HTTP 503 — Service Unavailable
5xx Server Error
What it means
The server is temporarily unable to handle the request — overloaded, or down for maintenance.
What to do about it
Send a Retry-After header so clients and crawlers know when to come back. Google treats a short 503 as temporary and will not drop the page from its index.
Where it sits
503 belongs to the 5xx family: The server failed to fulfil an apparently valid request. The fix is on the server side.
HTTP/1.1 503 Service UnavailableChecking it yourself
# see the status code and headers only
curl -sI https://example.com/path
# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path
# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);