HTTP 503 Service Unavailable for maintenance
503 Service Unavailable means the server is temporarily unable to handle the request, usually due to maintenance or overload. It is the correct, index-protecting status for planned downtime: with a Retry-After header, compliant crawlers understand the outage is temporary and come back later.
What 503 means
503 Service Unavailable indicates the server is currently unable to handle the request due to temporary overload or scheduled maintenance, and that the condition is expected to be temporary. The response should include a Retry-After header where possible, indicating when the client can try again.
It is the standard way to say 'temporarily down, not broken'.
Why 503 protects your index
If your site goes down and requests fail with 500s — or worse, return a maintenance page with a 200 — crawlers can misread the situation: 500s look unhealthy, and a 200 maintenance page risks indexing the wrong content. A 503 with Retry-After tells compliant crawlers the outage is temporary, so they back off and return rather than de-indexing pages.
Use 503 for the whole maintenance window, including the maintenance page itself, and remove it as soon as you are back.
- 503 + Retry-After signals a temporary outage
- Do not serve a maintenance page with a 200 status
- Do not use 500 for planned downtime
Operator checklist
For maintenance or overload, return 503 with a Retry-After header for all affected requests, including the maintenance page. Keep the window short and remove the 503 immediately afterwards. Confirm pages return to 200 once you are live again.
How it appears in analytics and logs
A 503 means the server is temporarily unavailable. For crawlers, paired with Retry-After, it signals 'come back later' rather than 'this page is broken', so they slow down and retry instead of dropping the URL.
Diagnostic use case
Serve planned maintenance or overload responses in a way crawlers understand as temporary, protecting your index from being treated as broken.
What WebmasterID can help detect
WebmasterID can show whether crawlers receive 503s during maintenance windows, helping you confirm downtime is being signalled correctly rather than as hard errors.
Common mistakes
- Serving a maintenance page with a 200 status instead of 503.
- Using 500 for planned downtime, making the site look broken.
- Returning 503 without a Retry-After header.
Privacy and accuracy notes
Status codes carry no personal data. WebmasterID reports 503 patterns for crawler traffic without exposing individual visitors.
Related pages
- HTTP 500 and crawl health
500 Internal Server Error is a generic message that something went wrong on the server and it could not complete the request. Occasional 500s happen, but repeated 500s on important URLs harm crawl health: crawlers may slow down and, if errors persist, treat affected pages as unreliable.
- HTTP 429 Too Many Requests and crawl rate
429 Too Many Requests means the client has sent too many requests in a given time and is being rate limited. It can include a Retry-After header telling the client when to try again. Compliant crawlers slow down in response, making 429 a controlled way to manage crawl rate.
- Website observability
Confirm maintenance windows return 503, not hard errors.
Sources and verification notes
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.