HTTP Status Codes

503 Service Unavailable

The server is temporarily down — overloaded or in maintenance — but expected back. A Retry-After header tells clients and crawlers when to return.

What it means

503 Service Unavailable is a temporary condition: the server is overloaded or intentionally offline for maintenance. It should carry a Retry-After header. For planned maintenance, 503 is the SEO-safe status — search engines hold the URL rather than deindexing it.

HTTP RESPONSE
HTTP/1.1 503 Service Unavailable
Retry-After: 120
Content-Type: text/html

SEO impact

Use 503 for maintenance

During planned downtime return 503 with Retry-After, not a 200 maintenance page. Crawlers then pause and revisit instead of indexing an empty page or dropping the URL.

Why it matters

  • It protects rankings during maintenance and overload by signalling a temporary, retriable state.
  • Retry-After coordinates client and crawler backoff.

Common mistakes

  • Serving maintenance pages with 200, risking soft-404 indexing.
  • Omitting Retry-After, leaving clients to guess when to return.

How WebInspect checks this

  • WebInspect flags 5xx responses and reports Retry-After presence for maintenance/overload states.