How to Fix a 400 Bad Request Error: 8 Easy Methods

The 400 bad request error is an HTTP status code that describes an error caused by an invalid request. Thus, the server can’t understand and process it. Most HTTP error 400 bad requests are caused by malformed request syntax, invalid request message framing, or deceptive request routing.

If you’re browsing the internet and encounter this error, it’s possible to solve the problem easily. However, there are several occasions when the error comes from the website server. In this case, only the site owner can fix the problem.

This article will discuss eight methods of resolving a 400 bad request error. We will also cover the HTTP error 400 bad request message variations and their possible causes.

Error code400 Bad Request Error
Error typeClient-side
Error variationsHTTP Error 400
HTTP Error 400 – Bad Request
HTTP Error 400. The request hostname is invalid
HTTP Status 400 – Bad Request
400 Bad Request
400 – Bad Request. The request could not be understood by the server due to malformed syntax. The client should not repeat the request without modifications.
400 Bad Request. Request Header Or Cookie Too Large
Bad Request – Invalid URL
Bad Request – Error 400
Bad Request – Your browser sent a request that this server could not understand
Error causesBad URL syntax
File too big
Bad cookies or cache
DNS issues

“400 Bad Request Error” on Different Browsers

Just like a 404 error page, the 400 bad request page is customizable. For example, Google has a custom 400 bad request error page that looks the same on all web browsers.

Google 400 error page.

However, if the site doesn’t have a customized error page, the web browser will show the default one. Here is how the HTTP 400 bad request status code looks on different browsers:

Google Chrome

For 400 bad request, Chrome will show an error icon with The page isn’t working text followed by If the problem continues, contact the site owner. Then, you’ll find the HTTP ERROR 400 at the bottom of the message.

HTTP error 400 page on Google Chrome

Microsoft Edge

Microsoft Edge has a design almost identical to Google Chrome’s, with the HTTP ERROR 400 text at the bottom.

HTTP error 400 page on Microsoft Edge


The HTTP 400 bad request error in Opera displays the same text as Google Chrome. The only difference is the icon, as Opera uses its logo.

HTTP error 400 page on Opera

Mozilla Firefox

Mozilla Firefox will show a blank page when you try to access a website using the wrong syntax. There’s no text indicating that you encountered an HTTP 400 bad request error, which makes identifying the problem harder.

HTTP error 400 page on Mozilla Firefox


Like Mozilla Firefox, the browser will appear blank with no indication of the HTTP 400 bad request error.

HTTP error 400 page on Safari

Causes of the 400 Bad Request Error

When you try to access a website, your computer sends a request to the web server. Then, the server processes the request and sends back the page you want.

The error 400 bad request happens when the server can’t understand the request. Thus, it won’t process it and will send you the error code instead.

In most cases, client-side issues trigger the error. Some common causes of the 400 bad request error are:

  • Malformed URL syntax – the URL may contain invalid characters such as {, }, [, or ]. A wrongly encoded URL can also contain wrongly used ASCII characters, such as double percentage characters.
  • Large file size – websites have a file upload limit. An attempt to upload a file that exceeds this limit can be considered a bad request and trigger the HTTP 400 error status code.
  • Corrupted browser cookies or cache – expired cookies or corrupted browser cache may interfere with the request and trigger the error. This commonly happens on login pages such as the WordPress login page.
  • Bad DNS cache – if the website has moved to a new domain name or web host, the DNS cache data in your operating system may be invalid.

How to Fix a 400 Bad Request Error

The first action we recommend is refreshing the page. If that doesn’t work, then you should try the following methods.

1. Double Check the Domain Address

One of the most common causes of HTTP status 400 bad request error is a wrong URL. This may include a mistyped URL, malformed syntax, and illegal characters in the URL.

It’s easy to mistype a URL, so be sure to check the domain name spelling. If the URL contains a directory path, file name, or query string, pay attention to special symbols such as a hyphen (-) or percentage character (%).

For example, is the correct domain name. If you type in in the URL bar with an extra percentage character, it will result in a 400 bad request error.

Screenshot of HTTP 400 error page

A badly encoded URL can also cause this error. URL encoding converts characters into ASCII characters to make them transferable on the internet. For example, one of the most common encodings is replacing space with %20.

However, a URL can be encoded incorrectly and thus contain incorrect syntax, like double percentage characters (%%). If you enter a URL or click on a link that’s badly encoded, you’ll end up with a bad request error 400.

When encountering a 400 bad request error because of a wrong URL, use an encoder/decoder tool. Decode the URL and encode it again to make sure it is correct.

2. Search the Keyword

There may be cases where you are sure that the URL is correct, yet the error persists. If you know the title of the article or page you’re looking for, search the keywords on the website or a search engine. Sometimes you can even see the title on the URL.

For example, in the /tutorials/how-to-make-a-website URL, you’ll see the article’s title at the end of the URL. If the website has a search feature, type the keyword to find the article.

Alternatively, use a search engine like Google or Bing. To perform a search on a specific site, type site: followed by the website’s URL and the keyword.

For example, the title of the article is how to make a website. Therefore, you type how to make a website.

Google search query using site

3. Clear Browser Cache or Cookies

Browser cookies and cache store site data and content on the client’s side to improve the browsing experience.

The browser cache contains website files such as texts and images to reduce requests to the web server and make the page load faster. At the same time, cookies store the user’s session history and preferences to make personalized browsing possible.

However, cookies may expire after some time. Also, both the website cookies and cache can be corrupted and cause a 400 bad request error.

Additionally, HTTP status 400 bad request error can happen when the web browser sends cookie data that’s too large. In this case, the error message appears as 400 Bad Request – Request Header Or Cookie Too Large.

Try clearing your browser cache and cookies to solve this problem. If you’re using Google Chrome, here are the steps to do it:

  1. Click on the three dots on the top right corner of Google Chrome and select Settings.
Selecting Settings on Google Chrome
  1. Find the Privacy and security section and click on Clear browsing data.
Clear browsing data on Google Chrome
  1. On the Clear browsing data window, check the Cached images and files and Cookies and other site data and use the drop-down menu to select the time frame.
Clear browsing data on Google Chrome.
  1. Click Clear data and restart Google Chrome to finish the process.

Remember that clearing the browser cache and cookies resets the settings and signs you out of websites you’ve visited. Also, it will take more time to load the websites since the browser will need to retrieve the content previously stored in the cache.

If the cache and cookies were causing the 400 bad request error, you should be able to visit the website normally again. However, if it doesn’t work, try the next method.

4. Turn Off Browser Extensions

Browser extensions can also cause a bad request error 400. That’s because these extensions interfere with the request sent to the web server, which may lead the web server to interpret the request as invalid.

Moreover, browser extensions may affect cookies, which leads to a 400 bad request error. To find out if a browser extension is causing the problem, we recommend disabling all extensions first. Here are the steps for Google Chrome:

  1. Click on the three dots on the top right corner of Google Chrome. Select More tools -> Extensions.
Selecting extensions on Google Chrome
  1. Turn off all extensions individually by clicking on the switch button.
Disabling a Google Chrome extension
  1. Refresh the web page. If it loads normally, one of the extensions is causing the 400 bad request error.

After establishing that one of the extensions triggered the error, you need to identify the exact extension. Turn on the extensions one by one, refreshing the web page each time.

If you encounter a 400 bad request error after turning on one of the extensions, you’ve found the one causing the error. Keep the extension disabled or remove it altogether by clicking the Remove button on the extension settings page.

5. Check the File Size

Trying to upload a file that exceeds the server file size limit might trigger an HTTP status 400 bad request error. Sites usually have a different file upload limit, so check if the file you want to upload fits the limit.

If the website doesn’t mention the file limit, upload a small file to check whether that’s causing the error. If it works, then you should resize the file you originally wanted to upload.

Keep in mind that file compression may negatively affect its quality. If it’s a PDF or image, it can make the content blurry and unreadable. Be sure to check the quality of the file after compression and make sure that it’s still acceptable.

There are many free online compression tools so that you don’t need to install additional software on your computer. Some of the great examples are HiPDF for PDF files and UniConverter for video and audio files.

Wondershare HiPDF PDF compressor

6. Flush DNS Cache

When you visit a site for the first time, the system goes through a DNS lookup, which searches for the nameservers and IP addresses that are associated with the domain name.

Your operating system then stores the IP addresses of the web servers in the DNS cache. Therefore, the system can reduce the DNS lookup process on the next visit, making the site load faster.

However, a corrupted or outdated DNS cache can trigger the HTTP error 400 bad request. In this case, you need to flush the DNS cache.

Since the DNS cache is stored in the operating system, the methods to flush it may vary. If you use Google Chrome, you’ll also have to flush the DNS cache in the web browser.

Here are the steps to do it on Windows and Mac OS:

Microsoft Windows 10

  1. Right-click on the Windows Start Menu and select Search or use the search box in the taskbar if enabled.
Search feature on Windows 10
  1. Type command prompt and select the Command Prompt application.
Searching Command Prompt on Windows 10
  1. Type ipconfig /flushdns and press Enter.
Flush DNS command on command prompt
  1. You’ll see the Successfully flushed the DNS Resolver Cache message after the process is completed.
Successful DNS flush on command prompt

macOS X

Press the F4 key to open Launchpad and enter Terminal to open the command terminal. Run the following command if you use macOS Sierra, X El Capitan, X Mavericks, X Mountain Lion, or X Lion:

sudo killall -HUP mDNSResponder.

Google Chrome

  1. Type chrome://net-internals/#dns on Google Chrome’s address bar and press Enter:
  2. Click Clear host cache.
Clear host cache on Google Chrome.

If you use a different operating system, make sure to check our comprehensive guide on how to flush DNS cache.

7. Contact the Site Owner to Report the Error

If all attempts to fix the 400 bad request error didn’t work, there’s a possibility that the problem isn’t a client error but rather is a misconfiguration that the web owner needs to fix.

In this case, try to visit the contact page of the website and fill a contact us form, if available. Otherwise, most sites also have contact email addresses and social network accounts where you can inform them about the 400 bad request error.

8. Restart Your PC and Other Hardware

The last method is to restart your computer and network connection hardware, such as router and modems.

Restarting a PC often solves various problems, including the 400 bad request error because it clears the Random Access Memory (RAM). Moreover, it flushes the temporary cache that’s created as you open and close programs.

Temporary data from background processes may interfere with the request sent to the server, causing the 400 bad request error.


The HTTP status 400 – bad request indicates that the request sent to the server is invalid or corrupted. Just like other 4xx status codes, a 400 bad request is a client-side issue.

It can be caused by malformed request syntax, invalid request message framing, or deceptive request routing.

Since this is a client-side problem, users can easily resolve most of the 400 bad request errors. To recap, here are eight methods to resolve the error:

  1. Double-check the domain address.
  2. Search the keyword.
  3. Clear browser cache and cookies.
  4. Turn off browser extensions.
  5. Check and reduce the file size.
  6. Flush the operating system’s DNS cache.
  7. Report the error to the site owner.
  8. Restart the PC and networking equipment such as the router and modem.

If you have other tips or solutions, feel free to leave us a comment below.

400 Bad Request FAQs

Take a look at the following frequently asked questions about 010 Bad Request error.

What Are Some Best Practices for Avoiding a 400 Bad Request Error?

Ensure that all URLs and parameters are properly formatted and free of errors. Use HTTPS and secure authentication methods, such as cookies or tokens. Use cache headers to improve website performance and limit the use of redirects. Regularly monitor server logs for errors and unusual activity.

Are There Any Tools That Can Help Me Debug a 400 Bad Request Error?

Yes, there are several tools that can help you debug a 400 Bad Request error, such as browser developer or server log analysis tools. Apache Log Viewer or ELK Stack are examples of tools to help identify the root cause of the error and provide insights for resolving it.

The author

Leonardus N.

Leo is a WordPress fanatic and contributor. He likes keeping up with the latest WordPress news and updates, and sharing his knowledge to help people build successful websites. When he's not working, he contributes to WordPress documentation team and pampers his dogs.