or 429 errors make Google crawl less; a short 503 is the right response during maintenance.
- “Soft 404s”, error pages that return 200, confuse search engines and waste crawl budget.
You can check status codes with your browser’s developer tools, a crawler such as Screaming Frog, or the Pages and Crawl Stats reports in Google Search Console.