503 Service Unavailable | HTTP Status Code

Explanation

The 503 (Service Unavailable) status code indicates that the server is currently unable to handle the request due to a temporary overload or scheduled maintenance, which will likely be alleviated after some delay. The server MAY send a Retry-After header field to suggest an appropriate amount of time for the client to wait before retrying the request.

This status is commonly used during:
- Server maintenance windows
- High traffic periods exceeding the server's capacity
- Failure of a service component (like a database) needed to fulfill requests
- Rate limiting or throttling at the infrastructure level

A well-designed 503 response will inform the client about when they can retry the request, either through human-readable text or the Retry-After header which provides a delay in seconds or a specific date/time when to retry.

Example Response

HTTP/1.1 503 Service Unavailable
Retry-After: 120
Content-Type: text/html

<html>
<head>
<title>Service Unavailable</title>
</head>
<body>
<h1>Service Unavailable</h1>
<p>The server is temporarily unable to handle the request due to maintenance downtime. Please try again in a few minutes.</p>
</body>
</html>

Related Status Codes

500 500 Internal Server Error 502 502 Bad Gateway 504 504 Gateway Timeout