503 Service Unavailable.

A 503 Service Unavailable response tells the client that the server is temporarily unable to handle the request—typically due to maintenance, traffic overload, or a downstream dependency failure. It is a server-side (5xx) error indicating the problem is with the server, not the client's request.

SEO Implications of 503 Errors

Brief, occasional 503 errors have minimal SEO impact—Googlebot retries URLs that return 503s and typically does not immediately de-index them. However, sustained 503 responses across many URLs signal server instability to Google. If Googlebot repeatedly encounters 503s over days, it reduces crawl frequency, which can delay indexing of new or updated content.

Using 503 for Planned Maintenance

When taking a site offline for planned maintenance, returning a 503 (along with a `Retry-After` header specifying when the site will be back) is the correct approach. This signals to Googlebot that the downtime is temporary and that it should return later rather than treating all affected URLs as permanently unavailable. Never return a 200 OK with a maintenance page—that creates site-wide soft 404s.