503 Service Unavailable

What it means

Usually due to maintenance or overload. A Retry-After header can say when to try again.

Common causes

• Planned maintenance.
• Traffic overload or exhausted server resources.
• Auto-scaling that has not caught up.

How to fix it

1. Wait and retry.
2. Scale server capacity or add caching.
3. During maintenance, return 503 with Retry-After.

Example response

HTTP/1.1 503 Service Unavailable
Content-Type: text/plain; charset=utf-8

Worked example

A gateway or server cannot complete an otherwise valid request. Check the origin service and proxy logs, correct the server-side cause, then retry after the service is healthy.

How to read this response

1. Find the status line in your browser's Network panel, API client, or server access log.
2. Read the response body and headers shown above; headers such as Location, Allow, Retry-After, and WWW-Authenticate explain the next step.
3. Use the code's class to orient your diagnosis: informational, successful, redirected, request-related, or server-side.

SEO impact

503 with Retry-After is the correct response for planned maintenance; search engines retry instead of dropping pages.

How to check a status code

Enter a URL in the HTTP Status Checker to see its status code, every redirect hop, and response time. For redirect-heavy pages, the Website Speed Test shows how much time redirects add.

Frequently asked questions

What it means: HTTP 503

503 Service Unavailable: The server is temporarily unable to handle the request.

Common causes: 503

Planned maintenance. Traffic overload or exhausted server resources. Auto-scaling that has not caught up.

How to fix it: HTTP 503

Wait and retry. Scale server capacity or add caching. During maintenance, return 503 with Retry-After.

Tools