5xx Error
01 Definition
5xx Error meaning: A server-side HTTP status code showing the server failed to fulfill a valid request.
A 5xx error is any HTTP response in the 500 range, such as 500, 502, or 503, that signals a problem on the server rather than the request itself. Search engines that repeatedly hit these errors may slow crawling and, if the problem lasts, drop affected pages from the index.
Also called
Why it matters
How 5xx Error fits the work
Frequent 5xx errors tell search engines your pages are unreliable, which can reduce how often they crawl and whether your content stays indexed.
In context
During a traffic spike the site returned 503 errors on 40 percent of requests, so Googlebot backed off and crawl volume fell that day.
Practical note
Use a 503 with a Retry-After header for planned maintenance so crawlers know to return, rather than a generic 500 that looks like a lasting failure.