Fix Bad Request Error 400

What is a Bad Request Error 400 and How Do You Fix It?

Isn’t it super annoying when you’re caught up in a hectic routine and the website you’re using won’t load? How will you complete your online project or finish your research on time? It can disrupt your schedule and make working on a project very stressful.

People can deal with a slew of errors when using the internet. In this post, we will talk about error 400, one of many 4xx status codes. It restricts users from accessing the desired website or web resources.

We will take a comprehensive look at error 400. After that, we will discuss several methods to solve for the error 400 message.

So, let’s begin with a simple question: What is a bad request 400 error?

What is Error 400?

You can call it an error 400 message or 400: Bad Request. The error 400 also shows as “HTTP error 400” in some browsers but can be different for others.

The bad request error occurs when the server you’re trying to reach sees your access request as a general client error. Hence, it rejects and doesn’t verify your request. In turn, that leads to the error 400 response on your browser. 

It often shows when the server can’t categorize the error in other categories of status codes. It generates the “400 Bad Request” response on your browser. This error shows that the request you sent had some issues (i.e., the user) with the server before processing.

The server might classify it as a client-side generic error due to invalid request message framing, or even malformed request syntax.

Another possible reason for the 400 Bad Request error message is deceptive request routing. The server sees all those issues as client-initiated errors. The server cannot and will not process your access request in this case.

In most cases, a 400 Bad Request is due to client-side issues. However, it’s also possible that the server has encountered poor configuration or other problems.

Let’s take a look at some of the error 400 variants.

Multiple Variations of the Error 400

The error 400 is from the HTTP status code family. Therefore, it informs the user of why they can’t access a specific site. In rare cases, the error message may not show the error code, or the message may vary.

That’s because of the variations of the error of 400 message.

These variations of the bad request error 400 include:

  • Bad Request – Error 400
  • Bad Request – Invalid URL
  • 400 Bad Request
  • HTTP Error 400 – Bad Request
  • HTTP Error 400
  • 400 – Bad Request
  • Bad Request – Your browser has sent a request that this server couldn’t understand
  • 400 Bad Request – Request Header Or Cookie Too Large
  • HTTP Error 400 – The request hostname is invalid

Why Are You Getting an Error 400?

Your computer sends a request to a web server when you hit enter after typing in a URL. The server receives the request, reads and then verifies it. Then, it sends the requested web page back to you.

So, the error 400 occurs when the server sees an issue in your request.

It will neither process the request nor send the requested web resource. Instead, it will simply send an error message such as “400 Bad Request”. Here’re a few reasons why you might see error 400:

  • Malformed URL syntax
  • Outdated/corrupted DNS cache
  • Outdated browser cookies and cache
  • Large file size

6 Methods to Fix the Error 400

Here’s a useful tip before we dive into a few ways to solve error 400. It would help if you tried reloading/refreshing the page. Sometimes, the problems that deny your access request can fix themselves.

Don’t fret if a simple reload/refresh didn’t let you access the site or web resource. You can quickly try some of the following methods to fix error 400

1. Clear Outdated DNS Cache

Let’s look at it this way: your device quickly scans different DNS records when you go to a site. Your device searches for IP addresses, server names, and previously visited domain addresses/names in the DNS records. The content that your system is searching for in the DNS cache should relate to the domain name you’re trying to access.

Following that, your device clocks and stores the IP address of the servers in its DNS records. That way, your device doesn’t have to spend much time calculating and searching for a domain name match in the DNS cache.

Thereafter, subsequent visits to the site load even faster.

The main issue is that the DNS cache has pre-allocated space in your device’s internal storage. And if you visit a lot of different websites, your DNS cache will require manual clearance since it can become outdated or corrupted.

Due to a corrupted DNS cache, the server rejects your browser’s request as it appears to have an error. Thus, you see the error 400 Bad Request message.

You have to manually remove the corrupted/outdated DNS cache from your device to solve the issue.

You can find this DNS cache inside the operating system of your device.

Clear Outdated DNS Cache in Your MacOS X Device

  1. Press the F4 key on the keyboard/keypad
  2. Open the Terminal
  3. Run the command terminal
  4. Type the command “sudo killall -HUP mDNSResponder”

Clear Outdated DNS Cache in Your Windows 10 Device

  1. Go to the Windows Start Menu and right-click it
  2. Click on search and type “command prompt.”
  3. Run the Command Prompt 
  4. Type the command “ipcongif/flushdns”
  5. Press enter and wait until the process completes
  6. The message “Successfully flushed the DNS Resolver Cache” will appear if the action completes

Clear Outdated DNS Cache in Google Chrome

  1. Open Google Chrome 
  2. Without inverted commas, click on the address bar and type “chrome://net-internals/#dns” without inverted commas.
  3. Click on “Clear host cache.”

If you use any other browser, make sure you clear the outdated DNS cache in it to solve the error 400 messages.

You will also find a lot of repair tools for WordPress sites specifically. Such tools can help you solve many issues with your website if you’re an administrator.

2. Disable Browser Extensions

Disabling browser extensions is an often overlooked method to solve the error 400 Bad Request. You can try disabling or even removing the extensions you currently have. Once you do that, check if that resolves the issue.

Numerous browser extensions bring additional code into the browser’s working frame. That interferes with how the browser sends a request to a certain web server.

In short, your web browser extensions may be the main cause of error 400

Due to the extensions interfering with your browser’s request, the server may reject your request and not verify it. Moreover, a lot of extensions affect browser cookies and cache. That can also lead to the error of 400 messages.

Therefore, we recommend that you disable your browser’s extensions and check if that resolves the issue. Here’s how to do that in the Google Chrome browser:

  1. Run Google Chrome 
  2. Click the three-doted menu at the top of the browser (right side)
  3. Click on “More tools.”
  4. Select Extensions
  5. Manually disable all extensions by clicking on the on/off switch
  6. Refresh the web page or insert the URL once again
  7. If the issue doesn’t resolve, move to another method

If the browser extension triggers the error 400 messages, the web page will load normally. We advise that you narrow down your search for the culprit extension. Once you confirm that extensions triggered the error 400, find the one that’s responsible.

Turn on all the extensions once again and reload the page. If error 400 shows up again, start turning off the extensions one by one to find the one triggering the bad request error.

Disable these extensions, or remove them from your browser.

3. Cross-Check the Domain Address

We stated earlier that the HTTP 400 error occurs due to client-side mistakes. One of the biggest and most common mistakes is entering the wrong URL.

By typing the wrong URL to reach a certain website, you may trigger error 400.

You might have made a typo while entering the URL in the browser’s address bar. You may have a malformed syntax in the address. Similarly, you possibly inserted illegal or irrelevant characters when typing the URL. 

Make sure you check the spelling of the domain name you’re trying to reach. Pay attention if your URL contains a file name, query string, directory path, or special symbols.

Misplacing a single hyphen (-) is enough to trigger the error 400 messages.

A poorly encoded URL can also cause the error 400. The encoding process converts the URL into ASCII characters. That makes it easier to transfer the URL request over the internet to the server.

But a single misplaced character such as a double percentage sign (%%) instead of a single will fall under a malformed syntax error. That’s enough to trigger the error 400.

In short, you will receive the error 400 if you’re using a badly encoded URL.

4. Clean Corrupted/Outdated Browser Cookies and Cache Data

Your browser cookies store data about your behavior with several sites. They improve the user experience and site personalization so you can keep visiting them. The same goes for browser cache data.

The cache data stores information to help load sites faster. Those components include images and text.

Both cookies and cache data combine to provide a personalized browsing experience to the user. However, there’s one serious issue with both types of browsing features.

Cookies and cache can get corrupted or outdated.

Outdated cookies and cache are common causes of error 400. If your browser sends large cookie files, the server may respond with an error 400 “Bad Request” message.

To solve the error 400 and access the web page, you should clear outdated browser cookies and cache. 

Clearing Corrupted Cookies and Cache in Google Chrome:

  1. Click on the three dots at the top-right corner of Google Chrome
  2. Click on Settings
  3. Go to the “Privacy and Security” tab
  4. Select “Clear browsing data.”
  5. Check the boxes “Cached images and files,” “Cookies,” and “Other site data.”
  6. Click “Clear data” and wait for Chrome to finish the process

Note that following these steps will sign you out of several websites. You may also lose personal settings for a few.

Additionally, the loading time may increase slightly for several sites. Try the following method if clearing outdated cache and cookies doesn’t work.

5. Review and Ensure Proper File Size

Sending large files to the server will trigger error 400. You may encounter a “400 Bad Request” error message if your request exceeds the file upload limit of the server.

The simplest solution for this issue is to compress your files.

You can resize the large file to fit the upload size limit of the server. Nevertheless, resizing a file may result in lower quality. This is common for image and PDF files as the content can become unreadable and blurry.

6. Try Restarting PC or Relevant Hardware

As a last resort, restart your PC to solve the issue. Also, restart your network connection as it may also resolve the bad request error.

You can even try resetting your router or other connections.

Restarting your PC or internet hardware will clear up some storage on your Random Access Memory (RAM). By clearing space on your RAM, the error 400 issue may resolve.


You can try a combination of methods to solve the error 400 Bad Request message. If you keep experiencing the issue, try talking to an experienced professional. It’s a client-side issue most of the time, and that’s why it’s easy to solve.

A lot of client-side issues can interfere with the request you submitted. For example, there might be local caching issues with your request.

You can easily understand and use the methods above. They require minimal technical knowledge so you can resume your work in no time.

Leave a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.