What it means
503 is a temporary error: the server is running but isn't accepting requests at the moment. The response can include a Retry-After header saying when to try again. It's the correct code for planned maintenance.
Most common causes
- Overload from traffic or an attack.
- Planned maintenance or an update (e.g. WordPress “Briefly unavailable for scheduled maintenance”).
- Exhausted worker processes (PHP-FPM, application server).
- A backend service or database is unavailable.
- Hosting limits (resources used up).
What you can do as a visitor
- Wait a few minutes and try again.
- Check whether the site is down for others too.
- For popular services, check their status page.
What the site owner or developer should do
- For maintenance, return 503 with Retry-After, not 200 or 404.
- Check server load, process counts and logs.
- WordPress: if a .maintenance file is left behind after an update, delete it.
- Use a CDN and caching to handle traffic spikes.
Impact on SEO and Google
Google understands a 503 as a temporary state and comes back later. Short maintenance with a 503 is safe; a 503 lasting several days can lead to URLs being dropped from the index.
Frequently asked questions
Does a 503 mean the site is shut down?
No. It means it's temporarily unavailable.
How long is a 503 safe for SEO?
A few hours, up to a day or two at most. Any longer can affect indexing.