5xx errors
Also called: 5xx, server errors, 5xx server error, 500 error
A 5xx error is an HTTP status code in the 500-599 range that means the server failed to fulfill an otherwise valid request. Common ones are 500 (Internal Server Error), 502 (Bad Gateway), 503 (Service Unavailable), and 504 (Gateway Timeout). The fault is on the server, not the request.
How Google treats 5xx responses
When Googlebot hits a URL that returns a 5xx code, it ignores whatever content came back and temporarily slows its crawl rate. The slowdown scales with how many of your URLs are erroring, so a site-wide outage throttles crawling harder than one broken page. Already-indexed URLs stay in the index at first, but if Googlebot keeps seeing a 5xx on the same URL across multiple days, that URL may be dropped. Once your server returns 2xx responses again, Google gradually raises the crawl rate back up.
Not every 5xx is a defect. 503 Service Unavailable is the correct, deliberate response during planned maintenance or overload, and it should carry a Retry-After header so crawlers know when to return. Google even suggests returning 503 or 429 to throttle Googlebot when your server is straining, but only for a day or two, not as a standing state.
Typical causes: an origin crash (500), a reverse proxy or CDN getting a bad upstream reply (502), a database connection or PHP-FPM pool exhausted under load, or an upstream timeout (504). Intermittent 5xx usually points at resource limits rather than broken code, which is exactly why they are easy to miss. Tracing them to the origin and confirming 503s are used correctly for maintenance is standard Technical SEO triage.
How it affects your traffic
Sustained 5xx responses pull pages out of Google's index and cut how often Googlebot crawls the whole site, so rankings and new-content discovery both stall at once. Because the errors are often intermittent, they slip past manual QA and only surface in Search Console's Page Indexing report after traffic has already dropped. Catching those patterns in log and crawl data, fixing the origin, and using 503 correctly during maintenance so crawling recovers fast is core technical-SEO triage our Technical SEO service handles.
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