About 5xx response status code

Published: Artem Prysyazhnuk 2024-03-04 all articles | Glossary | FAQ

Whenever you’re getting a message with the numerical code in it instead of the website, no matter how it’s designed, there’s almost a certainty that you’ve met an HTTP status notification. It literally tells you that something’s gone wrong. Usually, such notifiers appear when there’s a mishap in the web resource configuration, server malfunction, connection failure or user’s incorrect action (client request). And every notifier response has its own meaning, separated by the first digit in the number.

As an example, 1xx codes, usually unseen by users, are about continuation of the process that was prolonged or delayed for some reason. In turn, the 2xx set is about successful operation completion, and therefore such codes are also usually unseen. On the other hand, 3xx and 4xx groups are referring to redirection wrong configuration or user-made mistakes respectively. And the 500 status code set is about various server and network problems.

All code groups mentioned above are meant to notify users and webmasters about various issues happening whenever there’s a request to the webpage or the site. And while they have informational meaning and their contents are scarce, they literally point out errors, making the first step on the road to resolving them quickly on either side. And the 5xx codeset is one of the first instruments to help webmasters with server maintenance and its stability improvement.

5xx Status Codes In A Nutshell

5xx Status Codes In A Nutshell

Usually, whenever you see one of the notifiers from the 5xx codeset, you also see a short clarification. And in most cases those explanations in redirects to notifiers are hardly understandable for users who’re not tech-savvy and are not knowledgeable about how websites work. In general terms, 5xx codes are all notifiers about troublesome situations with the server or its network connectivity. And they literally mean that there’s a malfunction, the URL is inaccessible for some reason and it won’t be available for access until everything is fixed.

Take, for instance, status code 503, that states ‘Service Unavailable’ as its explanation. It’s a code that describes instances whenever the server is on maintenance and not reachable for anyone, or it’s overloaded and down. It could be a result of a variety of circumstances, including processing malfunctions, connectivity instabilities, software or hardware malfunctions and so on.

Therefore, as a user, if you see a redirect to such a message, then all you can do is wait. From the SEO perspective, such a notifier means that the resource won’t be recognized as an accessible one. And from the point of view of the webmaster, it means that the server is unavailable due to problems that must be fixed quickly.

Common 5xx Status Codes and Their Meanings

Common 5xx Status Codes and Their Meanings

No matter whether you’re a user, a SEO specialist or a webmaster, if you want to comprehend what meanings are behind the 5xx codeset messages, you need to be knowledgeable about them. Thankfully, those informational notifiers are systematic and their definitions were designated by the IETF service.

  • 500 - Internal Server Error. The designated status code 500 pops up whenever the server is actually normally functioning, but can’t resolve the instance properly or can’t appropriately respond in a way it should. All things considered, both users and search engine parsers will count the site with such a notifier showing up as inaccessible, so the matter must be fixed in the shortest time period possible.

  • 501 - Not Implemented. The notifier with the 501 status code is emerging in occurrences whenever the queried function is completely unsupported by the server. It incorporates various compatibility issues from mismatches between the user-side cached settings and the real ones up to server misconfiguration.

  • 502 - Bad Gateway. As literally one of the most commonly occurring notifiers, the 502 status code is displayed whenever there are complications with the connectivity on the server entry. Basically, it informs everyone that the gateway is unresponsive to queries or has received an inappropriate one, thus it’s impossible to let it through and proceed.

  • 503 - Service Unavailable. The notifier with the 503 status code shows up whenever the server is not ready for handling queries due to some circumstances. Usually it shows up in instances of currently ongoing maintenance or either hardware or software overloading. And it declares unresponsiveness or complete unavailability.

  • 504 - Gateway Timeout. The notifier incorporating the 504 status code is showing up in cases whenever receiving a query by the server takes too much time and is rejected by the gateway, therefore it can’t be appropriately handled.

  • 505 - HTTP Version Not Supported. The 505 status code is a rather complicated notifier. It clarifies that the server utilizes the HTTP revision that’s not identical to the one that’s used in the query, making fetching and handling the latter impossible. Usually it refers to circumstances when there’s a server misconfiguration, its software was not updated or the cached variant is outdated.

There is also the uncommon error notifier subgroup that carries warnings that are emerging only in instances whenever the server is working through the proxy by CloudFlare platform. Those were also clarified by the IETF to be specifically utilized with platform-related issues only.

  • 520 - Web Server Is Returning An Unknown Error. The notifier with the 520 status code is displayed whenever there’s something wrong with the server answer and it can’t be handled by the platform’s systems. There are several instances for it, depending on the circumstances, and they could originate from both sides.

  • 521 - Web Server Is Down. The notifier incorporating the web server is down error code 521 is emerging whenever the server cuts the connection to the platform’s proxy. Usually, such things happen whenever the platform was blacklisted due to misunderstanding queries from the proxy for DDoS attempts.

  • 522 - Connection Timed Out. The notifier with the 522 status code pops up whenever the server answer needs too much time and can’t reach the platform’s services. It can emerge due to a variety of causes, beginning with the initial misconfiguration and up to the misconfigured or messed up networking route.

  • 524 - A Timeout Occurred. The notifier incorporating the 524 status code is shown in cases whenever the platform’s systems have fetched the query but it’ll take more time than expected to handle it, therefore the return will be delayed for up to 100 seconds.

  • 530 - Site Frozen. The notifier with the 530 status code is rather strange and misleading. If properly set up, it will be displayed with the platform-specific 1xxx codeset addition. The latter usually has a more detailed clarification for what caused the issue.

On top of the notifiers that were mentioned above, there are also notifiers that are not only uncommon, but also non-existent, at least as far as IETF is concerned. For instance, there’s a status code 580 that is defined by a web app developer or webmaster. Obviously, its explanation and initial cause will be different in different cases.

Why Do 5xx Status Codes Appear?

Why Do 5xx Status Codes Appear

As it was mentioned above, 5xx codeset notifiers are designated for various issues related to unavailability or inappropriate functionality of the server or its closest network nodes. Like, for instance, the status code 504 notifier describes situations when the network gateway is not working properly, creating a timeout error response. Or the 500 coded notifier that states that there’s a problem with the internal server software configuration that keeps it inaccessible.

There are a wide range of scenarios when the website can’t be available for access externally. This includes, as it was specified earlier, issues with CloudFlare platform or connectivity between the service and the resource. Such instances need additional attention from webmasters due to the complicated nature of the network that was built with the use of the proxy.

All things considered, notifiers from the 5xx codeset mean that the user can’t get access to the resource and its content, be it a website, web app or something else. From the SEO standpoint, whenever the web resource displays such a notifier, it means that not only users, but also parsers from search engines won’t be able to reach the website. Therefore, there will be no incoming traffic and also no SERP promotion for the resource. And even if the instance is only temporary, its position in SERP rankings could and will become lower.

Why Are 5xx Status Codes Important for Webmasters?

Why Are 5xx Status Codes Important for Webmasters

Whenever the webmaster sees a returned 5xx codeset notification, it means that there are some serious issues with the resource that must be fixed fast, taking into account that users actually can’t reach it and get the expected response. Excluding maintenance routines, of course, because those must be resolved as fast as possible. 

Although usually such problems are easily solvable by webmasters, sometimes there are situations when they can’t fix the error by themselves. Take status code 502 as an example - it’s possible to fix it if the current root of the issue is in the configuration. But sometimes it depends on the ISP, and only the provider can actually fix it with the help of the webmaster.

Also, there are cases when there’s a misconfiguration or cache mismatch on the user-side. Like with the 501 notifier that states that the server has no such functionality that is included in the request. It could be caused by a variety of things on the user-side, from wrong header to outdated cache.

All things considered, it’s vital to remember that not only users won’t be able to get the website if they see the 5xx return. Also, search engines that literally work like any other client, will deem the website as inaccessible. And it will surely harm SERP ratings of the website from slightly lowering it to literally dropping it down, depending on how prolonged the issue will be.

How to Diagnose and Fix 5xx Status Codes

How to Diagnose and Fix 5xx Status Codes

Whenever the user’s request failed with status code 500 or another one from the same codeset, it means that the issue must be diagnosed correctly and fixed. Sadly, it can be a long process, because almost no client will notify you about the problem as soon as it starts. In the best case users will start doing it after a couple of hours. That’s when an automated monitoring routine for return notifiers will surely come in handy, so it should be set up before something happens and your website’s reputation and SERP ratings will go downhill.

As far as webmasters are concerned, there are some relatively good web-based services for monitoring. And HostTracker, for instance, is one of the best among them. It allows its users, namely webmasters, to conduct complex and fully automated monitoring, including checking the HTTP responses, round-the-clock without any need for external control. And as soon as the system notices the returned 5xx notifier or the one from another codeset, it will send a notifier to the webmaster, making it way faster to fix current problems.

And while the Host-Tracker platform permanently conducts checks with regular intervals, as soon as the webmaster receives a notifier about occurring troubles referring to 5xx codeset, there are three ways to fix them. The first one is to check the server status and configuration, the second is to test the network and contact the ISP if there are 502 or 504 notifiers, and the third one, in case of 520-530 codes, is to go through the first two and then contact CloudFlare support.


Taking everything above into account, there’s one thing that you should remember for sure if you’re a webmaster. If you want to maintain your resource’s accessibility for users and search engines, you should be wary of 5xx codeset notifiers, conduct an automated monitoring in search for them and know how to deal with them as quickly as possible. Only this way it’ll be possible to keep the website or other resource accessible and its SERP ratings high. Because otherwise your project’s inaccessibility times will be unwantedly high due to the high reaction time in case of emergencies.


What is status code 500?

Being the first among 5xx notifiers, this code means that there’s something wrong with the server’s settings and it makes the resource partially or completely inaccessible for users and search engines.

List of references to official HTTP documentation and webmaster resources

  1. RFC 2774 (An HTTP Extension Framework)

  2. RFC 6585 (Additional HTTP Status Codes)

  3. RFC 7235 (Hypertext Transfer Protocol (HTTP/1.1): Authentication)

  4. MDN Web Docs (Mozilla Developer Network)

  • Comprehensive explanations of HTTP status codes, including examples and use cases. It's an excellent resource for web developers and webmasters - https://developer.mozilla.org/en-US/docs/Web/HTTP/Status

       5. Web Server Documentation

  • Server-specific documentation (e.g., Apache HTTP Server Documentation, Nginx Documentation) often includes information on server behavior related to 5xx errors and customization of error responses - ttps://httpd.apache.org/docs/ and https://nginx.org/en/docs/

About author

Artem Prysyazhnuk
CEO and founder of HostTracker LTD. He's a passionate entrepreneur with a strong technical background in F#. Artem has been working in the software development industry for over 20 years.