Http Response Codes 4xx & Meanings

Hello friends, Today we are going to discuss about http response codes 4xx. In previous articles we have discussed about

Http status code 1xx

Http status code 2xx

Http status code 3xx

Note: http response codes 4xx are indication of Client Errors. ** is prefixed for most commonly used status codes.

So let’s start.

**400 Bad Request

The request could not be understood by the server due to incorrect syntax.

**401 Unauthorized

The request requires user authentication. The response MUST include a WWW-Authenticate header field containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field. If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials.

402 Payment Required

Reserved for future use. The original intention was that this code might be used as part of some form of digital cash or micro payment scheme, but that has not yet happened, and this code is not usually used. Google Developers API uses this status if a particular developer has exceeded the daily limit on requests.

**403 Forbidden

The server understood the request, but is refusing to fulfill it. Authorization will not help and the request SHOULD NOT be repeated. If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it SHOULD describe the reason for the refusal in the entity. If the server does not wish to make this information available to the client, the status code 404 (Not found) can be used instead.

**404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.

405 Method Not Allowed

The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource. For example, using GET on a form which requires data to be presented via POST, or using PUT on a read-only resource.

406 Not Acceptable

The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.

HTTP/1.1 servers are allowed to return responses which are not acceptable according to the accept headers sent in the request. In some cases, this may even be preferable to sending a 406 response. User agents are encouraged to inspect the headers of an incoming response to determine if it is acceptable.

407 Proxy Authentication Required

This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy. The proxy MUST return a Proxy-Authenticate header field containing a challenge applicable to the proxy for the requested resource. The client MAY repeat the request with a suitable Proxy-Authorization header field.

408 Request Timeout

The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.

**409 Conflict

The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response body SHOULD include enough information for the user to recognize the source of the conflict. Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.

Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the entity being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might use the 409 response to indicate that it can’t complete the request. In this case, the response entity would likely contain a list of the differences between the two versions in a format defined by the response Content-Type.

**410 Gone

The requested resource is no longer available at the server and no forwarding address is known. This condition is expected to be considered permanent. If the server does not know, or has no facility to determine, whether or not the condition is permanent, the status code 404 (Not Found) should be used instead.

The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource is intentionally unavailable.

411 Length Required

The server refuses to accept the request without a defined Content- Length. The client MAY repeat the request if it adds a valid Content-Length header field containing the length of the message-body in the request message.

412 Precondition Failed

The precondition given in one or more of the request-header fields evaluated as false when it was tested on the server.

413 Request Entity Too Large

The server is refusing to process a request because the request entity is larger than the server is willing or able to process. The server MAY close the connection to prevent the client from continuing the request.

414 Request-URI Too Long

The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information.

415 Unsupported Media Type

The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.

416 Requested Range Not Satisfying

A server SHOULD return a response with this status code if a request included a Range request-header field, and none of the range-specifier values in this field overlap the current extent of the selected resource, and the request did not include an If-Range request-header field

When this status code is returned for a byte-range request, the response SHOULD include a Content-Range entity-header field specifying the current length of the selected resource.

417 Expectation Failed

The expectation given in an Expect request-header field could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.

418 I’m a teapot (RFC 2324)

This code was defined in 1998 as one of the traditional IETF April Fools’ jokes, in RFC 2324, Hyper Text Coffee Pot Control Protocol, and is not expected to be implemented by actual HTTP servers. However, known implementations do exist. An Nginx HTTP server uses this code to simulate goto like behavior in its configuration.

Alex explained it pretty well here.

420 Enhance Your Calm (Twitter)

Returned by the Twitter Search and Trends API when the client is being rate limited and is sending too many requests.

422 not process able Entity (WebDAV)

The 422 (Unprocessable Entity) status code means the server understands the content type of the request entity, and the syntax of the request entity is correct but was unable to process the contained instructions.

For example, this error condition may occur if an XML request body contains well-formed (i.e., syntactically correct), but semantically erroneous, XML instructions.

423 Locked (WebDAV)

The 423 (Locked) status code means the source or destination resource of a method is locked. This response should contain an appropriate precondition or post condition code, such as ‘lock-token-submitted’ or ‘no-conflicting-lock’.

424 Failed Dependency (WebDAV)

The 424 (Failed Dependency) status code means that the method could not be performed on the resource because the requested action depended on another action and that action failed. 

425 Reserved for WebDAV

Defined in drafts of “WebDAV Advanced Collections Protocol”.

426 Upgrade Required

This is an indication to client that the client should switch to a different protocol such as TLS/1.0. This is required due to interoperability negotiation.

428 Precondition Required

The 428 status code indicates that the origin server requires the request to be conditional.

Its typical use is to avoid 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. By requiring requests to be conditional, the server can assure that clients are working with the correct copies.

429 Too Many Requests

The 429 status code indicates that the user has sent too many requests in a given amount of time (“rate limiting”).

The response representations SHOULD include details explaining the condition, and MAY include a Retry-After header indicating how long to wait before making a new request.

When a server is under attack or just receiving a very large number of requests from a single party, responding to each with a 429 status code will consume resources.

Therefore, servers are not required to use the 429 status code; when limiting resource usage, it may be more appropriate to just drop connections, or take other steps.

431 Request Header Fields Too Large

The 431 status code indicates that 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.

It can be used both when the set of request header fields in total are too large, and when a single header field is at fault. In the latter case, the response representation SHOULD specify which header field was too large.

Servers are not required to use the 431 status code; when under attack, it may be more appropriate to just drop connections, or take other steps.

444 No Response (Nginx)

An Nginx HTTP server extension. The server returns no information to the client and closes the connection (useful as a deterrent for malware).

449 Retry with (Microsoft)

A Microsoft extension. The request should be retried after performing the appropriate action.

450 Blocked by Windows Parental Controls (Microsoft)

A Microsoft extension. This error is given when Windows Parental Controls are turned on and are blocking access to the given webpage.

451 Unavailable For Legal Reasons

Intended to be used when resource access is denied for legal reasons, e.g. censorship or government-mandated blocked access.

499 Client Closed Request (Nginx)

An Nginx HTTP server extension. This code is introduced to log the case when the connection is closed by client while HTTP server is processing its request, making server unable to send the HTTP header back.


That’s it about http response codes 4xx. In upcoming articles we’ll discuss about next set of codes.