HTTP Status Codes - Part 3 of Chapter 3 from HTTP: The Definitive Guide

Status code	Reason phrase	Meaning
400	Bad Request	Used to tell the client that it has sent a malformed request.
401	Unauthorized	Returned along with appropriate headers that ask the client to authenticate itself before it can gain access to the resource. See Chapter 12 for more on authentication.
402	Payment Required	Currently this status code is not used, but it has been set aside for future use.
403	Forbidden	Used to indicate that the request was refused by the server. If the server wants to indicate why the request was denied, it can include an entity body describing the reason. However, this code usually is used when the server does not want to reveal the reason for the refusal.
404	Not Found	Used to indicate that the server cannot find the requested URL. Often, an entity is included for the client application to display to the user.
405	Method Not Allowed	Used when a request is made with a method that is not supported for the requested URL. The Allow header should be included in the response to tell the client what methods are allowed on the requested resource. See "Entity Headers" for more on the Allow header.
406	Not Acceptable	Clients can specify parameters about what types of entities they are willing to accept. This code is used when the server has no resource matching the URL that is acceptable for the client. Often, servers include headers that allow the client to figure out why the request could not be satisfied. See for more information.
407	Proxy Authentication Required	Like the 401 status code, but used for proxy servers that require authentication for a resource.
408	Request Timeout	If a client takes too long to complete its request, a server can send back this status code and close down the connection. The length of this timeout varies from server to server but generally is long enough to accommodate any legitimate request.
409	Conflict	Used to indicate some conflict that the request may be causing on a resource. Servers might send this code when they fear that a request could cause a conflict. The response should contain a body describing the conflict.
410	Gone	Similar to 404, except that the server once held the resource. Used mostly for web site maintenance, so a server's administrator can notify clients when a resource has been removed.
411	Length Required	Used when the server requires a Content-Length header in the request message. See "Content headers" for more on the Content-Length header.
412	Precondition Failed	Used if a client makes a conditional request and one of the conditions fails. Conditional requests occur when a client includes an Expect header. See Appendix C for more on the Expect header.
413	Request Entity Too Large	Used when a client sends an entity body that is larger than the server can or wants to process.
414	Request URI Too Long	Used when a client sends a request with a request URL that is larger than the server can or wants to process.
415	Unsupported Media Type	Used when a client sends an entity of a content type that the server does not understand or support.
416	Requested Range Not Satisfiable	Used when the request message requested a range of a given resource and that range either was invalid or could not be met.
417	Expectation Failed	Used when the request contained an expectation in the Expect request header that the server could not satisfy. See Appendix C for more on the Expect header. A proxy or other intermediary application can send this response code if it has unambiguous evidence that the origin server will generate a failed expectation for the request.

Status code

Reason phrase

Meaning

400

Bad Request

Used to tell the client that it has sent a malformed request.

401

Unauthorized

Returned along with appropriate headers that ask the client to authenticate itself before it can gain access to the resource. See Chapter 12 for more on authentication.

402

Payment Required

Currently this status code is not used, but it has been set aside for future use.

403

Forbidden

Used to indicate that the request was refused by the server. If the server wants to indicate why the request was denied, it can include an entity body describing the reason. However, this code usually is used when the server does not want to reveal the reason for the refusal.

404

Not Found

Used to indicate that the server cannot find the requested URL. Often, an entity is included for the client application to display to the user.

405

Method Not Allowed

Used when a request is made with a method that is not supported for the requested URL. The Allow header should be included in the response to tell the client what methods are allowed on the requested resource. See "Entity Headers" for more on the Allow header.

406

Not Acceptable

Clients can specify parameters about what types of entities they are willing to accept. This code is used when the server has no resource matching the URL that is acceptable for the client. Often, servers include headers that allow the client to figure out why the request could not be satisfied. See for more information.

407

Proxy Authentication Required

Like the 401 status code, but used for proxy servers that require authentication for a resource.

408

Request Timeout

If a client takes too long to complete its request, a server can send back this status code and close down the connection. The length of this timeout varies from server to server but generally is long enough to accommodate any legitimate request.

409

Conflict

Used to indicate some conflict that the request may be causing on a resource. Servers might send this code when they fear that a request could cause a conflict. The response should contain a body describing the conflict.

410

Gone

Similar to 404, except that the server once held the resource. Used mostly for web site maintenance, so a server's administrator can notify clients when a resource has been removed.

411

Length Required

Used when the server requires a Content-Length header in the request message. See "Content headers" for more on the Content-Length header.

412

Precondition Failed

Used if a client makes a conditional request and one of the conditions fails. Conditional requests occur when a client includes an Expect header. See Appendix C for more on the Expect header.

413

Request Entity Too Large

Used when a client sends an entity body that is larger than the server can or wants to process.

414

Request URI Too Long

Used when a client sends a request with a request URL that is larger than the server can or wants to process.

415

Unsupported Media Type

Used when a client sends an entity of a content type that the server does not understand or support.

416

Requested Range Not Satisfiable

Used when the request message requested a range of a given resource and that range either was invalid or could not be met.

417

Expectation Failed

Used when the request contained an expectation in the Expect request header that the server could not satisfy. See Appendix C for more on the Expect header.

A proxy or other intermediary application can send this response code if it has unambiguous evidence that the origin server will generate a failed expectation for the request.