5xx Server Errors
5xx status codes (500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout) indicate the server failed to fulfil a valid request.
In context
Persistent 5xx errors damage SEO in two ways: search engines de-prioritise crawling URLs that consistently return errors, and live users abandon. 503 is the only 5xx that signals 'temporary' to crawlers — use it (with a Retry-After header) during planned maintenance windows so Google does not de-index pages. 500/502/504 should be treated as production incidents, surfaced in monitoring, and resolved within minutes. Track 5xx rate per URL in log-file analysis.
A Canadian retailer's checkout endpoint started returning 502 for 3% of requests during a CDN config change — Search Console flagged it within 48 hours and the team rolled back.
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