HTTP 狀態碼表明一個 HTTP 要求是否已經被完成。回應分為五種：資訊回應、成功回應、重定向、用戶端錯誤及伺服器端錯誤。
101 Switching Protocol
- 請求成功。成功的意義依照 HTTP 方法而定：
GET: 資源成功獲取並於 message body 內發送。
HEAD: entity 標頭已於 message body 內。
POST: 已傳送 message body 內的 resource describing the result of the action。
TRACE: 伺服器已接收到 message body 內含的請求訊息。
- 請求成功且新的資源成功被創建，這通常用於 PUT 請求後的回應。
- The request has been received but not yet acted upon. It is non-committal, meaning that there is no way in HTTP to later send an asynchronous response indicating the outcome of processing the request. It is intended for cases where another process or server handles the request, or for batch processing.
203 Non-Authoritative Information
- This response code means returned meta-information set is not exact set as available from the origin server, but collected from a local or a third party copy. Except this condition, 200 OK response should be preferred instead of this response.
204 No Content
- There is no content to send for this request, but the headers may be useful. The user-agent may update its cached headers for this resource with the new ones.
205 Reset Content
- This response code is sent after accomplishing request to tell user agent reset document view which sent this request.
206 Partial Content
- This response code is used because of range header sent by the client to separate download into multiple streams.
- A Multi-Status response conveys information about multiple resources in situations where multiple status codes might be appropriate.
- Used inside a DAV: propstat response element to avoid enumerating the internal members of multiple bindings to the same collection repeatedly.
226 IM Used(HTTP Delta encoding)
- The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.
300 Multiple Choice
- 請求擁有一個以上的回應。User-agent 或 user 應當從中選一。不過，並沒有標準的選擇方案。
301 Moved Permanently
- 此回應碼的意思是，請求資源的 URI 已被改變。有時候，會在回應內給予新的 URI。
- This response code means that URI of requested resource has been changed temporarily. New changes in the URI might be made in the future. Therefore, this same URI should be used by the client in future requests.
303 See Other
- Server sent this response to directing client to get requested resource to another URI with an GET request.
304 Not Modified
- This is used for caching purposes. It is telling to client that response has not been modified. So, client can continue to use same cached version of response.
305 Use Proxy
- Was defined in a previous version of the HTTP specification to indicate that a requested response must be accessed by a proxy. It has been deprecated due to security concerns regarding in-band configuration of a proxy.
- This response code is no longer used, it is just reserved currently. It was used in a previous version of the HTTP 1.1 specification.
307 Temporary Redirect
- Server sent this response to directing client to get requested resource to another URI with same method that used prior request. This has the same semantic than the
302 FoundHTTP response code, with the exception that the user agent must not change the HTTP method used: if a
POSTwas used in the first request, a
POSTmust be used in the second request.
308 Permanent Redirect
- This means that the resource is now permanently located at another URI, specified by the
Location:HTTP Response header. This has the same semantics as the
301 Moved PermanentlyHTTP response code, with the exception that the user agent must not change the HTTP method used: if a
POSTwas used in the first request, a
POSTmust be used in the second request.
400 Bad Request
- 需要授權以回應請求。它有點像 403，但這裡的授權，是有可能辦到的。
402 Payment Required
404 Not Found
- 伺服器找不到請求的資源。因為在 web 上它很常出現，這回應碼也許最為人所悉。
405 Method Not Allowed
406 Not Acceptable
- This response is sent when the web server, after performing server-driven content negotiation, doesn't find any content following the criteria given by the user agent.
407 Proxy Authentication Required
- This is similar to 401 but authentication is needed to be done by a proxy.
408 Request Timeout
- This response is sent on an idle connection by some servers, even without any previous request by the client. It means that the server would like to shut down this unused connection. This response is used much more since some browsers, like Chrome, Firefox 27+, or IE9, use HTTP pre-connection mechanisms to speed up surfing. Also note that some servers merely shut down the connection without sending this message.
- This response would be sent when a request conflict with current state of server.
- This response would be sent when requested content has been deleted from server.
411 Length Required
- Server rejected the request because the
Content-Lengthheader field is not defined and the server requires it.
412 Precondition Failed
- The client has indicated preconditions in its headers which the server does not meet.
413 Payload Too Large
- Request entity is larger than limits defined by server; the server might close the connection or return an
414 URI Too Long
- The URI requested by the client is longer than the server is willing to interpret.
415 Unsupported Media Type
- The media format of the requested data is not supported by the server, so the server is rejecting the request.
416 Requested Range Not Satisfiable
- The range specified by the
Rangeheader field in the request can't be fulfilled; it's possible that the range is outside the size of the target URI's data.
417 Expectation Failed
- This response code means the expectation indicated by the
Expectrequest header field can't be met by the server.
418 I'm a teapot
- The server refuses the attempt to brew coffee with a teapot.
421 Misdirected Request
- The request was directed at a server that is not able to produce a response. This can be sent by a server that is not configured to produce responses for the combination of scheme and authority that are included in the request URI.
422 Unprocessable Entity(WebDAV)
- The request was well-formed but was unable to be followed due to semantic errors.
- The resource that is being accessed is locked.
424 Failed Dependency(WebDAV)
- The request failed due to failure of a previous request.
426 Upgrade Required
- The server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol. The server sends an
Upgradeheader in a 426 response to indicate the required protocol(s).
428 Precondition Required
- The origin server requires the request to be conditional. Intended to prevent the 'lost update' problem, where a client GETs a resource's state, modifies it, and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.
429 Too Many Requests
- The user has sent too many requests in a given amount of time ("rate limiting").
431 Request Header Fields Too Large
- The server is unwilling to process the request because its header fields are too large. The request MAY be resubmitted after reducing the size of the request header fields.
451 Unavailable For Legal Reasons
500 Internal Server Error
501 Not Implemented
- The request method is not supported by the server and cannot be handled. The only methods that servers are required to support (and therefore that must not return this code) are
502 Bad Gateway
- This error response means that the server, while working as a gateway to get a response needed to handle the request, got an invalid response.
503 Service Unavailable
- The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded. Note that together with this response, a user-friendly page explaining the problem should be sent. This responses should be used for temporary conditions and the
Retry-After:HTTP header should, if possible, contain the estimated time before the recovery of the service. The webmaster must also take care about the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.
504 Gateway Timeout
- This error response is given when the server is acting as a gateway and cannot get a response in time.
505 HTTP Version Not Supported
- The HTTP version used in the request is not supported by the server.
506 Variant Also Negotiates
- The server has an internal configuration error: transparent content negotiation for the request results in a circular reference.
507 Insufficient Storage
- The server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself, and is therefore not a proper end point in the negotiation process.
508 Loop Detected(WebDAV)
- The server detected an infinite loop while processing the request.
510 Not Extended
- Further extensions to the request are required for the server to fulfill it.
511 Network Authentication Required
- The 511 status code indicates that the client needs to authenticate to gain network access.