The Internet HTTP1.1 protocol specifies a whole set of errors that are recorded by most servers. The error codes are encoded into decimal ranges. For the full set of error codes please refer to RFC2616 for the authoritative explanation.

The status codes are returned to the client making the request (typically an Internet Browser) and also recorded in the server's log file.

100 to 199 Informational status codes, rarely used

200 to 299 Successful, only 200 frequently used

300 to 399 Warning - but the request may still be satisfiable

400 to 499 Client Error, the request was invalid in some way

500 to 599 Server Error, the server could not fulfil the (valid) request

Of all these possible errors you are only ever likely to see a handful when analyzing a server log file, these are shown in bold.

100 Continue The request is progressing normally

200 Success The request was successful. Hopefully the most frequent status code

201 Created A new resource has been created successfully on the server

202 Accepted Request accepted but not completed yet, it will continue asynchronously

203 Non Authoritative Request probably completed successfully but can't tell from original server

204 Empty Success : The requested completed successfully but the resource requested is empty (has zero length)

205 Reset The requested completed successfully but the client should clear down any cached information as it may now be invalid

206 Cancel The request was canceled before it could be fulfilled. Typically the user gave up waiting for data and went to another page. Some download accelerator programs produce this error as they submit multiple requests to download a file at the same time

300 Multiple Choice The request is ambiguous and needs clarification as to which resource was requested

301 Moved The resource has permanently moved elsewhere, the response indicates where it has gone to.

302 Found The resource has temporarily moved elsewhere, the response indicates where it is at present

303 Redirect A preferred alternative source should be used at present

304 Not modified The server has identified from the request information that the client's copy of the information is up-to-date and the requested information does not need to be sent again.

305 Use Proxy The request must be sent through the indicated proxy server

307 Temporary Redirect The resource has temporarily moved elsewhere, the response indicates where it is at present. Client should still use this URL.

400 Bad Request The request header was not understood

401 Unauthorised The client does not have access to this resource, authorization is needed

402 Payment Required Reserved for future use

403 Forbidden Access to a resource is not allowed. The most frequent case of this occurs when directory listing access is not allowed.

404 Not found The resource request was not found. This is the code returned for missing pages or graphics. Viruses will often attempt to access resources that do not exist, so the error does not necessarily represent a problem

405 Not Allowed The access method (GET, POST, HEAD) is not allowed on this resource

406 Not Acceptable None of the acceptable file types (as requested by client) are available for this resource

407 Proxy Authentication The client does not have access to this resource, proxy authorization is needed

408 Timeout The client did not send a request within the required time period

409 Conflict There is an internal conflict of access to the resource

410 Gone The requested resource used to be on the server but is no longer available. Any robot seeing this response should delete the reference from its information store.

411 Length Required The request requires the Content-Length HTTP request field to be specified

412 Precondition Failed The request's HTTP header specified conditions that can not be met

413 Request Too Large The URL is too long (possibly too many query strings)

414 URL Too Large The URL is too long (possibly too many query keyword/value pairs)

415 Unsupported Media The server does not support the resource type requested

416 Requested Range invalid The portion of the resource requested is not available or out of range

417 Expectation Failed The Expect specifier in the HTTP request header can not be met

500 Internal Server Error The server had some sort of internal error trying to fulfil the request. The client may see a partial page or error message. It's a fault in the server and happens all too frequently.

501 Not Implemented The request needs functionality not available on the server

502 Bad Gateway The response by an intermediary server was invalid. This may happen if there is a problem with the DNS routing tables.

503 Service unavailable Service temporarily unavailable - typically because it is currently overloaded.

504 Gateway Timeout The server did not respond back to the gateway within acceptable time period

505 Version not supported The request uses a version of HTTP that is not supported

100 to 199	Informational status codes, rarely used
200 to 299	Successful, only 200 frequently used
300 to 399	Warning - but the request may still be satisfiable
400 to 499	Client Error, the request was invalid in some way
500 to 599	Server Error, the server could not fulfil the (valid) request

100	Continue	The request is progressing normally
200	Success	The request was successful. Hopefully the most frequent status code
201	Created	A new resource has been created successfully on the server
202	Accepted	Request accepted but not completed yet, it will continue asynchronously
203	Non Authoritative	Request probably completed successfully but can't tell from original server
204	Empty	Success : The requested completed successfully but the resource requested is empty (has zero length)
205	Reset	The requested completed successfully but the client should clear down any cached information as it may now be invalid
206	Cancel	The request was canceled before it could be fulfilled. Typically the user gave up waiting for data and went to another page. Some download accelerator programs produce this error as they submit multiple requests to download a file at the same time
300	Multiple Choice	The request is ambiguous and needs clarification as to which resource was requested
301	Moved	The resource has permanently moved elsewhere, the response indicates where it has gone to.
302	Found	The resource has temporarily moved elsewhere, the response indicates where it is at present
303	Redirect	A preferred alternative source should be used at present
304	Not modified	The server has identified from the request information that the client's copy of the information is up-to-date and the requested information does not need to be sent again.
305	Use Proxy	The request must be sent through the indicated proxy server
307	Temporary Redirect	The resource has temporarily moved elsewhere, the response indicates where it is at present. Client should still use this URL.
400	Bad Request	The request header was not understood
401	Unauthorised	The client does not have access to this resource, authorization is needed
402	Payment Required	Reserved for future use
403	Forbidden	Access to a resource is not allowed. The most frequent case of this occurs when directory listing access is not allowed.
404	Not found	The resource request was not found. This is the code returned for missing pages or graphics. Viruses will often attempt to access resources that do not exist, so the error does not necessarily represent a problem
405	Not Allowed	The access method (GET, POST, HEAD) is not allowed on this resource
406	Not Acceptable	None of the acceptable file types (as requested by client) are available for this resource
407	Proxy Authentication	The client does not have access to this resource, proxy authorization is needed
408	Timeout	The client did not send a request within the required time period
409	Conflict	There is an internal conflict of access to the resource
410	Gone	The requested resource used to be on the server but is no longer available. Any robot seeing this response should delete the reference from its information store.
411	Length Required	The request requires the Content-Length HTTP request field to be specified
412	Precondition Failed	The request's HTTP header specified conditions that can not be met
413	Request Too Large	The URL is too long (possibly too many query strings)
414	URL Too Large	The URL is too long (possibly too many query keyword/value pairs)
415	Unsupported Media	The server does not support the resource type requested
416	Requested Range invalid	The portion of the resource requested is not available or out of range
417	Expectation Failed	The Expect specifier in the HTTP request header can not be met
500	Internal Server Error	The server had some sort of internal error trying to fulfil the request. The client may see a partial page or error message. It's a fault in the server and happens all too frequently.
501	Not Implemented	The request needs functionality not available on the server
502	Bad Gateway	The response by an intermediary server was invalid. This may happen if there is a problem with the DNS routing tables.
503	Service unavailable	Service temporarily unavailable - typically because it is currently overloaded.
504	Gateway Timeout	The server did not respond back to the gateway within acceptable time period
505	Version not supported	The request uses a version of HTTP that is not supported