HTTP 503 Service Unavailable — Meaning, Causes & How to Fix
The server is not ready to handle the request, usually due to overload or maintenance.
- Code
- 503
- Name
- Service Unavailable
- Class
- 5xx Server Error
- Specification
- RFC 9110 §15.6.4
- Cacheable by default
- Only with explicit Cache-Control / Expires
What HTTP 503 means
503 Service Unavailable means the server temporarily cannot handle the request — because of maintenance or overload — and expects to recover. It may send Retry-After to say when to try again. It is the correct code for planned downtime.
Common causes
- A maintenance mode page.
- Server overload or exhausted worker processes.
- An application that is starting up or a dependency that is down.
- Hosting resource limits being hit.
How to fix it
For site owners
- For maintenance, return 503 with
Retry-After— not a 200 maintenance page. - Keep downtime short; scale or cache if the cause is load.
For visitors & developers
- Wait and retry; respect
Retry-Afterif present.
SEO impact
The SEO-safe way to go offline. Googlebot treats 503 as temporary, slows its crawl and retries later instead of dropping pages. If 503s persist for more than a couple of days, Google may start removing URLs, so keep it short.
Example 503 response
HTTP/1.1 503 Service Unavailable
Retry-After: 3600
Content-Type: text/html; charset=utf-8
Cache-Control: no-storeRelated status codes
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Open HTTP Status Codes tool →All status codesFrequently asked questions
What does HTTP 503 mean?
HTTP 503 Service Unavailable is a 5xx Server Error status code. The server is not ready to handle the request, usually due to overload or maintenance.
Should I use 503 for site maintenance?
Yes. 503 with a Retry-After header tells search engines the downtime is temporary. A 200 maintenance page could get indexed in place of your real content.
How long can a site return 503 without SEO damage?
Short periods (hours) are fine. Google has said that if 503s continue for more than a couple of days, URLs may start to drop out of the index.
Which specification defines 503?
It is defined in RFC 9110 §15.6.4.
Is a 503 response cacheable?
Not by default. A 503 response is only stored by caches when it carries explicit freshness information such as Cache-Control: max-age or Expires.