Best Ways To Fix The HTTP Error 400 On WordPress Websites

Fix The HTTP Error 400

What could be more annoying than getting an error page over and over again when you try to access a website? While most error pages get resolved with a simple page refresh or reload, most people wouldn’t even give another second of their life to wait and refresh your website if it throws error pages at them. That’s why every instance of an HTTP error counts – especially the persistent ones like the 4XX family of errors. 

Today, you are going to learn about one particular error message, the error 400 in detail, the causes, and most importantly, the ways to fix it. 

What Is A 400 Bad Request?

Most error codes indicate a problem on the server-side. Either the resource could be unavailable (404 – Page not found), or there could be internal server errors (500). But the 400 status code presents a generic error statement that indicates a problem from the client-side. This error code does not give any particular information on what could be the root cause, and the error page is usually a blank browser page with little to no information. 

 The 400 status code denotes a bad request where the server does not get to process the request. The error could be because of invalid request format, incorrect syntax, huge or invalid data,  deceptive request routing, wrong configuration settings, and more. 

How To Fix Error 400

Here is a list of some of the common root causes for the 400 bad request error

Syntax error in the URL string

An incorrect URL with typos or invalid data can cause a bad request that cannot be processed by the server. 

This is probably the most common cause as it is quite easy to type in the wrong characters in the URL by mistake and cause a malformed URL string. Invalid characters In the URL string can also similarly trigger the error. 


Make sure to type in the exact URL address and avoid inserting invalid special characters in your URL. Here are some tips to prevent URL errors

  • Double-check the URL for accuracy. For instance, an URL like is likely to suffer from spelling inaccuracy. Make sure you enter the correct URL.
  • Use shorter URLs. You can try URL shorteners to shrink your long URLs. 
  • Make use of online URL encoders and decoders to detect invalid characters. 

Bad browser cache and cookies

Corrupted files in the browser cache and cookies can easily lead to 400 errors. For instance, if your cookies are expired, and you try to use them to make a request, the request will be defined due to incompatibility in format or data validity. 

You may also face similar issues when trying to login to your WordPress site as an admin with corrupted cache data. 


Clear your browser cache, including all HTML docs, Js, CSS, media, and data files. You can do this by performing a hard refresh or clearing the browser data through browser settings. Cookies can also be cleared while  deleting your browser data. 

Outdated DNS cache

DNS  is necessary to perform the name resolution for every website you try to visit. This helps identify the actual IP address for the website domain name you are trying to reach. To help speed up the process, computers maintain a local DNS cache. 

When the local DNS data is not properly synced with the registered DNS information, your browsers might end up making requests to the wrong IP addresses.  


  • Flush your DNS cache by running a simple command in the command prompt: ipconfig/flushdns
  • In Mac systems, open terminal and run the command sudo killall -HUP mDNSResponder or try sudo discoveryuntil udnsflushcaches.
  • For Linux systems, use the command sudo systems-resolve –flush-caches. 

You can google up many more ways to flush your system DNS cache. 

Large file sizes

When your request contains large chunks of data that cannot be processed by the server, certain server configuration settings limit the size of file sizes. If your request exceeds this set limit, it can trigger an HTTP error 400


This issue is quite common among WordPress sites and is very easy to fix. Update your wp-config.php file to increase the file size limit. Look for the line with the statement, define(‘WP_MEMORY_LIMIT’,’64M’) and update it to a higher value like 256M. You can also maximize the file size limit in the .htaccess file and the functions.php file in the themes directory. 

Browser plugins or addons

Sometimes, the browser extensions and themes you use may meddle with the request format and add unnecessary junk or invalid data to the request.


Try deactivating the addons one by one to check if they are causing the problem. If so, either uninstall or update them with the latest version to fix the issue.

Other Fixes

Under rare occasions, the 400 error can also be caused by generic server errors or glitches. The best way to diagnose the error state would be to try and load the website in different browsers and see if the server can handle the requests coming in all the possible valid formats and browser agents. Identify the root cause, whether it is from the front end or back end coding and fix it as soon as possible to avoid any more downtime. 

If none of the fixes above seem to be working, it is time to knock the door of your web hosting service provider. Sometimes a hosting issue can mess up with the requesting routing ca. cause such errors. Make sure to contact the customer support of the web host and seek help to fix the issue as soon as possible. 

The Wrap Up

As important it is to improve your website accessibility, it is equally critical to fix HTTP error 400 to deliver flawless user-experience to your users. We hope this article would have provided you with the required solutions. 

Should you get stuck anywhere, write to us in the comments below.