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:
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.
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.
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.
Request succeeded and new resource has been created.
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.
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.
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.
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.
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.
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.
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.
Code sent when a request conflicts with current state of server.
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.
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.
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