Why do I see a “503 Service Unavailable” error?

If you see a “503 Service Unavailable” error message on your Web site, it means that the site has reached the limit on how many simultaneous “requests” it can handle from you.

There are two important things to keep in mind about 503 errors:

We sometimes hear reports of 503 errors because a WordPress site owner starts running a server script that takes a long time, then opens a new browser tab and starts trying to do other things while the first thing is still going. But there’s a limit to how many things each connected IP address can do at once on a site — and that limit is useful, because it prevents the site owner (or anyone else) from using up so many script “slots” that other visitors can’t run scripts themselves.

If you see a 503 error on your own site and you’re wondering what’s wrong, don’t focus on the last thing you clicked on. Think back to what other things you tried doing on your site in the last few minutes that may not have finished yet. Those are the cause of the problem.

When you’ve identified what the cause is, you can either try to fix your script (if it shouldn’t be that slow), or just let it finish before you try doing other things (if it’s reasonable for it to be that slow).

In either case, other people probably aren’t seeing the same thing — your site’s probably not totally “down” — and it will almost certainly clear up if you leave things alone for a few minutes (because the already-running scripts will finish).

How can I tell if it’s just me?

We mentioned above that it’s probably only your computer being affected by this, but in rare cases, there can be a more general problem with your site or the server it’s on.

You can tell the difference by using a third-party test like CheckSite.us or Is My Blog Working?, which try to load your site from different computers. If these say things are working, but your own attempts to access it from your computer show 503 error messages, it’s just you. Waiting a few minutes will give you a fresh start.

What are some common causes of 503 errors on WordPress sites?

As a tip, here are a some of the causes of 503 errors we see repeatedly with WordPress: