Internet, Networking, & Security Browsers How to Fix a 400 Bad Request Error Methods to fix a 400 Bad Request error By Tim Fisher General Manager, VP, Lifewire.com Tim Fisher has 30+ years' professional technology support experience. He writes troubleshooting content and is the General Manager of Lifewire. our editorial process Facebook Twitter LinkedIn Tim Fisher Updated March 10, 2020 Browsers Chrome Safari Firefox Microsoft Tweet Share Email 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. 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. 400 Bad Request errors, like all errors of this type, could be seen in any operating system and in any browser. 400 Bad Request Errors 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: 400 Bad RequestBad Request. Your browser sent a request that this server could not understand.Bad Request - Invalid URLHTTP Error 400 - Bad RequestBad Request: Error 400HTTP 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. How to Fix the 400 Bad Request Error Lifewire / Jon Marchione 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. 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. 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 Clear your DNS cache, which should fix the 400 Bad Request error if it's being caused by outdated DNS records that your computer is storing.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 this command from a Command Prompt window: ipconfig /flushdns This is not the same as clearing your browser's cache. Clear your browser's cache. A cached but corrupt copy of the web page you're trying to access could be the root of the problem that's displaying the 400 error. Clearing your cache is unlikely the fix for the majority of 400 bad request issues, but it's quick and easy and 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 unconstructively, report the problem to you as a 400 Bad Request. If you're uploading a file to the website when you see the error, chances are the 400 Bad Request error is due to the file being too large, and so the server rejects it. If the site permits it, compress the file to a ZIP file and then upload that instead. If the 400 error is happening on nearly every website you visit, the problem most likely lies with your computer or internet connection. Run an internet speed test and check it with your ISP to make sure everything is configured correctly. 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 but is instead something they need to fix, in which case letting them know about it would be very helpful. See our 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. If an entire site is down with a 400 Bad Request error, searching Twitter for #websitedown is often helpful, like #facebookdown or #gmaildown. 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. More Ways You Might See a 400 Error 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. 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. Here's a complete list: Microsoft IIS 400 Error Codes 400.1 Invalid Destination Header 400.2 Invalid Depth Header 400.3 Invalid If Header 400.4 Invalid Overwrite Header 400.5 Invalid Translate Header 400.6 Invalid Request Body 400.7 Invalid Content Length 400.8 Invalid Timeout 400.9 Invalid Lock Token More information on these IIS-specific codes can be found on Microsoft's The HTTP status code in IIS 7 and later versions page. Errors Like 400 Bad Request A number of other browser errors are also client-side errors and so are at least somewhat related to the 400 Bad Request error. Some include 401 Unauthorized, 403 Forbidden, 404 Not Found, and 408 Request Timeout. Server-side HTTP status codes also exist and always start with 5 instead of 4. 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