What is an error code?

When you type in a URL or click a link on the internet, you are telling your browser to retrieve the information about that page and load it. To do this your browser sends a request for the information to the web server hosting that website and then re-interprets what it gets back into the page you see. However, naturally, things sometimes go awry. When this happens the browser displays an HTTP error (or status) code to give the user some indication of what went wrong. Below is a list of common error codes you might receive and a short explanation of what they mean.


Probably the most common error code you'll come across.
Probably the most common error code you’ll come across.


List of common error codes:


300: Maximum redirects have been reached
This error is given when a page you have tried to look at is redirecting to another, which is then in turn redirecting to a different page, and so on, five times. This is a safety measure put in place to prevent loops of infinite redirects and a subsequent browser crash.


400 Bad Request: The request cannot be fulfilled due to bad syntax
This error means that a mistake has been made in the request for information sent by the browser. This is usually a typo in the URL or because a link is missing an important element telling the server what to look for.

401 Unauthorized: Authentication is required and has failed or has not yet been provided
This means you have tried to access a part of the website that requires you to login first. If you have logged in but still receive this message, it could be related to a syntax error in the URL similar to the 400 error above.

402 Payment Required
This error code is rare and was originally designed for use in case online currency was ever introduced. Sometimes it can be caused by excessive requests from the same computer.

403 Forbidden: The request was a valid request, but the server is refusing to respond to it
If you see this error code it effectively means there is no way you will get to see the page. It is set as off-limits to everyone except the web administrator. This usually occurs if you’re trying to access something that isn’t a specific webpage, but a directory or some other form of information on the web server not designed to be seen by the public.

404 Not Found: The requested resource could not be found but may be available again in the future
This is one of the most common errors and means that you tried to access a page that doesn’t exist. The problem is most likely either a typo in the URL or that the page has been moved to a different location. If you followed a link and got this error it means the webmaster hasn’t updated the link or set it to redirect to the new page. This error can also sometimes just occur from a short period of server downtime or another simple problem and can often be solved by a simple page refresh.

405 Method Not Allowed: A request was made of a resource using a request method not supported by that resource
This is an uncommon error, and occurs when you’re trying to make a request of the web server without authorization. All 405 errors are related to web server security. Sometimes they can be caused by your Internet Service Provider preventing the correct information being sent to the web server.

406 Not Acceptable: The requested resource is only capable of generating acceptable content
This is another unlikely error code. It occurs when the web server tries to send information to the browser which it is unable to accept. All modern browers avoid this problem. If you’re using an up-to-date browser and still receiving this error code, there could be a problem with the host’s web server.

407 Proxy Authentication Required: The client must first authenticate itself with the proxy
This error indicates that the website owner is using a proxy server for added security and that you have to log into it before you are able to access the page you requested.

408 Request Timeout: The server timed out waiting for the request
This error means it took too long for the request for website information from your browser to be processed than the server was willing to wait. This could be due to a sudden drop in your internet connection or speed, or it could be an issue with the website’s server. This can usually be fixed by refreshing the page and trying again. You can check whether the problem is with you or the website by accessing dependable pages like Google and observing their load time. If they load ok, then the problem is probably due to the web server.

409 Conflict: Request could not be processed because of conflict in the request
In simple terms, this error means you tried to do something which the web server has previously been told should not be allowed. This creates a conflict for the server as it tries to fulfil your request and at the same time cannot. This should not normally occur with everyday web browsing.

410 Gone: Resource requested is no longer available and will not be available again
This error code means you’ve tried to access a page which either no longer exists or has been moved without a redirect. It is similar to a 404 Not Found message but deliberately put in place to let you know that the page won’t be reappearing again and that links to it should be removed.


500 Internal Server Error: A generic error message, given when an unexpected condition was encountered
This is a “one-size-fits-all” response when there has been a problem somewhere between the URL request by your browser and the response from the web server. The problem is with the web server itself and this error creates a more detailed log of the problem on the server for the administrator to take a look at. Because the problem is with the server, no more detail is given to the browser user about what went wrong.

501 Not Implemented: The server either does not recognize the request method, or it lacks the ability to fulfil the request
This error is a problem with the web server and typically occurs if the server is old and hasn’t been updated in a while. Specifically, it means that the browser sent a request that the web server couldn’t understand.

502 Bad Gateway: The server was acting as a gateway or proxy and received an invalid response
This occurs when a proxy server is being used and there is a problem in communication between the proxy and the web server. It could mean a fault with either machine, or that one of them has been programmed incorrectly. Rarely this can be a problem with your browser or your internet connection. Clear your browser’s cache and check to see if other websites are accessible. If you get this message with all websites, there might be a problem with your ISP.

503 Service Unavailable: The server is currently unavailable
This error means that the web server is currently down for maintenance or is being repaired. It is a message put up by the owner of the server to let you know that normal operation of the website will resume sometime in the near future.

504 Gateway Timeout: The server was acting as a gateway or proxy and did not receive a timely response from the upstream server
If you see this error message, it means that a proxy server is being used by the website. It results when the response from the web server to the proxy takes too long, causing a timeout. This is a problem with the website’s servers and needs to be dealt with by the host.


600 Invalid Request: The provided URL is not valid
This is similar to a 501 Not Implemented error, in that it means your browser sent the web server a request it was not expecting and is therefore not designed to respond to. This could mean you are trying to access a page that is not meant to be displayed or not meant to be accessed using a browser and therefore the web server was sent a command it did not recognise.


900 Checking Error: An unknown error occured, please contact technical support
This is an error code used only for KeepUsUp checks that is returned if there is a technical problem with a website that doesn’t fit any of the other error codes already mentioned. If you are given this code, please contact us immediately at support@keepusup.com to learn more and so that we can fix the issue.

901 Text Mismatch: Matching text or address cannot be found
This is another KeepUsUp-specific error code. You will get this result if our check finds that the webpage loads correctly, but elements on the page do not. There could be a variety of reasons for this error, and we will look more closely if this issue occurs to find out what the problem is.


If you encounter any of these error codes while accessing your site or just want to know more about what they mean as part of your site diagnosis, please feel free to contact us at support@keepusup.com or through our online support form.

KeepUsUp Support Team

Comments are closed.