How to Fix a 400 Bad Request Error

Methods to Fix a 400 Bad Request Error

 The 400 Bad Request error is an HTTP status code that means that the request you sent to the website server, often something simple like a request to load a web page, was somehow incorrect or corrupted and the server couldn't understand it.

400 Bad Request errors appear differently on different websites, so you may see something from the short list below instead of just "400" or another simple variant like that:

How You Might See the 400 Error

• 400 Bad Request
• Bad Request. Your browser sent a request that this server could not understand.
• Bad Request - Invalid URL
• HTTP Error 400 - Bad Request
• Bad Request: Error 400
• HTTP Error 400. The request hostname is invalid.
• 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.

The 400 Bad Request error displays inside the internet web browser window, just as web pages do. 400 Bad Request errors, like all errors of this type, could be seen in any operating system and in any browser.

In Internet Explorer, "The webpage cannot be found" message indicates a 400 Bad Request error. The IE title bar will say HTTP 400 Bad Request or something very similar to that.

Windows Update can also report HTTP 400 errors but they display as error code 0x80244016 or with the message WU_E_PT_HTTP_STATUS_BAD_REQUEST.

A 400 error that's reported for a link within a Microsoft Office application will often appear as a The remote server returned an error: (400) Bad Request. message within a small pop-up window.

Cause of 400 Bad Request Errors

The 400 Bad Request error is often caused by entering or pasting the wrong URL in the address window but there are some other relatively common causes as well.

Note: Web servers running Microsoft IIS often give more specific information about the cause of a 400 Bad Request error by suffixing a number after the 400, as in HTTP Error 400.1 - Bad Request, which means Invalid Destination Header. You can see a complete list here.

How to Fix the 400 Bad Request Error

1. Check for errors in the URL. The most common reason for a 400 Bad Request error is because the URL was typed wrong or the link that was clicked on points to a malformed URL with a specific kind of mistake in it, like a syntax problem.
   
   Important: This is most likely the problem if you get a 400 Bad Request error. Specifically, check for extra, typically non-allowed, characters in the URL like a percentage character. While there are perfectly valid uses for something like a % character, you won't often find one in a standard URL. 
2. Clear your browser's cookies, especially if you're getting a Bad Request error with a Google service. Many sites report a 400 error when a cookie it's reading is corrupt or too old. 
3. Clear your DNS cache, which should fix the 400 Bad Request error if it's being caused by outdated DNS records that your computer is storing. Do this in Windows by executing ipconfig /flushdns from a Command Prompt window.
   
   Important: This is not the same as clearing your browser's cache. 

1. Clear your browser's cache. A cached but corrupt copy of the web page you're trying to access but find the 400 error could be the root of the problem. Clearing your cache is unlikely the fix for the majority of 400 bad request issues, but it's quick and easy and worth trying.
    
2. While this is not a common fix, try trouble shooting the problem as a 504 Gateway Timeout issue instead, even though the problem is being reported as a 400 Bad Request.
   
   In some relatively rare situations, two servers may take too long to communicate (a gateway timeout issue) but will incorrectly, or at least unhelpfully, report the problem to you as a 400 Bad Request.