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400 Bad Request Error

Published on April 16, 2019

What is a 400 Bad Request error?

The 400 Bad Request error is an HTTP response status code that indicates the request cannot be completed. As with all 4xx errors, this is due to a perceived client error, which prevents the receiving server from processing the bad request. There are many factors that can contribute to the server interpreting the request as bad. For example, according to RFC 7231, this can occur because of malformed request syntax, invalid request message framing, or deceptive request routing.

The HTTP response status code will always remain the same, but the exact error page received will vary depending on the requesting client (e.g. web browser) and responding server. You may see the 400 Bad Request error in one of the following formats:

400 Bad Request
HTTP Error 400. The request hostname is invalid.
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
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.

Although each format may very slightly, they all mean the request cannot be successful until the client makes a modification and fixes the cause of the error. However, it is important to consider that even though the 400 Bad Request error is classified as a client error, it is still possible the issue is originating from the responding server.

Fixing a 400 Bad Request error

To fix a 400 Bad Request error it is best to start diagnosing the issue from the client side. This means troubleshooting from the device making the request, such as your web browser. Begin by completing one step at a time before making the request again:

  1. Verify the URL is correct
  2. Clear your browser's cookies
  3. Clear your browser's cache
  4. Clear your DNS cache

If completing the steps above does not resolve the 400 Bad Request error then you may want to check if any browser extensions or add-ons are the cause. This can be verified by temporarily disabling one extension or add-on at a time before making the request again. If the 400 Bad Request error continues you will want to contact the website associated with the error.


The 400 Bad Request error occurs when a server will not process a request that has been made. This is most often associated with an incorrect URL or expired cookies. This error can typically be resolved by simply verifying the URL is correct or clearing your browser's cookies. After exhausting all of the client side troubleshooting steps the next best step is to contact the website where the error is occurring.

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