Introduction To .Net Web API HTTP Codes

What is HTTP Code

HTTP Code is simply a numeric value used to exchange information between Server and Client. HTTP response status codes indicate whether a specific HTTP request has been successfully completed. Responses are grouped into five classes:

  1. Informational responses ( 100 – 199 )
  2. Successful responses ( 200 – 299 )
  3. Redirection messages ( 300 – 399 )
  4. Client error responses ( 400 – 499 )
  5. Server error responses ( 500 – 599 )

Information responses

100 Continue

Response indicates that the client should continue the request or ignore the response if the request is already finished.

101 Switching Protocols

Response to an Upgrade request header from the client and indicates the protocol the server is switching to.

102 Processing

Indicates that the server has received and is processing the request, but no response is available yet.

Successful responses

200 OK

Request succeeded. The result meaning of "success" depends on the HTTP method,

  • GET The resource has been fetched and transmitted in the message body.
  • HEAD The representation headers are included in the response without any message body.
  • PUT or POST The resource describing the result of the action is transmitted in the message body.
  • TRACE The message body contains the request message as received by the server.

201 Created

Create/POST Request succeeded, and a new resource was created as a result. This is typically the response sent after POST requests, or some PUT requests.

202 Accepted

Request has been received but not yet acted upon. It is noncommittal since there is no way in HTTP to later send an asynchronous response indicating the outcome of the request.

204 No Content

No content to send for this request, but the headers may be useful.

205 Reset Content

User agent to reset the document which sent this request.

206 Partial Content

Response code is used when the Range header is sent from the client to request only part of a resource.

Redirection messages

307 Temporary Redirect

Server Response to direct the client to get the requested resource at another URI with same method that was used in the prior request. This has the same semantics as the 302 Found HTTP response code, with the exception that the user agent must not change the HTTP method used: if a POST was used in the first request, a POST must 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 Permanently HTTP response code, with the exception that the user agent must not change the HTTP method used: if a POST was used in the first request, a POST must be used in the second request.

Client error responses

400 Bad Request

Server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

401 Unauthorized

Although the HTTP standard specifies "unauthorized", semantically this response means "unauthenticated". That is, the client must authenticate itself to get the requested response.

402 Payment Required

Response code is reserved for future use. The initial aim for creating this code was using it for digital payment systems, however this status code is used very rarely and no standard convention exists.

403 Forbidden

Client does not have access rights to the content; that is, it is unauthorized, so the server is refusing to give the requested resource. Unlike 401 Unauthorized, the client's identity is known to the server.

404 Not Found

Server can not find the requested resource. In the browser, this means the URL is not recognized. In an API, this can also mean that the endpoint is valid but the resource itself does not exist. Servers may also send this response instead of 403 Forbidden to hide the existence of a resource from an unauthorized client. This response code is probably the most well known due to its frequent occurrence on the web.

405 Method Not Allowed

Request method is known by the server but is not supported by the target resource. For example, an API may not allow calling DELETE to remove a resource.

406 Not Acceptable

Response is sent when the webserver, after performing server-driven content negotiation, doesn't find any content that conforms to the criteria given by the user agent.

407 Proxy Authentication Required

This is similar to 401 Unauthorized but authentication is needed to be done by a proxy.

408 Request Timeout

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.

Server error responses

500 Internal Server Error

Server has encountered a situation it does not know how to handle.

501 Not ImplementedRequest 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 GET and HEAD .

502 Bad Gateway

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

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 response 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

Error response is given when the server is acting as a gateway and cannot get a response in time.

In .net WebAPI we have a class called StatusCodes Class which has predefined constants to send as reply in web API responses.

Field Code
Status100Continue 100
Status101SwitchingProtocols 101
Status102Processing 102
Status200OK 200
Status201Created 201
Status202Accepted 202
Status203NonAuthoritative 203
Status204NoContent 204
Status205ResetContent 205
Status206PartialContent 206
Status207MultiStatus 207
Status208AlreadyReported 208
Status226IMUsed 226
Status300MultipleChoices 300
Status301MovedPermanently 301
Status302Found 302
Status303SeeOther 303
Status304NotModified 304
Status305UseProxy 305
Status306SwitchProxy 306
Status307TemporaryRedirect 307
Status308PermanentRedirect 308
Status400BadRequest 400
Status401Unauthorized 401
Status402PaymentRequired 402
Status403Forbidden 403
Status404NotFound 404
Status405MethodNotAllowed 405
Status406NotAcceptable 406
Status408RequestTimeout 408
Status409Conflict 409
Status410Gone 410
Status411LengthRequired 411
Status412PreconditionFailed 412
Status413PayloadTooLarge 413
Status413RequestEntityToo 413
Status414RequestUriTooLong 414
Status414UriTooLong 414
Status415UnsupportedMedia 415
Status416RangeNotSatisfiable 416
Status416RequestedRangeNot 416
Status417ExpectationFailed 417
Status418ImATeapot 418
Status419Authentication 419
Status421MisdirectedRequest 422
Status422UnprocessableEntity 422
Status423Locked 423
Status424FailedDependency 424
Status426UpgradeRequired 426
Status428Precondition 428
Status429TooManyRequests 429
Status431RequestHeaderFields 431
Status500InternalServerError 500
Status501NotImplemented 501
Status502BadGateway 502
Status503ServiceUnavailable 503
Status504GatewayTimeout 504
Status505HttpVersion 505
Status506VariantAlso 506
Status507InsufficientStorage 507
Status508LoopDetected 508
Status510NotExtended 510
Status511Network AuthenticationRequired 511


In Web API response it is very important to handle appropriate response codes to enhance the user experience on the website. This article gives an extensive list of Status codes that can be handled in the web API responses