← Back to all status codes
5xx Series
Safe to retry
503 Service Unavailable
The server is currently unavailable (because it is overloaded or down for maintenance). Generally, this is a temporary state.
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SEO Impact
Crucial for maintenance. If you use a Retry-After header, Googlebot will pause and return later without deleting your SEO index.
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Common Causes
- 1Planned server maintenance
- 2Sudden massive traffic spike overloading CPU
- 3Database migrations in progress
Code Examples
PHP
header('HTTP/1.1 503 Service Temporarily Unavailable');
header('Retry-After: 3600');