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5xx Server Error
What it means
The server is temporarily unable to handle the request, usually due to maintenance or overload.
| Property | Detail |
|---|---|
| Status class | 5xx Server Error |
| Defined in | RFC 9110, Section 15.6.4 |
| Cacheable by default | Only with explicit caching headers: a cache stores it when the response carries Cache-Control (max-age, s-maxage or public) or Expires. |
| Who needs to act | The site owner. Visitors can only wait. |
What does HTTP 503 Service Unavailable mean?
HTTP 503 Service Unavailable means the server is temporarily unable to handle the request, usually because of overload or scheduled maintenance, and expects to recover after some delay. It may send a Retry-After header saying when to try again. It is the correct status for planned downtime, because it tells clients and crawlers the outage is temporary.
How 503 Service Unavailable works
A 503 is the 5xx code that explicitly describes a temporary condition. When it comes with Retry-After, that header states how long the service is expected to be unavailable, either in seconds or as an HTTP date. Servers return it deliberately during maintenance, and infrastructure returns it automatically when no healthy backend is available or a queue is full. RFC 9110 adds a caveat: servers are not obliged to send 503 when overloaded and may simply refuse connections, so the absence of a 503 does not prove that a service is healthy.
Example 503 request and response
GET / HTTP/1.1
Host: example.com
HTTP/1.1 503 Service Unavailable
Retry-After: 3600
Content-Type: text/htmlRetry-After: 3600 tells browsers, API clients and crawlers that the site expects to be back within an hour.
What causes a 503 Service Unavailable
- Planned maintenance or a deploy behind a maintenance page.
- Traffic spikes beyond capacity, or exhausted connection and worker pools.
- A load balancer with no healthy backends, for example after failed health checks.
- WordPress showing 'Briefly unavailable for scheduled maintenance' during updates, or after an interrupted update left a .maintenance file behind.
How to fix a 503 Service Unavailable
If you are a visitor
- Wait and retry later, and check the site's status page or social accounts for maintenance notices.
If you run the site
- For planned maintenance, return 503 with Retry-After and a lightweight static page.
- Keep robots.txt returning 200 during maintenance, so crawling of the site is not blocked entirely.
- For overload, add capacity, enable caching, or shed load on non-critical routes.
- If WordPress is stuck in maintenance mode, delete the leftover .maintenance file in the site root.
- If no maintenance is planned, check load balancer health checks and backend status.
503 and SEO
A 503 is the right way to take a site offline briefly. Google slows crawling when it sees 503s, keeps indexed pages for the time being, and speeds up again when the site returns. Its guidance is to use 503 for outages of a day or two; if URLs keep returning 503 for several days, they may be dropped from the index. Never serve 503 for robots.txt, which blocks crawling of the whole site.
Related status codes
- 502 Bad Gateway: A proxy got a broken response from upstream: an unplanned failure.
- 504 Gateway Timeout: The upstream server was too slow to answer.
- 429 Too Many Requests: Only this client is being throttled, not the whole service.
- 500 Internal Server Error: An unexpected error, with no promise that it is temporary.
Frequently asked questions
The server is temporarily unable to handle the request, usually due to maintenance or overload.
Scheduled maintenance, a traffic spike overwhelming server capacity, or a dependency (like a database) being unavailable.
Wait and retry - check the response's Retry-After header if present, or the site's status page for planned maintenance.
Google's guidance is a day or two. Short maintenance windows served as 503 with Retry-After are safe, but if the same URLs keep returning 503 for several days, Google may start dropping them from its index.
Sources
- RFC 9110, Section 15.6.4
- RFC 9110, Section 10.2.3 (Retry-After)
- Google Search Central: Temporarily pause or disable a website
- Google: Reduce the Google crawl rate
- Google: How HTTP status codes affect Google's crawlers
Other 5xx Server Error codes
Reviewed by Raja Jahangir · Last reviewed: October 7, 2026