HTTP 501 Not Implemented Error: What It Is & How to Fix It

500 internal server errors such as 502 Bad Gateway errors, 503 Service Unavailable errors, 504 Gateway Timeout errors, and 501 Not Implemented errors can have a serious impact on a website’s functionality. To prevent disruptions, improve SEO and rankings, and ensure a positive user experience, learning how to troubleshoot and fix these errors is a vital part of maintaining a website.

To help keep your website functionally properly, let’s look at everything you need to know about 501 errors, including what they are, what causes them, and how to prevent them.

What is a 501 Not Implemented error code?

501 Not Implemented is an HTTP status code indicating that the server does not support the functionality required to fulfill the request. The server may recognize the request method, but it isn’t able to carry out the action requested due to limitations in its functionality or configuration, displaying a 501 error response instead.

Common causes

There are a few different issues that can lead to 501 errors. One of the most common causes is an unsupported HTTP method or request header. For example, if the server does not support the PATCH method but receives a PATCH request from the client, it will respond with a 501 error.

Misconfigurations in the server setup and outdated server software can also lead to 501 errors. If the server is not properly configured to handle the request or lacks support for newer HTTP methods/protocols, then it won’t be able to process the client’s request.

Plugin conflicts and compatibility issues with the server environment can lead to 501 errors as well. Conflicts caused by things like outdated plugins or overlapping functionality can result in a variety of error types, with 501 errors being one of the most common.

Troubleshooting 501 errors

501 errors are something that you will want to fix as soon as possible, but given the fact that numerous things can cause them, troubleshooting these errors is often a process of trial and error.

To find out what’s causing a 501 error, here are the troubleshooting steps that you should follow:

Try reloading the page

The quickest and simplest solution is always the one you should try first, and reloading the page that returned the 501 error may fix the problem. If the error is caused by a temporary glitch or network issue, simply hitting the refresh button on your web browser will often solve the problem.

Review server logs and messages

You can get a lot of valuable information from server logs and messages regarding the root cause of a 501 error. Start by checking for messages related to the request that triggered the error, then look for details about which functionality or method the server doesn’t support.

Check for compatibility issues

Compatibility issues between the client and the server are often the cause of 501 errors. Check the compatibility requirements of the website or application you're trying to access and ensure that your browser, operating system, and network configuration are all compatible to see if this is causing the problem.

Check for software updates

501 errors are sometimes caused by outdated software that needs to be updated. Keeping your software up-to-date is a good practice even if you aren’t encountering 501 errors, and it’s certainly something you should do if you are.

Test with minimal configuration

Testing with minimal configuration is one good way to help isolate the cause of a 501 error. Whether on your WordPress site or other CMS platform, try disabling any unnecessary plugins, reverting to default settings, and simplifying your setup as much as you are able. If this fixes the error, you can re-enable components one by one, testing again after each, to see which one is causing the error.

How to fix 501 errors

Once you’ve identified the root cause of a 501 error, it becomes a lot easier to fix it. Depending on what is causing the error, here are the methods you can use to fix it:

Update software

We’ve already mentioned how out-of-date software can lead to 501 errors (among many other errors and issues). If you’ve managed to pinpoint the specific software causing the error, updating it to the latest version will often do the trick. And even if this isn’t causing the 501 error, updating any out-of-date software is still a good idea regardless.

Clear browsing data

Clearing your browsing data, including cookies and cache, will often resolve 501 errors. The reason is that cached data can sometimes become corrupted or outdated, which leads to errors when loading web pages. By clearing your browser cache and cookies, you can eliminate any corrupted or outdated data and ensure you’re using the most up-to-date version.

Disable proxy settings

If your browser is set up to use a proxy server, it may interfere with your ability to access certain websites and can trigger 501 errors. To see if this is the issue, try disabling proxy settings in your browser and attempt to load the page again.

Other methods

There are a few other things you can try that will often fix 501 errors. Implementing server-side optimizations, for example, can sometimes eliminate 501 errors (and improve your website’s overall performance too). You should also ensure your website’s code is clean and well-structured, as this will go a long way toward preventing errors.

Contact your hosting provider

If none of the methods listed above solve the issue, consider contacting your hosting provider for further assistance. They will have access to server logs and advanced diagnostics tools that can help identify the error’s root cause. To expedite the process, be sure to provide all the information you can about the error as well as the troubleshooting steps that you’ve already taken.

How to prevent 501 errors

Preventing 501 errors from ever occurring in the first place is a whole lot better than trying to fix them after the fact. Thankfully, there are several things you can do to improve your website’s performance and reduce the likelihood of 501 errors.

Regular maintenance and updates is an essential place to start. Things like vulnerability patching, ongoing monitoring, and regular updates are all major keys to preventing 501 errors and keeping your website healthy in general. It’s also a good idea to implement robust testing procedures so you can identify and address potential compatibility issues proactively.

Optimizing your website’s code via methods such as using a content delivery network (CDN) can also help. You should also strive to reduce your dependency on deprecated features and always adhere to website coding best practices.

Lastly, enhancing server security is key to preventing 501 errors (among a number of even bigger issues), and many of the steps taken to bolster a website’s security will improve its performance as well. Using a web application firewall (WAF), for example, will block malicious traffic and prevent it from harming your website’s functionality.

Sustain a healthy website with SiteLock

Encountering 501 Not Implemented errors can disrupt your website’s performance and leave your users frustrated with their experience. The good news is that these errors can almost always be fixed with the right troubleshooting steps. And, even better, there are also solutions you can use to prevent 501 errors outright.

If you would like to optimize your website’s security and performance to help prevent 501 errors and other issues, SiteLock can help! SiteLock provides comprehensive website security solutions for a range of CMS platforms, including WordPress and Drupal.

Be sure to check out how SiteLock works to learn more as well as our pricing page to see which plan is the best fit for your business.

Image by Gerd Altmann from Pixabay