https://en.wikipedia.org/wiki/List_of_HTTP_status_codes
摘抄其中重點的部分

1xx Informational responses

2xx Success

This class of status codes indicates the action requested by the client was received, understood, accepted, and processed successfully.[2]

200 OK

Standard response for successful HTTP requests. The actual response will depend on the request method used. In a GET request, the response will contain an entity corresponding to the requested resource. In a POST request, the response will contain an entity describing or containing the result of the action.[7]

201 Created

The request has been fulfilled, resulting in the creation of a new resource.[8]

202 Accepted

The request has been accepted for processing, but the processing has not been completed. The request might or might not be eventually acted upon, and may be disallowed when processing occurs

3xx Redirection

This class of status code indicates the client must take additional action to complete the request. Many of these status codes are used in URL redirection.[2]

A user agent may carry out the additional action with no user interaction only if the method used in the second request is GET or HEAD. A user agent may automatically redirect a request. A user agent should detect and intervene to prevent cyclical redirects.[18]

300 Multiple Choices

Indicates multiple options for the resource from which the client may choose (via agent-driven content negotiation). For example, this code could be used to present multiple video format options, to list files with different filename extensions, or to suggest word-sense disambiguation.[19]

301 Moved Permanently

This and all future requests should be directed to the given URI.[20]

305 Use Proxy (since HTTP/1.1)

The requested resource is available only through a proxy, the address for which is provided in the response. Many HTTP clients (such as Mozilla[26] and Internet Explorer) do not correctly handle responses with this status code, primarily for security reasons.[27]

307 Temporary Redirect (since HTTP/1.1)

In this case, the request should be repeated with another URI; however, future requests should still use the original URI. In contrast to how 302 was historically implemented, the request method is not allowed to be changed when reissuing the original request. For example, a POST request should be repeated using another POST request.[29]

308 Permanent Redirect (RFC 7538)

The request and all future requests should be repeated using another URI. 307 and 308 parallel the behaviors of 302 and 301, but do not allow the HTTP method to change. So, for example, submitting a form to a permanently redirected resource may continue smoothly.[30]

4xx Client errors[edit]

The 4xx class of status codes is intended for situations in which the client seems to have erred. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents should display any included entity to the user.[31]

400 Bad Request

The server cannot or will not process the request due to an apparent client error (e.g., malformed request syntax, too large size, invalid request message framing, or deceptive request routing).[32]

401 Unauthorized (RFC 7235)

Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. See Basic access authentication and Digest access authentication.[33] ####401 semantically means "unauthenticated",[34] i.e. the user does not have the necessary credentials.
Note: Some sites issue HTTP 401 when an IP address is banned from the website (usually the website domain) and that specific address is refused permission to access a website.

403 Forbidden

The request was valid, but the server is refusing action. The user might not have the necessary permissions for a resource.

404 Not Found

The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.[36]

405 Method Not Allowed

A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.

408 Request Time-out

5xx Server error[edit]

The server failed to fulfill an apparently valid request.[55]

Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has encountered an error or is otherwise incapable of performing the request. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents should display any included entity to the user. These response codes are applicable to any request method.[56]

500 Internal Server Error

A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.[57]

501 Not Implemented

The server either does not recognize the request method, or it lacks the ability to fulfill the request. Usually this implies future availability (e.g., a new feature of a web-service API).[58]

502 Bad Gateway

The server was acting as a gateway or proxy and received an invalid response from the upstream server.[59]

503 Service Unavailable

The server is currently unavailable (because it is overloaded or down for maintenance). Generally, this is a temporary state.[60]

504 Gateway Time-out

The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.[61]

505 HTTP Version Not Supported

The server does not support the HTTP protocol version used in the request.[62]