Status Code 400

A status code 400 or a three-digital code beginning with 4xx indicates a client error. When the client sends a request to the server that is corrupted or faulty, the server issues a status code 400. It is important to fix 4xx errors on a website so that users can still access all the content on a website.[1]


A status code 400 or the 4xx class is intended to draw attention to errors caused by requests from the client (bad request). In order to identify the faulty access as precisely as possible, the server in question should issue the exact 4xx code in the case of an unsuccessful request.

List of all 4xx status codes[edit]

Errors with the status code 400 are listed below chronologically with the corresponding explanation:

* 400: All errors with the status code 4xx indicate a faulty request.

* 401 unauthorized: This request to the server requires the client to authorize. This is usually done by logging in. If a user still wants to access the password-protected resource, the status code 401 (unauthorized) appears with a note on what to do.

* 402 payment required: This status code is not yet used. In the future, it will indicate that you have to pay a fee in order to view the content and that it will only be visible after payment.

* 403 forbidden: This status code differs from a 401 error in that access is denied even with valid login data. This is happens, for example, when a site is requested with HTTP, but is configured with https.

* 404 not found: One of the most frequently displayed status codes is the 404-error. It is used to indicate that a requested link does not exist or does not exist anymore (dead link). If an error page displays a status code that differs from the 404 code, you get a “soft 404-error.”

* 405 method not allowed: The request was made using the wrong method. Which method is required, such as GET, is explained by the response within the error code.

* 406 not acceptable: In this case, the format requested by the client cannot be issued by the server. The content type is available in the server response.

* 407 proxy authentication required: Similar to status code 401, the server requests authentication by the client. Here, however, in relation to the proxy server being used.

* 405 request time-out: This code is displayed if the client could not send a complete request in the time period defined by the server.

* 409 conflict: This request by the client is rejected by the server because it was submitted under a false assumption. This status code may get output if the resource has changed.

* 410 gone: If the user receives this status code, it means that the resource is no longer available and/or has been deleted.

* 411 length required: If this code appears, the content length needs to be specified in the header to process the client request.

* 412 precondition failed: In this case, the prerequisite has been defined in the request, which does not apply. (for example, an if match)

* 413 request entity too large: This status code indicates that the request was too big to be processed by the server in question. The server response may include the instruction to try again later.

* 414 request-url too long: The server cannot respond because the URL is too long. This is usually caused by too many diversions.

* 415 unsupported media type: This request cannot be answered because the media type is not available.

* 416 request range not satisfiable: This error code indicates that a portion of the requested resource that is no longer available or invalid.

* 417 expectation failed: This code will be output if the “expect” field of the header specifies a particular request that the server that cannot fulfill.

* 422 unprocessable entity: This code indicates that the request cannot be processed. This may possibly be caused by semantic errors, but not media type errors as is the case with 415.

* 423 locked: This code means that the requested resource is temporarily locked and not accessible.

* 424 failed dependency: If this status code is issued, two requests were made. The second request depended on the first, but it was not successful.

* 426 upgrade required: In order for the server to handle this request, the client must use TLS 1.0.

* 428 precondition required: In order to execute this request successfully several preconditions should have been fulfilled.

* 429 too many requests: This code is issued by the server if it received too many requests from a client within a certain period of time. This may occur, for example, if an SEO tool queries too many keywords on Google within a short period of time.

* 431 request header fields too large: If the length of the header field or the entire header has been exceeded, this status code appears.

Avoiding errors[edit]

Errors with the status code 400 are often due to the configuration of the web browser. Therefore, users should check which websites issue these errors. Moreover, the server may deliver a 400-error code if the user entered a character into a form field that was not provided for. Therefore, if you receive a user error with status code 400, you should modify your software or its inputs.

Solutions for 404-errors[edit]

The classic 404-error is equally annoying for webmasters and users. Because 404-errors accumulate, this is not only a sign for a badly maintained website to users, but also to search engines. It would be advisable to create a special 404-error page so as not to adversely affect usability.

Humor is often used on 404-error pages. This will animate users and encourage them to search for the desired content on the target page.

A further possibility is to provide a search bar right on the 404 page, so that the desired information can still be found. Alternatively, it is possible to list similar topics.

Below are 7 specific tips of what a 404-error page should contain:

  • Polite or humorous apology for the mistake
  • Alternatives to the desired page, the desired product (for example, online stores), or alternative articles (such as blogs)
  • Option for the user to report the error so that it can be removed
  • Direct reference to the main navigation
  • A separate search bar to search for further content
  • Design of the error page to conform to the corporate design so that it is not perceived as a foreign object
  • Contact options

If you manage to keep the visitor on your website despite a 404-error page, the purpose of a proper 404-error page would be achieved and it would decrease the bounce rate and possibly still make a conversion.


  1. RFC2616-sec10 Accessed on 29/05/2014

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