There are various client requests and error pages that can happen when someone is navigating a website. A brief list of them is listed below. Please correct or add something that is lacking or erroneous. 200 - Okay 201 - Created 202 - Accepted 203 - Non-Authorative Information 204 - No Content 205 - Reset Content 206 - Partial Content 400 - Bad Request 401 - Authorization Required 402 - Payment Required 403 - Forbidden 404 - Not Found 405 - Method Not Allowed 406 - Not Acceptable 407 - Proxy Authentication Required 408 - Request Timed Out 409 - Conflicting Request 410 - Gone 411 - Content Length Required 412 - Precondition Failed 413 - Request Entity Too Long 414 - Request URI Too Long 415 - Unsupported Media Type
There are some starting with 5xx as well (errors on server side). Just to fill in your list: 500 Internal Server Error 501 Not Implemented 502 Bad Gateway 503 Service Unavailable 504 Gateway Timeout 505 HTTP Version Not Supported Apache can also return codes starting with 3xx but those aren't errors, those are redirect response codes, such as: 300 Multiple Choices 301 Moved Permanently 302 Moved Temporarily 303 See Other 304 Not Modified 305 Use Proxy There are a lot more, but these are the most common response codes.