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Have you ever come across a website that has failed to load? Then, you may have come across the 4xx family of status codes. Let’s look closer at the 400 Bad Request error, what causes it, and how you can effectively fix it.

What is 400 Bad Request Status Code?

The 4xx HTTP error codes are the client-side errors, and the different codes indicate the reason for the field request. A 400 Bad Request error is a standard hypertext transfer protocol (HTTP) status code. It indicates a problem with the client’s request to a web server. This error occurs when the server cannot process a request due to invalid syntax or corrupted data. 

In simple terms, when you try to visit a website, you are essentially sending a message to the website’s server asking for access. However, if the server does not understand or cannot process your request, it sends back a “400 Bad Request” code. This error page might look different depending on your browser. Sometimes, instead of showing the error code, your browser might display a blank page.

Additionally, it’s worth noting that the appearance of this error page can vary as it may be customized by the website’s hosting server. For instance, you may encounter a standard “400 Bad Request NGINX” error page. The reason behind encountering the 400 status code can vary, but typically, the stems from a problem within your browser or device. It is essential to understand and address the 400 Bad Request error for seamless internet browsing and website interaction.

Error Code 400 Bad Request error
Error Type Client-side
Error Variations HTTP Error 400

HTTP Error 400 – Bad Request

HTTP Status 400 – Bad Request

HTTP Error 400. The request hostname is invalid

400 Bad Request

400 Bad Request. Request Header or Cookie Too Large

Bad Request – Error 400

Bad Request – Invalid URL

Why Does the HTTP 400 Bad Request Error Happen?

Various reasons can trigger the 400 Bad Request error, even if this error is not specific to any browsing or operating system. Let’s understand some of the common causes why this error occurs:

  • URL String Syntax Error

The HTTP 400 error may arise from an inaccurately entered URL, improper syntax, or the inclusion of forbidden characters in the URL string. This can occur inadvertently, particularly if a URL has been encoded incorrectly. Considering the example URL below, which includes characters that the server cannot process, leads to our 400 Bad Request error:


Notice the additional “%” character after the word “malformed” in the URL. A correctly encoded space should be “%20” and not “%%20.” Furthermore, an illegal character such as “{”  can also prompt A 400 Bad Request error. For instance, the URL below contains such a character, leading to the same type of error:

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  • Corrupted Browser Cache and Cookies

Even with a perfectly accurate URL, the 400 Bad Request error might arise due to corrupted browser cache files or issues with expired or corrupted browser cookies. For instance, you might encounter a 400 status code when attempting to access the admin area of your WordPress site after a period of inactivity. 

This could be attributed to a corrupted cookie handling your login authentication data, failing to authenticate you as a valid user with admin privileges. This leads to the refusal of connection and triggers the HTTP Bad Request error code.

  • Oversized File Upload

A 400 Bad Request error may also surface when attempting to upload a file to a website that exceeds the server’s file size limit for upload requests. This limit is contingent upon the server’s configuration. 

  • Invalid Request Message Framing

Errors stemming from invalid request message framing can occur due to software bugs or data corruption, resulting in deviations that render requests unprocessable by the server. Such discrepancies may lead to communication breakdowns between the client and server, resulting in the HTTP status code 400 error.

  • DNS Lookup Cache

The occurrence of a 400 Bad Request error can be linked to the disparity between locally stored DNS data and the registered DNS information. DNS (Domain Name System) facilitates the translation of domain names into IP addresses, similar to a phone number dialing a specific server.

Initially, when you visit a website, a process called “name resolution” transpires, mapping the domain name to the server’s IP address. To speed up the process of subsequent visits, this information is stored in the local DNS cache, similar to how the browser cache operates for various files like HTML, CSS, and JavaScript.

  • Generic Server Error

Occasionally, this error can stem from server-side issues, indicating a broader problem with the server, a temporary glitch, or unspecified transient issues. If encountered while trying to connect to a third-party website, the resolution might lie beyond your control. Your best recourse would be to attempt browser refreshes.

To identify if it is a server-side issue, attempt to load the website on different browsers or devices. If the problem persists across different platforms, it likely originates from the server. In such cases, reaching out to the site owner with details of your operating system, browser, and versions could facilitate resolution.

  • Deceptive Request Routing

Misrouting of requests through networks can result in deceptive request routing, wherein client inputs are incorrectly directed or intercepted before reaching the intended server destination.  These discrepancies between client input and server reception can lead to errors, including the 400 Bad Request error, as the server may be unable to interpret a processed request accurately.

  • Website Misconfigurations

Although this is not a common cause and is highly unlikely, sometimes the problem may stem from an identified misconfiguration of a website, leading to the 400 code.

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How to Fix 400 Bad Request Errors?

Before troubleshooting the 400 error, you can start by refreshing the page or checking your internet connection. If the error still remains, you can implement the following methods to resolve the issue.

  • Check the Submitted URL

One of the most prevalent causes of 400 Bad Request errors is the URL itself. It is common to inadvertently include unwanted characters when manually entering the URL in the browser. Ensure that both the domain name and the specific page you are attempting to reach are accurately spelled and typed.

Additionally, confirm that they are properly separated by forward slashes. If the URL incorporates special characters, verify that they have been encoded correctly and are permissible URL characters. For lengthy URLs, consider utilizing an online URL encoder/decoder for enhanced accuracy and decreased risk of errors.

  • Double Check Domain Address

The Domain Name System (DNS) is responsible for translating user-friendly website names (domains) into server IP addresses. This eliminates the need for visitors to memorize lengthy strings of digits, allowing them to access your website using a simple, easy-to-remember name. Valid domain names consist of letters and a few specific characters, such as the fada characters (acute accent) and hyphens (dash). 

Domain names must have certain guidelines. They cannot exceed 63 characters, contain empty spaces, or begin or end with a hyphen. Inspect the website’s URL and ensure that there are no special characters or empty spaces in the domain section of the URL. Additionally, also check for the absence of a slash after the domain which can trigger the status 400 error Bad Request code.

  • Clear Browser Cache and Cookies

Clearing your browser’s cache and cookies can often resolve various issues, including the 400 response code. The browser cache stores locally some data files such as texts and images,  aiming to reduce server requests and speed up page loading. On the other hand, cookies track the user’s session history, login details, and preferences to offer a personalized browsing experience.

However, cache and cookies may become corrupted or outdated, leading to browser errors. Moreover, if the browser sends cookie data surpassing the allowed file size, it can trigger a specific status code like the 400 Bad Request- Request Header or Cookie Too Large. 

For Google Chrome users, follow the steps to clear cache and cookies:

  1. Click on the three dots in the top right corner of your browser and select Settings.
  2. Go to the Privacy and Security section and click on Clear browsing data.
  3. Ensure cached images and files as well as cookies and other site data are checked.  then, choose the desired time frame.
  4. Click on Clear data, and restart Google Chrome.

The process is similar for other browsers but may vary slightly in navigation. Note that clearing cache and cookies will sign you out of most websites and may reset some settings. Initially, websites might load more slowly as the browser needs to re-download content. Afterward, Try accessing the website again. If the 400 bad request error persists, consider exploring further troubleshooting methods.

  • Check Server Limit for File Upload
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Attempting to upload a file larger than the server’s limit can trigger the server error 400 code.  Start by uploading a smaller file to test. If successful, the original file might be too large, requiring compression before the re-uploading. Numerous online resources can assist in compressing larger images, video, or audio files.

  • Clear DNS Cache

Another common cause of a 400 bad request error is corrupted outdated local DNS lookup data. and like browser cache, local DNS data is stored by the operating system. Here are the methods to clear the DNS cache on various operating:

Windows 11:

  1. Right-click on the start menu and choose Windows terminal (Admin) or Command Prompt (Admin).
  2. Input “ipconfig/flushdns” into the command prompt window and hit Enter.
  3. A confirmation message will appear, indicating successful flushing of the DNS resolver cache.

This method of DNS cache flushing functions similarly on Windows 10, 8, and 7.

macOS Sonoma:

  1. Go to Applications -> Utilities -> Terminal. Alternatively, utilize Spotlight search (Cmd + Space) to locate it.
  2. Write “sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder” and press Enter.
  3. When prompted, input your administrator password. Note that it will not be visible as you type.

This command is effective in various prior versions, including macOS Catalina, Mojave, and High Sierra.

For Google Chrome users, clearing the outdated DNS cache in the web browser is necessary. Follow the below steps to do it:

  1. Input chrome://net-internals/#dns into the address bar and press Enter.
  2.  click on Clear host cache to flush the DNS cache within Chrome. 
  • Deactivate Browser Plugins and Extensions

If you have browser plugins and extensions installed that affect website cookies, they might be causing the issue. Try temporarily disabling them and then attempt to connect to the website again.

  • Contact the Website Administrator or Hosting Provider

If none of the above methods resolve the issue and other users are also encountering the same errors across different networks, it suggests a misconfiguration with the website. Reach out to the website administrators to report the error for investigation. If you manage the website, contact your hosting provider’s support team to further investigate the problem.


Thus, a 400 Bad Request error can occur due to a variety of reasons. A submitted request to the server or local caching issue causes this client-side issue. Implement the different methods for fixing this problem so that you or your customers can achieve a smooth user experience.