503 error
Also called: 503, service unavailable, http 503, 503 service unavailable error
A 503 error (HTTP 503 Service Unavailable) is a server status code telling the client the server cannot handle the request right now, usually because it is overloaded or down for maintenance. It signals a temporary condition, so crawlers should retry rather than treat the page as gone.
When your server is briefly down (maintenance, a traffic spike, a failing origin), returning 503 tells Googlebot the outage is temporary. Google’s crawlers read 5xx and 429 responses as a “slow down” signal: they back off the crawl rate and ignore any content the URL returns. Already-indexed URLs stay in the index for a while, but if the 503 keeps coming back long enough, those pages are eventually dropped. That is the opposite of a 404 (“gone, remove it”) or a 200 served with an error page (which risks a blank or thin page getting indexed).
Serve it correctly
Set a Retry-After header when you can. Per the HTTP spec it carries the estimated recovery time, as seconds or an HTTP date:
HTTP/1.1 503 Service Unavailable
Retry-After: 3600Do not cache 503 responses, or clients may keep seeing the error after you have fixed it. Common triggers are exhausted memory, CPU, or connection-pool limits, an overwhelmed worker or PHP-FPM pool, a plugin or CDN misconfiguration, or an aggressive rate limiter (a pure rate-limit case is better served as 429). The fix is usually capacity, caching, or config, not anything on the page itself. Keep planned maintenance windows short and predictable so no important URL sits behind a 503 for days.
How it affects your traffic
A stray or long-running 503 quietly bleeds rankings: Googlebot slows its crawl, stops picking up new content, and after a sustained outage starts dropping pages from the index, which is slow to win back. Intermittent 503s during traffic peaks also make your best pages unreachable exactly when demand is highest. A technical SEO audit catches this early. It checks response codes site-wide, spots pages flapping to 503 under load, confirms maintenance responses use 503 with Retry-After (not 200 or 404), and fixes the capacity or config root cause. That is the work our Technical SEO service handles.
Get Technical SEO that moves the needle
We turn terms like this into ranked pages and qualified pipeline. Start with a free Initial SEO Strategy.