What is a 400 bad request? Definition, causes and how to solve

What is a 400 error?

A 400 bad request error is when a browser sends a request to a web server and the server cannot understand or process it properly.

It is a type of http -svartatus code. And codes starting with 4xx usually indicate an error on the client page – which means the problem comes from what makes the request (browser, app, etc.).

There are many different message servers that use to indicate a 400 status code including:

• 400 bad request
• Http 400 bad request
• Http -Status 400 -bath -request
• 400 poor request error
• HTTP Error 400
• Bad Request: Error 400
• Http -error 400 -bath -request

The error looks like this one, depending on your browser:

Let’s dive into the common causes of 400 bad requests and how to solve them.

Http 400 error causes and how to solve them

Here are the most common causes of 404 bad request errors – and their solutions:

1. URL -Tring error or other invalid syntax

One of the most common causes of a 400 bad request error is a problem in the URL – as extra space or special signs such as “&”, “%” and “#.”

Sometimes the URL is too long and complex. Browsers have character limits (eg up to ~ 2,000 signs of chromium), and exceeding these limits can trigger 400 errors.

Errors may also be due to invalid syntax outside the URL that breaks standard rules.

This often happens when missing or wrong HTTP heading in the request prevents the server from interpreting or processing it.

E.g. Has the below get -request (which asks for data from the specified resource) a incorrectly formatted header:

In this case, the host head is missing a colon.

How to solve it

If you are a regular visitor to the site:

• Double control of the URL: Review the URL and remove any additional spaces, writing errors or invalid characters

For site owners and developers:

• Use a URL codes: If the URL contains special characters (eg
• Debug generated dynamically generated URLs: If you used an API or Script to automatically generate the URL, it may create links with incorrect parameter formatting, incorrect character coding or exceeded longitudinal bounds. Use a tool like Postman’s Link Checker to identify exactly what about your URL causing the problem.
• Use developer tools to identify the error: If you are not sure what causes the error, open your browser’s developer console (CRTL + Shift + I in Chrome), go to the “Network” tab, try the request and look for the red 400 error. Click it to see what causes problems.

2. Corrupt or invalid cookies

When cookies (small data files need to be stored on your device) Expire or be damaged, they can cause 400 errors.

How to solve it

If you are a regular visitor to the site:

• Clear cookies or go incognito: Clear your browser cache or launch a private session to remove existing cookies
• Disable extensions: Turn off temporary extensions that may interfere with cookies
• Check for browser updates: Make sure you use the latest version because outdated browsers can handle cookies differently

For site owners and developers:

• Confirm site code: If you are a developer or a site owner, check that your cookie implementation follows current standards and security practices. Meaning cookies need to use correct syntax, security settings and domain settings (rules that determine which sites can use the cookie) and remain below the 4KB size limit.

3rd browser extensions

Browser extensions can interfere with how your browser communicates with site servers in ways leading to 400 bad requests.

For example, ad blockers may prevent necessary manuscripts that a site requires to work properly from loading. Or extensions of privacy may change or block cookies that the site needs to properly process a request.

How to solve it

• Disable and Check Extensions: Turn off all extensions, then activate them one by one to identify the guilty and check the extension’s settings
• Update extensions: Click the Extensions icon in your browser toolbar. Then look for update options to get the latest version. In Chrome, switch with “Developer Mode” and click “Update”The button.

4. Outdated DNS -Cache

The domain name system (DNS) translates domain names (such as “www.yoursite.com”) to IP addresses (eg 192.168.1.1).

Your device saves these items in its DNS cache. But these items can be outdated if a site IP address changes.

When this happens and you visit the same site, your computer sends the request to the old IP address that is no longer found in place of the new IP address.

How to solve it

To remove outdated items that could cause 400 errors, rinse your DNS cache.

How to do it on Windows:

Open “Start“Menu and write” CMD “in the search box.

Click on “With“ Command Prompt ”selected“ Click ”Run as administrator. “

You may be asked to give access. In that case, choose “Yes. “

In the Command Prompt window opened, enter the “IPConfig /FlushDNS” command and press the “Enter” key.

Then you see a message confirming that DNS -Solver -Cache has been flushed successfully:

Now try to access the page again to see if the problem is resolved.

5. Server problems

Sometimes 400 errors can actually be caused by the server. This happens when the server is configured incorrectly and interprets valid requests as invalid.

For example, a server can be set to reject requests containing certain words that it incorrectly identifies as security threats. Or it may have outdated rules that do not work with modern browsers.

How to solve it

If you are a regular visitor to the site:

• Contact the site owner or support team to report the question
• Try to access the site later as temporary server problems often resolve on your own

For site owners and developers:

• Server error files: Review web server logs for specific details of what triggers the 400 errors
• Configuration files: Investigate Server Configuration Files (such as .htaccess for Apache or NGINX.CONF for NGINX) for errors or rules that may be too restrictive
• Adjust security settings: Disable or temporarily changes the rules of web application to see if they are blocking legitimate traffic
• Check server resources: Make sure your server does not run out of memory or treatment effect, which may cause it to reject requests it would normally accept
• Update server software: Make sure you are running the latest version of your web server software to avoid known errors that can cause 400 errors

6. Limits of file size

A common reason for getting a 400 error is if you try to upload a file that is too large for your site.

For example, uploading an image, video or document file above the size limit to a WordPress site can lead to a 400 error.

In WordPress you can check your file size limit by clicking on “Media“>”Library,“And then”Add New Media File“In the left column.

You then need to see something similar:

How to solve it

Reduce file size to below your limits to ensure that the server can fill your request.

Be hosting your videos on YouTube or Vimeo, uploading your audio files to SoundCloud, or compressing your images using a tool as a compression image to easier to stay within your limits.

Find & Fix 4xx Error on your site

Ideally you want to revise your site to find errors like 400 bad requests beforeThey affect performance and annoy the site visitors.

SEMRUSHS SEBTIENCE ADDITIONAL TABLE CAN HELP.

Open the tool, follow the configuration settings and go to ”Question“Type. Type” 4xx “in the search box to find a list of 4xx errors, and then click the pages.

You will find a list of the affected pages and their error codes (the tool shows more than just 400 errors):

Then apply what you learned in this article to resolve the errors.