HTTP Response Codes

HyperText Transfer Protocol (HTTP) is the language of website-to-website/server communication, and as such has created a series of “responses” that websites can issue servers or other websites. These commands are referred to as response codes that can indicate success, information, failures, or redirects. Search Engines gather response code information through their crawlers to create index libraries. Response codes have a significant impact on SEO as a result.

Here’s a list of all the possible Response Codes and their association:

Information Responses

100 Continue

Code indicates OK transmission and should continue with request or ignore if completed.

101 Switching Protocol

Code responds to an Upgrade request header by the client and indicates the protocol the server is switching too.

102 Processing

Code indicates the server has received and is processing the request but no response is yet available.

103 Early Hints

Code associated with Link header, and allows client to begin preloading resources while the server prepares a response.

Succesful Responses

200 OK

Request has succeeded

Success depends on HTTP method:

  • GET – Resources have been fetched and is transmitted into message body.
  • HEAD – Entity headers are in message body.
  • PUT / POST – Resource describing the result of the action is transmitted into message body.
  • TRACE – Message body contains the request messages received by server.
201 Created

Request succeeded and new resource has been created.

202 Accepted

Request has been received but not processed or commissioned. Often occurs when different servers handle Requests and Processing.

203 Non-Authoritative Information

Returned meta-information is not exactly from the origin server.

204 No Content

No content to send for this request.

205 Reset Content

Code sent after request is completed to inform client to reset document view.

206 Partial Content

Code is sent from a client including a range header to separate download into multiple streams.

207 Multi-status

Conveys information about multiple resources.

208 Multi-stats (WEBDAV)

Propstat response element to avoid enumerating the internal resources of multiple bindings of the same collection.

226 IM Used

Server has completed a GET request and the response is a representation of the result of one or more instance manipulations applied to the current instance.

Redirection Responses

300 Multiple Choice

The request has more than one possible response, the client should choose one.

301 Moved Permanently

URI of requested resource has been changed permanently. New URI sent in response for redirection.

302 Found

URI of requested resource has been changed temporarily. New changes can be made in the future.

303 See Other

Server response to direct client to retrieve the requested resource at another URI with a GET request.

304 Not Modified

Used for caching purposes. Response has not been modified so cached version can be used.

305 Use Proxy

Retracted in newer HTML due to security concerns. No longer in use.

306 Unused

No longer in use.

307 Temporary Redirect

Same functional purpose as 302 Found however client must not change HTTP method used.

308 Permanent Redirect

Same functional purpose as 301 Moved Permanently however client must not change HTTP method used.

Client Error Responses

400 Bad Request

Could not understand request due to invalid syntax.

401 Unauthorised

Response indicates lack of authentication, client must go authenticate itself. Server does not recognise client identity.

402 Payment Required

Response code is yet to be implemented in HTTP.

403 Forbidden

Client does not have access to content. Server recognises client identity but is rejected.

404 Not Found

Server could not find requested resource.

405 Method Not Allowed

Request method is known, but has been disabled and cannot be used to retrieve resource.

406 Not Acceptable

Response sent by the web server after completing server-driven content negotiation, where no content follows the request of the client.

407 Proxy Authentication Required

Authentication needed to be done through proxy. Similar to 401 Unauthorised error.

408 Request Timeout

Response is sent on an idle connection between servers without client requests.

409 Conflict

Code sent when a request conflicts with current state of server.

410 Gone

Response sent when requested content has been permanently removed from server with no forwarding URI.

411 Length Required

Rejected request because Content-Length header field is not defined.

412 Precondition Failed

Client specifies preconditions in headers which server does not satisfy.

413 Payload Too Large

Request entity is larger than limits of the server.

414 URI Too Long

Client URI requested is too long for server to process.

415 Unsupported Media Type

Media format requested by client is not supported by server.

416 Request Range Not Satisfiable

Range specified by client Range header can’t be satisfied.

417 Expectation Failed

Expect request header cannot be met by server.

421 Misdirect Request

Request was directed toward a server not able to produce a response.

422 Unprocessable Entity

Request was well-formed but could not be followed due to semantic errors.

423 Locked

Resource is locked.

425 Too Early

Server is unwilling to process a request that may be replayed.

426 Upgrade Required

Server refuses to perform request under current protocol, but will do so after client upgrades to a newer protocol.

428 Precondition Required

Origin server requires the request to be conditional to prevent GET retrieval, modification, and PUT.

429 Too Many Requests

Client has sent too many requests in a specified period of time.

431 Request Header Size Too Large

Server is unwilling to process because header fields are too large.

451 Unavailable For Legal Reasons

Client requests an illegal resource.

Server Error Responses

500 Internal Server Error

A response code for general, unaccounted for errors.

501 Not Implemented

Request method is not supported by the server.

502 Bad Gateway

The server requested, as a gateway, a resource that was required to handle the request and received an invalid response.

503 Service Unavailable

Server is not ready to handle the request. Often due to server maintenance or down-time.

504 Gateway Timeout

Server acting as a gateway cannot get a response within a specified time.

505 HTTP Version Not Supported

HTTP used by client is not supported by server.

506 Variant Also Negotiates

Transparent content negotiation results in a circular reference.

507 Insufficient Storage

Resource requested is configured to engage in transparent content negotiation itself. Therefore cannot be an end-point in negotiation process.

508 Loop Detected

An infinite loop was encountered when fulfilling request.

510 Not Extended

Further extensions are required by server in order to fulfil request.

511 Network Authentication Required

Authentication of client needed to access network.

HTTP Response Code Penalties And SEO | SEOSPIDRE
Which HTTP Response Codes are most penalised, and which are encouraged for SEO | Technical SEO at SEOSPIDRE

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