The HTTP status code 503 Service Unavailable means the server is not ready to handle the request. It describes a temporary condition, for example maintenance or overload.
At a glance
- Status code
- 503
- Class
- 5xx (server error)
- Duration
- temporary
- In Google
- crawling slows down; named by Google for short shutdowns (1-2 days)
- Retry-After
- optional, seconds or date (RFC 9110, section 10.2.3)
- Specification
- RFC 9110, section 15.6.4
Last checked:
When is 503 the right code?
MDN lists server maintenance, overload (memory, CPU or connection limits) and automatic rejection during software updates as common causes. The response should include a Retry-After header with the expected recovery time, either in seconds or as an HTTP date. 503 responses should not be cached, because clients could keep seeing the error page after the fix.
MDN separates 503 from 429. 503 covers temporary server problems, 429 covers rate limiting for a specific client.
What does 503 mean for SEO?
Google lists 503 among the 5xx errors that make its crawlers slow down temporarily and lower the crawl rate. URLs that persistently return a server error are removed from the index, and Google gives no time frame. A 503 for a short planned break therefore signals that the page will return, while a long-lasting 503 puts indexed URLs at risk.
With 503 or 429, a Retry-After header can be added. According to Google’s documentation on reducing the crawl rate, it tells crawlers when they can retry, as a delay in seconds or an absolute UTC date and time. Google advises against using these codes for longer than one to two days, and a URL may be dropped from the index if Googlebot sees them on it for multiple days. Google’s current guidance on temporarily disabling a site names a 503 response for urgent downtime of one to two days.
| Status code | Meaning per RFC | How Googlebot reacts | Effect on the index | Retry-After |
|---|---|---|---|---|
| 429 Too Many Requests | too many requests in a given amount of time (rate limiting, RFC 6585) | treated as a sign of an overloaded server and as a server error; crawling temporarily slows down | indexed URLs are kept for now; if Googlebot sees the code on the same URL for multiple days, it may be dropped | RFC: may be included; Google: tells crawlers when they can retry |
| 500 Internal Server Error | unexpected condition on the server | the site's crawl rate drops in proportion to the number of URLs returning a server error | indexed URLs are kept for now; persistent errors get them removed, possibly after multiple days on the same URL | Google only describes it for 503 and 429 |
| 502 Bad Gateway | a gateway or proxy got an invalid response from the server behind it | same as 500 | indexed URLs are kept for now and removed if the error persists | Google only describes it for 503 and 429 |
| 503 Service Unavailable (this term) | temporarily unavailable, for example due to overload or maintenance | same as 500 | indexed URLs are kept for now; if Googlebot sees the code on the same URL for multiple days, it may be dropped | RFC: may be included and states the expected downtime; Google: tells crawlers when they can retry (seconds or a date) |
| 504 Gateway Timeout | a gateway or proxy didn't get a timely response from the server behind it | not listed individually by Google; for all 5xx codes, crawling temporarily slows down | indexed URLs are kept for now but eventually dropped (statement for all 5xx) | Google only describes it for 503 and 429 |
Google ignores any content it receives with a 5xx response. Once the server responds with 2xx again, Google gradually increases the crawl rate. To deliberately reduce crawling for a short time (a few hours up to 1-2 days), Google names 500, 503 or 429 and advises against doing so for longer. Google treats network timeouts, connection resets and DNS errors similarly to 5xx errors; according to Google, unreachable URLs are removed from the index within days. Sources: Google Crawling Infrastructure: How HTTP status codes affect Google's crawlers (last updated 2026-02-04); Google Crawling Infrastructure: Reduce the Google crawl rate (last updated 2026-10-06); Google Crawling Infrastructure: Debug network and DNS errors (last updated 2025-12-18); RFC 9110: HTTP Semantics, 15.6 Server Error 5xx and 10.2.3 Retry-After; RFC 6585: Additional HTTP Status Codes, 4. 429 Too Many Requests. Last checked: .
Example
HTTP/1.1 503 Service Unavailable
Retry-After: 3600
Content-Type: text/html
<h1>Back soon</h1>
Common mistakes
- 503 for several days. Google advises against returning 503 for longer than one to two days. If Googlebot sees the code on the same URL for multiple days, the URL may be dropped from the index.
- Error page with status 200. A maintenance page returning 200 looks like normal content to crawlers. According to Google, Search Console reports a soft 404 error when the content suggests an error.
- robots.txt returning 503. If robots.txt returns a server error, Google stops crawling the site at first, according to its robots.txt specification.
Sources
- 503 Service Unavailable – MDN Web Docsdeveloper.mozilla.org
- Retry-After header – MDN Web Docsdeveloper.mozilla.org
- How HTTP status codes affect Google's crawlers – Google Crawling Infrastructuredevelopers.google.com
- RFC 9110: HTTP Semantics, section 15.6.4 (503 Service Unavailable) – IETFrfc-editor.org
- Temporarily pause or disable a website – Google Search Centraldevelopers.google.com
- Reduce the Google crawl rate – Google Crawling Infrastructuredevelopers.google.com
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