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400 Bad Request Error: What is it, What Are the Causes, and How to Fix It?

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When you want to access a website and it takes too much time and then doesn’t load despite having a very good wifi connection, it’s just frustrating. Well, website owners often face this kind of problem and should know what causes this and how to solve it.

400 Bad Request Error: What it is and how to fix it

Your server shows a specific status code for indicating that particular type of problem. The page not opening problems are generally related to the 4xx family of status codes. One of them is 400 Bad Request Error. 

In this article, I will discuss this particular status code error, its causes, and how to fix it with simple steps.

What is a 400 Bad Request Error?

When a website runs on a server, there are continuous client-server interactions that allow the site to respond to a request in a particular way. In response to an action, the server displays HTTP status codes. 

The 400 Bad Request Error is also an HTTP response status code. It indicates that the server was unable to understand or process the request you or the client sent due to some malformed or invalid syntax. 

As a result, the server refuses to service that request, and the site doesn’t load properly.

Is it only a Client-Side Issue?

Almost all the HTML status codes that fall in the 4xx category are considered client-side issues. On the other hand, the error response codes in category 5xx are considered server-side issues. But this is not always true.

There might be some cases where the server is producing the 400 error but the client may not directly be causing the issue or there is no client-side error. This cause is called generic server error. Though in any 4xx category error, the client has the issue in some way.

What are the causes of 400 Bad Request Error?

There are multiple reasons for this error response code. I am discussing them below.

1. URL String Syntax Error

It is a very common mistake and often the cause of 400 Bad Request Error. It’s due to an incorrectly typed URL or if the URL contains any illegal character or unrecognizable characters or if it has malformed syntax.

URL String Syntax Error

If your page URL contains any of these, the server would not understand the request and it will show this HTML response error code. For example, a link that contains two consecutive percentage characters “%” will be considered malformed and if the URL contains some illegal character like ‘{‘ or ‘^’ the link will be invalid.

Generally, in most URLs, these 84 legal URL characters are used “ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~:/?#[]@!%%EDITORCONTENT%%amp;'()*+, =”;.

2. Corrupted Browser Cache and Cookies 

Another way 400 Bad Request Error can occur is due to corrupted browser cookies or corrupted files in the browser cache.

Corrupted Browser Cache and Cookies

Websites use HTTP cookies for giving you a faster, smoother, and customized web visit and it partially remembers your last visit. So, whenever you visit a new site and accept the cookie policy, the site sends small file packages or cookies to your device and stores them temporarily so that it can use that data during your next visit on the site to load faster and give better user experience and performance.

But if the current website cookies are somehow corrupted or expired, it may lead to the connection being refused and cause 400 Bad Request Error.

It often happens when the owner tries to access the admin area of a WordPress site and the cookies that keep the admin authentication data are corrupted. As a result, it refuses to authenticate the user as the admin and 400 Bad Request Error is displayed by the server.

3. File Size Too Large

When you try to upload a very big file to a website, it may show 400 Bad Request Error. Each server has its file size limit for which it allows uploading. If the file size is greater than the maximum upload file size limit, the server will deny the request and show 400 Bad Request Error.

File Size Too Large

4. DNS Lookup Cache

When you first visit a website, a lot of procedure is running behind and its called “name resolution” that takes a little time. So, to boost the speed, many details like domain names and IP addresses are stored locally on your device in the local DNS Cache.

DNS Lookup Cache

Now if the DNS Cache is not synced with registered DNS information, it may cause 400 errors. So, make sure that the DNS cache is synced.

5. Generic Server Error

As mentioned before that not all 4xx code error codes need to be client errors. Some of them happen because of some kind of server-side problem also. Whether it is a glitch from the client-side or an error due to mentionable or a general problem with the server, it might show 400 Bad Request Error.

Generic Server Error

It is not much you can do in this case. But you can refresh the page or visit after some time interval. To check if it is a server-side error or not, you can use different browsers or different devices.

How to Fix the 400 Bad Request Error?

Well, it is often very difficult to find exactly the correct cause of the issue on your own. So, this solution includes many subsets or multiple steps that will diagnose and fix the problem. Just follow the steps mentioned below and your problem should be solved.

1. Check the Submitted URL

It is one of the most obvious and effective solutions as people often enter the wrong URL or insert some unwanted character in the link. It happens especially when someone tries to enter the URL manually by typing.

Check the Submitted URL

Check if the URL is correct and the domain name, the forward slash is at the right place. Also, don’t forget to check if there are any illegal or special characters. Though you might face problems with the long URLs. In that case, you can take the help of an online encoder/decoder.

If the URL is correct and it’s still showing 400 Bad Request Error, follow the next step.

2. Clear Browser Cache

Sometimes locally stored files in your browser cache become corrupted and may generate an invalid request message or 400 Bad Request Error. So, clearing the browser cache may be an effective solution.

Clear Browser Cache

For different browsers the options are different but in major browsers, you will find an option to clear browsing data in “settings” or “tools”. Then it will give you options on which type of data you want to delete. Now choose the cached images and files and click “clear data”. You can also clear all locally stored files to be on the safer side.

If this doesn’t solve the problem, follow the next step.

3. Clear Browser Cookies

As mentioned before, expired or corrupted cookies can often cause a 400 – Bad request Error. If your facing this problem with an error message and the previous two solutions did not work, try deleting browser cookies.

Clear Browser Cookies

Every browser has different options for clearing cookies. For clearing browser cookies in Microsoft Edge, go to settings and then go to “cookies and site permissions”. Now click “see all cookies and site data” and click the remove all option on the right-hand corner. You can also make some changes to the default settings to periodically clean the browser data.

4. Check the Upload File Size

If the size of the file you are trying to upload on the website exceeds the maximum file size limit the server allows, the server will deny that upload request and show 400 Bad Request Error messages.

Check the Upload File Size

In this case, you can compress the file using online tools and then upload it. To know if the server file size or server limit is the issue or not, try uploading smaller size files. If you succeed then the initial file size is the issue here.

5. Clear DNS Cache

Corrupted or unsynced DNS Cache files also triggers 400 Bad Request Status code. So, clearing outdated DNS records may help fix the problem.

Clear DNS Cache

Remember, DNS Cache data record is not stored by the browser. It is stored in the OS or operating system of your device.

6. Deactivate Browser Extensions

If you have installed many extensions in your browser and face a 4xx status code error, you should consider checking if any extension is causing corruption to the browser cookies. 

Deactivate Browser Extensions

To solve this, disable all the extensions and try accessing the website using a stable network connection. If an extension was causing the problem, it will fix it.

If you liked the article, comment down below and share it with your friends. Thank you for visiting us, have a nice day.

Author avatar
Tim Michaels
I am into WordPress and web development for the last 10 years. I use my experience to help people just starting with WordPress. Follow my blog at WP Uber for everything related to WordPress.
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