What do these HTTP error codes mean?

At one point or another a website will get an http error code, whether it’s due to a mandatory website update or simple error within code. The key is to figure out a solution. Downtime is something the web design and hosting industry are continually fighting to keep to a minimum. There are some http codes that you may never encounter and others encounter frequently, like 404 or the dreaded 500.

The HTTP error codes listed here are consider client-error code. So, let’s dive in and understand these codes better.

400(Bad request)This error will appear when an error is found within the syntax. Think of it as B is requesting data from the server A, but A is missing so the data cannot to shown.

It could be simple as trying to view a webpage that your browser has an old cached version of it and when you viewed the website that old cache data is no longer found. So, clearing your cache and history could solve the 400 error
401(Authorization required)Each website needs to show that the owners of the domain/website are authorized to show the content. But before you can view that content they must be authorized on the server to make that information available.
402(Payment required)The domain has been reserved for future use and may have the option of taking digital payments.

This code does not appear a lot, if rarely, you may see this code if related to a Bitcoin website.
403(Forbidden)The page is not viewable whatsoever, the server has blocked any information from being viewed.
404(Not found)This is a very common error found around the internet. 404 is due to a post or page has been deleted, moved or renamed and the proper redirects have not been setup.
405(Method not allowed)Whenever you have a, for example, form on your website the typical way is to use a GET, but that data required needs to actually be a POST command. Therefore because a GET is the most commonly used function within forms the ability to bookmark, share, remain in browser is available through a GET.

But, if the form deals with confidential, sensitive info a POST would be better suited. So, if your using a GET on a form that's asking for sensitive information that could be the source for a 405.
406(Not acceptable)There may be a file that exists, but your browser does not understand the format to show the file.

Before you rush to contact your web developer check your browser settings to ensure that file type in enabled to view it.
407(Proxy authentication required)In order to view specific data on a website, you may be required to log in to view the data. If you don't have the necessary access then you would contact your web domain provider.
408(Request timeout)A request may have been made through the browser, but failed to process within the timeframe allotted on the server. Internet speeds or sluggish browser cache could have resulted in a 408 error appearing.
409(Conflict)Multiple file uploads of the same exact content can result in a 409 error.
410(Gone)The post or page that was once available to view no longer exists or the server does not want to show the page. The urls of the pages or posts should either be updated with redirects or Remove URL's in Webmaster tools.

411(Length required)This isn't a common error since it originates from the client server (browser). Although, if it does appear is due to the web server telling the browser the content length needs to be defined.
412(Precondition failed)The server does not meet one of the preconditions that the requester put on the request.
413(Request entity too large)The request is larger than the server is willing or able to process.
414(Request URI too large)The URI provided was too long for the server to process. Often the result of too much data being encoded as a query-string of a GET request, in which case it should be converted to a POST request.
415(Unsupported media type)The request entity has a media type which the server or resource does not support. For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format.
416(Request range not satisfiable)he server cannot meet the requirements of the Expect request-header field.
417(Expectation failed)The server cannot meet the requirements of the Expect request-header field.
422(Unprocessable entity)The resource that is being accessed is locked
423(Locked)Not part of the HTTP standard, but defined by Spring in the HttpStatus class to be used when a method failed. This status code is deprecated by Spring.
424(Failed dependency)The request failed due to failure of a previous request
500(Internal server error)This error has to do with the actual server, the browser doesn't know what the error is the web hosting company should be contacted if the error doesn't go away after a few refreshes.
501(Not Implemented)Error occurs when the browser (client) does not recognize the HTTP method. The http method should have: GET, OPTIONS, HEAD, POST, PUT, DELETE, TRACE and CONNECT. If this is incorrect the browser will throw up a 501 error
502(Bad gateway)When requesting to view a website, the request to view the website is hit with an invalid request. This doesn't mean that the website you want to view is down or the IP is incorrect, but rather the upstream and gateway don't agree on how to exchange data.

Try clearing your cache, history, cookies or reset your IP address and attempt to view the website.
503(Service unavailable)The website you are trying to view could be under maintenance, the web server is under maintenance for a small duration of time. Wait and come back again to the website in a few minutes.

504(Gateway timeout)The website you're trying to view either has stalled due to the server not responding back as fast as the browser wanted.
505(HTTP version not supported)The server that the website is hosted on will not accept the protocols that the browser has set. This could be something as simple as having an out-dated browser (eg. Chrome 20, but Chrome 41 is the current version).
506(Variant also negotiates)Due to an internal server error, not the browser. Web hosting company should be contacted.

507(Insufficient storage)A temporary error due the website's hosting storage limitation. The website owner should contact the hosting company to change the storage size.
510(Not extended)The web server does not support an extension that is attached to the HTTP request. To resolve this issue, contact your system administrator.