Note: If you're actually seeing HTTP error codes greater than 415 and less than 500, they're bogus. Most likely your web access is going through Winproxy, which returns "HTTP" error codes such as 425... which actually appears to be borrowed from the FTP error codes, and is not legitimate in HTTP.

If you want standard codes, go complain to the perpetrators of Winproxy, OSitis (literally, an inflammation of the operating system).

Hey, looky: OSitis documented their WinPoxy error codes. Finally.

Extended HTTP Error Codes

Standard Codes

We're all familiar with 404, and perhaps 403... but have you ever wondered what the other HTTP error codes are?

Here, for your edification, is the list of RFC2068 (HTTP 1.1) client error (400-series) codes:

400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed
413 Request Entity Too Large
414 Request-URI Too Long
415 Unsupported Media Type

Extended Codes

In addition, several extended client error codes exist, though they are not widely used:

419 Assistance needed in delivering $45 Million (Forty-five Million US Dollars)
420 Server stoned
423 Insufficient Postage
424 Dog in Yard
425 Undeliverable as Addressed
433 Client Certificate Lacks HAZMAT Endorsement
447 Dropped by Accident in the Pacific Ocean
478 It's Not My Fault
746 Divergent Temporal Instability

NOTE: these extended error codes are bogus (just in case you hadn't figured that out already). RFC2068 does not in fact define 400-series error codes above 415. If you're getting an error 425, it's either (a) an FTP error, not HTTP, or (b) a bogus error code returned by a proxy which doesn't conform to the HTTP/1.1 standard.

For the authoritative reference, see