101 Switching Protocols
Action completed successfully
Success following a POST command
The request has been accepted for processing, but the processing has not been completed.
203 Partial Information
Response to a GET command, indicates that the returned meta information is from a private overlaid web.
204 No Content
Server has received the request but there is no information to send back.
205 Reset Content
206 Partial Content
The requested file was partially sent. Usually caused by stopping or refreshing a web page.
300 Multiple Choices
301 Moved Permanently
Requested a directory instead of a specific file. The web server added the filename index.html, index.htm, home.html, or home.htm to the URL.
302 Moved Temporarily
303 See Other
304 Not Modified
The cached version of the requested file is the same as the file to be sent.
305 Use Proxy
400 Bad Request
The request had bad syntax or was impossible to be satisified.
This error indicates that the user’s request contains incorrect syntax.
User failed to provide a valid user name / password required for access to file / directory.
This error indicates that the requested file requires authentication (a username and password).
402 Payment Required
The request does not specify the file name. Or the directory or the file does not have the permission that allows the pages to be viewed from the web.
This error indicates that the server will not allow the visitor to access the requested file. If a visitor receives this code unexpectedly, you should check the file’s permission settings, or check whether the file has been protected.
404 Not Found
The requested file was not found.
This error indicates that the server could not find the file that the visitor requested. This commonly occurs when a URL is mistyped.
These errors are caused by the server being unable to fulfill an apparently valid request from a visitor. Often, you will need the help of a server administrator to investigate them.
It is also important to consider that quite often, a chain of servers is handling an HTTP request, so that it may not be your server that is returning the error.
500 Internal Server Error
This error indicates that the server has encountered an unexpected condition. This often occurs when an application request cannot be fulfilled due to the application being configured incorrectly on the server.
501 Not Implemented
This error indicates that the HTTP method sent by the client is not supported by the server. This is most often caused by the server being out of date. It is a very rare error and generally requires that the web server be updated.
502 Bad Gateway
This error is usually due to improperly configured proxy servers. However, the problem may also arise when there is poor IP communication between back—end computers, when the client’s server is overloaded, or when a firewall is functioning improperly.
The first step in resolving the issue is to clear the client’s cache. This action should result in a different proxy being used to resolve the web server’s content.
503 Service Unavailable
This error occurs when the server is unable to handle requests due to a temporary overload or due to the server being temporarily closed for maintenance. The error indicates that the server will only temporarily be down. It is possible to receive other errors in place of 503.
Contact the server administrator if this problem persists.
504 Gateway Timeout
This error occurs when a server somewhere along the chain does not receive a timely response from a server further up the chain. The problem is caused entirely by slow communication between upstream computers.
To resolve this issue, contact the system administrator.
505 HTTP Version Not Supported
This error occurs when the server refuses to support the HTTP protocol that has been specified by the client computer. This can be caused by the protocol not being specified properly by the client computer; for example, if an invalid version number has been specified.
506 Variant Also Negotiates
This error indicates that the server is not properly configured. Contact the system administrator to resolve this issue.
507 Insufficient Storage
This error indicates that the server is out of free memory. This is most likely to occur when an application that is being requested cannot allocate the necessary system resources to run.
To resolve the issue, the server’s hard disk may need to be cleaned of any unnecessary documents to free up more hard disk space, its memory may need to be expanded, or it may simply need to be restarted.
Contact the system administrator for more information regarding this error message.
509 Bandwidth Limit Exceeded
This error occurs when the bandwidth limit imposed by the system administrator has been reached. The only fix for this issue is to wait until the limit is reset in the following cycle.
Consult the system administrator for information about acquiring more bandwidth.
510 Not Extended
This error occurs when an extension attached to the HTTP request is not supported by the web server.
To resolve the issue, you may need to update the server. Consult the system administrator for more information
Most common error codes
HTTP error 401 (unauthorized)
This error happens when a website visitor tries to access a restricted web page but isn’t authorized to do so, usually because of a failed login attempt.
HTTP error 400 (bad request)
This is basically an error message from the web server telling you that the application you are using (e.g. your web browser) accessed it incorrectly or that the request was somehow corrupted on the way.
HTTP error 403 (forbidden)
This error is similar to the 401 error, but note the difference between unauthorized and forbidden. In this case no login opportunity was available. This can for example happen if you try to access a (forbidden) directory on a website.
HTTP error 404 (not found)
Most people are bound to recognize this one. A 404 error happens when you try to access a resource on a web server (usually a web page) that doesn’t exist. Some reasons for this happening can for example be a broken link, a mistyped URL, or that the webmaster has moved the requested page somewhere else (or deleted it). To counter the ill effect of broken links, some websites set up custom pages for them (and some of those are really cool).
HTTP error 500 (internal server error)
The description of this error pretty much says it all. It’s a general-purpose error message for when a web server encounters some form of internal error. For example, the web server could be overloaded and therefore unable to handle requests properly.