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 http://www.ietf.org/rfc/rfc2068.txt.