Understanding The Web Server 400 Error Code

What is a Web Server 400 Error Code?

When browsing the internet, you may have come across a frustrating error message that says something like “Error 400: Bad Request” or “400 – Request Header or Cookie Too Large.” These error codes are part of the HTTP status codes, and specifically, the 400 series codes. The 400 error code indicates that the client’s request to the server was invalid, meaning that the server could not understand or process the request.

Common Causes of Web Server 400 Error Code

1. Malformed Request

One common cause of the web server 400 error code is a malformed request. This means that the client’s request was improperly formatted and couldn’t be understood by the server. It could be due to missing or incorrect syntax, invalid characters, or incomplete data in the request.

2. Invalid URL

Another reason for the 400 error code is an invalid URL. If the client entered an incorrect or non-existent URL in the browser’s address bar, the server won’t be able to find the requested resource and will respond with a 400 error.

3. Request Size Limit Exceeded

Some servers have limitations on the size of the request they can handle. If the client’s request exceeds this limit, the server will respond with a 400 error code. This can happen when uploading large files or sending extensive form data.

4. Cookie Issues

Cookies are small pieces of data stored on the client’s computer by websites. If the client’s request contains cookies that are too large or corrupted, the server may reject the request and return a 400 error code.

5. Browser Cache Problems

Browser cache stores temporary data to improve website loading speed. However, if the cache becomes corrupted or outdated, it can cause issues with the client’s requests. Clearing the browser cache can often resolve the 400 error code.

How to Fix Web Server 400 Error Code

1. Refresh the Page

One of the easiest and quickest ways to fix a 400 error code is to refresh the page. Sometimes, the error occurs due to a temporary glitch, and a simple refresh can resolve the issue.

2. Double-Check the URL

If the error persists, double-check the URL you entered in the address bar. Make sure it is spelled correctly and leads to a valid resource. If there is a typo or mistake, correct it and try again.

3. Clear Browser Cache

If you suspect that the browser cache is causing the issue, clearing it can help. Go to your browser settings, find the option to clear cache and cookies, and proceed with the clearing process. Afterward, try accessing the website again.

4. Check Request Syntax

If you are a developer or have access to the request code, review the syntax to ensure it is correct. Look for any missing or incorrect syntax, invalid characters, or incomplete data. Making necessary adjustments can resolve the 400 error.

5. Contact the Website Administrator

If you continue to encounter the 400 error code on a specific website, it may indicate a server-side issue. In such cases, contact the website administrator or support team and provide them with the details of the error. They will be able to investigate and resolve the problem.


The web server 400 error code indicates an invalid request made by the client. It can be caused by various factors such as malformed requests, invalid URLs, request size limit exceeded, cookie issues, or browser cache problems. By following the suggested fixes, you can troubleshoot and resolve the 400 error code, allowing for a smooth browsing experience.

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