How You Might See the 400 Error
400 Bad Request error messages are sometimes customized by website owners so keep in mind that this error may present itself in more ways than the common ones listed below:
"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 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, a 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 following 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 an HTTP status code that means that the request you sent to the website server (e.g. a request to load a web page) was somehow malformed therefore the server was unable to understand or process the request.
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
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 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. Specficially, 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.
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.
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 (next thing to try below).
Clear your browser's cache. A cached, but corrupt copy of the web page you're trying to access, but are getting the 400 error on, 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 so worth trying.
- While this is not a common fix, try troubleshooting 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.
- Contact the website directly that hosts the page. It's possible that the 400 Bad Request error actually isn't anything wrong on your end and it's something they need to fix, in which case letting them know about it would be very helpful.
See my Website Contact Information list for ways to contact a number of popular sites. Most sites have social network contacts and sometimes even telephone numbers and email addresses.
Tip: If an entire site is down with a 400 Bad Request error, searching Twitter for #websitedown, as in #facebookdown or #gmaildown is often helpful. It certainly won't contribute anything to fixing the issue, but at least you'll know you're not alone!
- If nothing above has worked, and you're sure the problem isn't with your computer, you're left with just checking back later.
Since the problem isn't yours to fix, revisit the page or site regularly until it's back up.
Still Getting 400 Errors?
If you've followed the advice above but you're still getting a 400 Bad Request error when trying to open a certain webpage or site, see Get More Help for information about contacting me on social networks or via email, posting on tech support forums, and more.
Be sure to let me know that the error is an HTTP 400 error and what steps, if any, you've already taken to fix the problem.
Errors Like 400 Bad Request
The following messages are also client-side errors and so are at least somewhat related to the 400 Bad Request error:
Server-side HTTP status codes also exist. You can see all of them in my List of HTTP Status Code Errors.