{{Short description|none}} {{pp-protect|small=yes}} {{Use American English|date=July 2025}} {{Use mdy dates|date=July 2025}} {{HTTP}}
This article lists standard and notable non-standard HTTP response status codes. Standardized codes are defined by IETF as documented in Request for Comments (RFC) publications and maintained by the IANA.<ref name="iana_status_codes">{{cite web|url=https://www.iana.org/assignments/http-status-codes/|title=Hypertext Transfer Protocol (HTTP) Status Code Registry|publisher=Iana.org|access-date=January 8, 2015|archive-url=https://web.archive.org/web/20111211100506/https://www.iana.org/assignments/http-status-codes|archive-date=December 11, 2011|url-status=live}}</ref> Other, non-standard values are used by various servers. The descriptive text after the numeric code {{endash}} the ''reason phrase'' {{endash}} is shown here with typical value, but in practice, can be different or omitted.
==Standard codes== Status codes defined by IETF are listed below. Emphasized terms {{em |must}}, {{em |must not}} and {{em |should}} are interpretation guidelines as given by {{IETF RFC|2119}}.
===1xx informational response=== An informational response indicates that the request was received and understood and is being processed. It alerts the client to wait for a final response. The message does not contain a body. As the HTTP/1.0 standard did not define any 1xx status codes, servers {{em|must not}} send a 1xx response to an HTTP/1.0 compliant client except under experimental conditions.
;{{anchor|100}}100 Continue : The server has received the request headers and the client should proceed to send the request body (in the case of a request for which a body needs to be sent, such as a POST request). Sending a large request body to a server after a request has been rejected for inappropriate headers would be inefficient. To have a server check the request's headers, a client must send <code>Expect: 100-continue</code> as a header in its initial request and receive a <code>100 Continue</code> status code in response before sending the body. If the client receives an error code such as 403 (Forbidden) or 405 (Method Not Allowed) then it should not send the request's body. The response <code>417 Expectation Failed</code> indicates that the request should be repeated without the <code>Expect</code> header as it indicates that the server does not support expectations (this is the case, for example, of HTTP/1.0 servers).{{Ref RFC|9110|rsection=10.1.1}} ;{{anchor|101}}101 Switching Protocols : The requester has asked the server to switch protocols and the server has agreed to do so. ;{{anchor|102}}102 Processing (WebDAV; RFC 2518) : A WebDAV request may contain many sub-requests involving file operations, requiring a long time to complete the request. This code indicates that the server has received and is processing the request, but no response is available yet.{{Ref RFC|2518}} This prevents the client from timing out and assuming the request was lost. The status code is deprecated.<ref>{{cite web |title=102 Processing – HTTP MDN |date=July 25, 2023 |url=https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/102 |language=en-US}} 102 status code is deprecated</ref> ;{{anchor|103}}103 Early Hints (RFC 8297) :Used to return some response headers before final HTTP message.{{Ref RFC|8297}}
===2xx success=== A success status indicates that the action requested by the client was received, understood, and accepted.<ref name="iana_status_codes" />
;{{anchor|200}}200 OK : Standard response for successful HTTP requests. The actual response will depend on the request method used. In a GET request, the response will contain an entity corresponding to the requested resource. In a POST request, the response will contain an entity describing or containing the result of the action. ;{{anchor|201}}201 Created : The request has been fulfilled, resulting in the creation of a new resource.<ref>{{cite web|last1=Stewart|first1=Mark|last2=djna|title=Create request with POST, which response codes 200 or 201 and content|url=https://stackoverflow.com/questions/1860645/create-request-with-post-which-response-codes-200-or-201-and-content|website=Stack Overflow|access-date=16 October 2015|archive-url=https://web.archive.org/web/20161011010658/https://stackoverflow.com/questions/1860645/create-request-with-post-which-response-codes-200-or-201-and-content|archive-date=October 11, 2016|url-status=live}}</ref> ;{{anchor|202}}202 Accepted : The request has been accepted for processing, but the processing has not been completed. The request might or might not be eventually acted upon, and may be disallowed when processing occurs. ;{{anchor|203}}203 Non-Authoritative Information (since HTTP/1.1) : The server is a transforming proxy (e.g. a {{em|Web accelerator}}) that received a 200 OK from its origin, but is returning a modified version of the origin's response.{{Ref RFC|9110|rsection=15.3.4}}{{Ref RFC|9110|rsection=7.7}} ;{{anchor|204}}204 No Content : The server successfully processed the request, and is not returning any content. ;{{anchor|205}}205 Reset Content : The server successfully processed the request, asks that the requester reset its document view, and is not returning any content. ;{{anchor|206}}206 Partial Content : The server is delivering only part of the resource (byte serving) due to a range header sent by the client. The range header is used by HTTP clients to enable resuming of interrupted downloads, or split a download into multiple simultaneous streams. ;{{anchor|207}}207 Multi-Status (WebDAV; RFC 4918) : The message body that follows is by default an XML message and can contain a number of separate response codes, depending on how many sub-requests were made.{{Ref RFC|4918}} ;{{anchor|208}}208 Already Reported (WebDAV; RFC 5842) : The members of a DAV binding have already been enumerated in a preceding part of the (multistatus) response, and are not being included again. ;{{anchor|226}}226 IM Used (RFC 3229) : The server has fulfilled a request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.{{Ref RFC|3229}}
===3xx redirection=== A 3xx status indicates that the client must take additional action, generally URL redirection, to complete the request.<ref name="iana_status_codes" /> A user agent may carry out the additional action with no user interaction if the method used in the additional request is GET or HEAD. A user agent should prevent cyclical redirects.{{Ref RFC|9110|rsection=15.4}}
;{{anchor|300}}300 Multiple Choices : Indicates multiple options for the resource from which the client may choose (via agent-driven content negotiation). For example, this code could be used to present multiple video format options, to list files with different filename extensions, or to suggest word-sense disambiguation. ;{{anchor|301}}301 Moved Permanently : The link target was moved such that the request and future similar requests should be redirected to the given URI. If a client has link-editing capabilities, it should update references to the request URL. The response is cacheable unless indicated otherwise. Except for a GET request, the body should contain a hyperlink to the new URL(s). Except for a GET or HEAD request, the client must ask the user before redirecting.<ref name="RFC2616-301">{{cite ietf |last1=Fielding|display-authors=etal |title=10.3.2 301 Moved Permanently |rfc=2616 |page=61 |publisher=IETF |date=June 1999 |section=10.3.2}}</ref>{{pb}}This code is considered best practice for upgrading users from HTTP to HTTPS. Both Bing and Google recommend using this code to change the URL of a page as it is shown in search engine results, providing that URL will permanently change and is not due to be changed again any time soon.<ref name=":0">{{cite web |title=Site Move Tool |website=Bing Webmaster Help & How-to |url=https://www.bing.com/webmaster/help/how-to-use-the-site-move-tool-bb8f5112}}</ref><ref>{{cite web |title=301 redirects |website= Google Webmaster Tools Help |url=https://support.google.com/webmasters/bin/answer.py?hl=en&answer=93633}}</ref> ;{{anchor|302}}302 Found : Indicates that the resource is accessible via an alternate URL indicated in the Location header field. The HTTP/1.0 specification (which used reason phrase "Moved Temporarily") required the client to redirect with the same method,{{Ref RFC|1945}} but popular browsers instead changed the request to GET.<ref>{{cite web |last=Lawrence |first=Eric |url=http://blogs.msdn.com/b/ieinternals/archive/2011/08/19/understanding-the-impact-of-redirect-response-status-codes-on-http-methods-like-head-get-post-and-delete.aspx |work=EricLaw's IEInternals blog |access-date=2011-08-20 |title=HTTP Methods and Redirect Status Codes}}</ref> For this reason, HTTP/1.1 ({{IETF RFC|2616|link=no}}) added two status codes: 303 which requires changing the request to a GET and 307 which preserves the original request type. Despite the greater clarity provided by this disambiguation, the 302 code is still used in web frameworks to preserve compatibility with browsers that do not support HTTP/1.1.<ref>{{cite web|url=https://docs.djangoproject.com/en/dev/ref/request-response/#django.http.HttpResponseRedirect |title=Request and response objects | Django documentation | Django |publisher=Docs.djangoproject.com |access-date=2014-06-23}}</ref>{{Ref RFC|9110|rsection=15.4}} As a consequence, {{IETF RFC|7231|link=no}} (the update of {{IETF RFC|2616|link=no}}) changes the definition to allow user agents to rewrite POST to GET.<ref>{{cite web|last1=Fielding |first1=Roy T. |last2=Reschke |first2=Julian |url=https://tools.ietf.org/html/rfc7231#section-6.4.3 |title=Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content |date=June 2014 |publisher=Tools.ietf.org |access-date=2019-01-05}}</ref> ;{{anchor|303}}303 See Other (since HTTP/1.1) : If a server responds to a POST or other non-idempotent request with this code and a location header field, the client is expected to issue a GET request to the specified location. To trigger a request to the target resource using the same method, the server responds with 307 instead. : Use of this code has been proposed<ref name="IDREF">{{cite journal|lang=en|first1=Paolo|last1=Bouquet|first2=Heiko|last2=Stoermer|first3=Massimiliano|last3=Vignolo|date=12 January 2011|title=Web of Data and Web of Entities: Identity and Reference in Interlinked Data in the Semantic Web|work=Philosophy & Technology|volume=25|pages=5–26|publisher=Springer Nature|issn=2210-5441|doi=10.1007/s13347-010-0011-6}}</ref> as one way of responding to a request for a URI that identifies a real-world object according to Semantic Web theory (the other being the use of ''hash URIs'').<ref>{{cite journal|lang=en|year=2011|last1=Halpin|first1=Harry|last2=Presutti|first2=Valentina|title=The identity of resources on the Web: An ontology for Web architecture|work=Applied Ontology|issn=1875-8533|publisher=IOS Press|volume=6|issue=3|pages=263–293|doi=10.3233/AO-2011-0095}}</ref><ref name="IDREF"/> For example, if <code><nowiki>http://www.example.com/id/alice</nowiki>{{Cbignore}}</code> identifies a person, Alice, then it would be inappropriate for a server to respond to a GET request with 200 OK, as the server could not deliver Alice herself. Instead, the server would respond with 303 to redirect to a URI that provides a description of the person Alice.<ref name="IDREF"/> : Sometimes, this code is used when providing an HTTP-based web API that needs to respond to the caller immediately, but continue executing asynchronously, such as a long-lived image conversion. The web API provides a status check URI that allows the client to check on the operation's status. When complete, the response may contain this status code and a redirect URI to the final result.<ref>{{cite book|title=RESTful Web Services Cookbook|first1=Subbu|last1=Allamaraju|first2=Subrahmanyam|last2=Allamaraju|date=March 2010|publisher=O'Reilly Media|isbn=9780596801687}}</ref> ;{{anchor|304}}304 Not Modified : Indicates that the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match. In such case, there is no need to retransmit the resource since the client still has a previously-downloaded copy. ;{{anchor|305}}305 Use Proxy (since HTTP/1.1) :The requested resource is available only through a proxy, the address for which is provided in the response. For security reasons, many HTTP clients (such as Mozilla Firefox and Internet Explorer) do not obey this status code.<ref>{{cite web |url=https://bugzilla.mozilla.org/show_bug.cgi?id=187996#c13 |title=Mozilla Bugzilla Bug 187996: Strange behavior on 305 redirect, comment 13 |date=March 3, 2003 |access-date=May 21, 2009 |archive-url=https://web.archive.org/web/20140421051946/https://bugzilla.mozilla.org/show_bug.cgi?id=187996#c13 |archive-date=April 21, 2014 |url-status=dead}}</ref> ;{{anchor|306}}306 Switch Proxy : No longer used. Originally meant "Subsequent requests should use the specified proxy." ;{{anchor|307}}307 Temporary Redirect (since HTTP/1.1) : In this case, the request should be repeated with another URI; however, future requests should still use the original URI. In contrast to how 302 was historically implemented, the request method is not allowed to be changed when reissuing the original request. For example, a POST request should be repeated using another POST request. ;{{anchor|308}}308 Permanent Redirect : This and all future requests should be directed to the given URI. 308 parallels the behavior of 301, but {{em|does not allow the HTTP method to change}}. So, for example, submitting a form to a permanently redirected resource may continue smoothly.
===<span class="anchor" id="client errors"></span><span class="anchor" id="4xx client errors"></span>4xx client error=== alt=A The Wikimedia 404 message|thumb|404 error on Wikimedia A 4xx status code is for situations in which an error seems to have been caused by the client. Except when responding to a HEAD request, the server {{em |should}} include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents {{em|should}} display any included entity to the user. ;{{anchor|400}}400 Bad Request : The server cannot or will not process the request due to an apparent client error (e.g., malformed request syntax, size too large, invalid request message framing, or deceptive request routing). ;{{anchor|401}}401 Unauthorized : Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. See Basic access authentication and Digest access authentication. 401 semantically means "unauthenticated", the user does not have valid authentication credentials for the target resource. ;{{anchor|402}}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 micropayment scheme, as proposed, for example, by GNU Taler,<ref>{{Cite web|url=https://docs.taler.net/merchant/frontend/php/html/tutorial.html#Headers-for-HTTP-402|title=The GNU Taler tutorial for PHP Web shop developers 0.4.0|website=docs.taler.net|access-date=2017-10-29|archive-url=https://web.archive.org/web/20171108142249/https://docs.taler.net/merchant/frontend/php/html/tutorial.html#Headers-for-HTTP-402|archive-date=November 8, 2017|url-status=dead}}</ref> but that has not yet happened, and this code is not widely used. Google Developers API uses this status if a particular developer has exceeded the daily limit on requests.<ref>{{cite web |url=https://developers.google.com/doubleclick-search/v2/standard-error-responses#PAYMENT_REQUIRED |title=Google API Standard Error Responses |year=2016 |access-date=June 21, 2017 |archive-url=https://web.archive.org/web/20170525005121/https://developers.google.com/doubleclick-search/v2/standard-error-responses#PAYMENT_REQUIRED |archive-date=May 25, 2017 |url-status=dead}}</ref> Sipgate uses this code if an account does not have sufficient funds to start a call.<ref>{{cite web|url=https://api.sipgate.com/v2/doc/#/sessions/newCall|title=Sipgate API Documentation|access-date=July 10, 2018|archive-url=https://web.archive.org/web/20180710163601/https://api.sipgate.com/v2/doc#/sessions/newCall|archive-date=July 10, 2018|url-status=live}}</ref> Shopify uses this code when the store has not paid their fees and is temporarily disabled.<ref>{{cite web|url=https://help.shopify.com/en/api/getting-started/response-status-codes|title=Shopify Documentation|access-date=July 25, 2018|archive-url=https://web.archive.org/web/20180725122914/https://help.shopify.com/en/api/getting-started/response-status-codes|archive-date=July 25, 2018|url-status=live}}</ref> Stripe uses this code for failed payments where parameters were correct, for example blocked fraudulent payments.<ref>{{cite web |title=Stripe API Reference – Errors |url=https://stripe.com/docs/api/errors |website=stripe.com |access-date=28 October 2019 |ref=errors-402-RequestFailed}}</ref> Cloudflare Turnstile uses this code when requesting resources with cURL. x402 is an open standard that repurposes the HTTP 402 "Payment Required" status code. ;{{anchor|403}}403 Forbidden :{{main|HTTP 403}} : The request was valid, but the server refuses action. This may be due to the user not having permission to a resource or needing an account of some sort, or attempting a prohibited action (e.g. creating a duplicate record where only one is allowed). This code is also typically used if the request provided authentication by answering the WWW-Authenticate header field challenge, but the server did not accept that authentication. The request should not be repeated. : This code differs from 401 in that while 401 is returned when the client has not authenticated, and implies that a successful response may be returned following valid authentication, 403 is returned when the client is not permitted access to the resource despite providing authentication such as insufficient permissions of the authenticated account. : The Apache web server returns 403 in response to a request for URL<ref name="RFC" /> paths that corresponded to a file system directory when directory listing is disabled and there is no Directory Index directive to specify an existing file to be returned to the browser. Some administrators configure the Mod proxy extension to block such requests and this will also return 403. IIS responds in the same way when directory listings are denied in that server. In WebDAV, 403 is returned if the client issued a PROPFIND request but did not also issue the required Depth header or issued a Depth header of infinity.<ref name="RFC">{{cite web |url = http://www.webdav.org/specs/rfc4918.html#rfc.section.9.1.1 |title = HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV) |date = June 2007 |publisher = IETF |access-date = January 12, 2016 |url-status = dead |archive-url = https://web.archive.org/web/20160303200436/http://www.webdav.org/specs/rfc4918.html#rfc.section.9.1.1 |archive-date = March 3, 2016 }}</ref> ;{{anchor|404}}404 Not Found :{{main|HTTP 404}} : The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible. ;{{anchor|405}}405 Method Not Allowed : A request method is not supported for the requested resource (for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource). ;{{anchor|406}}406 Not Acceptable : The requested resource is capable of generating only content not acceptable according to the Accept headers sent in the request. See Content negotiation. ;{{anchor|407}}407 Proxy Authentication Required :The client must first authenticate itself with the proxy. ;{{anchor|408}}408 Request Timeout : The server timed out waiting for the request. According to HTTP specifications: "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." ;{{anchor|409}}409 Conflict : Indicates that the request could not be processed because of conflict in the current state of the resource, such as an edit conflict between multiple simultaneous updates.<ref>{{cite web |title=409 Conflict |url=https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Status/409 |website=MDN Web Docs |access-date=11 June 2025 |date=13 March 2025}}</ref> ;{{anchor|410}}410 Gone : Indicates that the resource requested was previously in use but is no longer available and will not be available again. This should be used when a resource has been intentionally removed and the resource should be purged. Upon receiving a 410 status code, the client should not request the resource in the future. Clients such as search engines should remove the resource from their indices. Most use cases do not require clients and search engines to purge the resource, and a "404 Not Found" may be used instead. ;{{anchor|411}}411 Length Required : The request did not specify the length of its content, which is required by the requested resource. ;{{anchor|412}}412 Precondition Failed : The server does not meet one of the preconditions that the requester put on the request header fields. ;{{anchor|413}}413 Content Too Large : The request is larger than the server is willing or able to process. Previously called "Request Entity Too Large" and "Payload Too Large".{{Ref RFC|2616|rsection=10.4.14}}{{Ref RFC|9110|rsection=15.5.14}} ;{{anchor|414}}414 URI Too Long : The URI provided was too long for the server to process. Often the result of too much data being encoded as a query-string of a GET request, in which case it should be converted to a POST request. Called "Request-URI Too Long" previously.{{Ref RFC|2616|rsection=10.4.15}} ;{{anchor|415}}415 Unsupported Media Type : The request entity has a media type which the server or resource does not support. For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format. ;{{anchor|416}}416 Range Not Satisfiable : The client has asked for a portion of the file (byte serving), but the server cannot supply that portion. For example, if the client asked for a part of the file that lies beyond the end of the file. Called "Requested Range Not Satisfiable" previously.{{Ref RFC|2616|rsection=10.4.17}} ;{{anchor|417}}417 Expectation Failed : The server cannot meet the requirements of the Expect request-header field.<ref>{{cite web |last1=TheDeadLike |title=HTTP/1.1 Status Codes 400 and 417, cannot choose which |url=http://serverfault.com/questions/433470/http-1-1-status-codes-400-and-417-cannot-choose-which |url-status=live |archive-url=https://web.archive.org/web/20151010125107/http://serverfault.com/questions/433470/http-1-1-status-codes-400-and-417-cannot-choose-which |archive-date=October 10, 2015 |access-date=16 October 2015 |website=serverFault}}</ref> <!-- The following code is under discussion on the talk page. Please discuss there before removing this entry. --> ;{{anchor|418}}418 I'm a teapot (RFC 2324, RFC 7168) :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. The RFC specifies this code should be returned by teapots requested to brew coffee.{{Ref RFC|2324|quote=Any attempt to brew coffee with a teapot should result in the error code "418 I'm a teapot". The resulting entity body MAY be short and stout.}} This HTTP status is used as an Easter egg in some websites, such as Google.com's "I'm a teapot" easter egg.<ref>{{cite news |url=http://searchengineland.com/new-google-easter-egg-seo-geeks-server-status-418-im-teapot-201739 |author=Barry Schwartz |date=26 August 2014 |title=New Google Easter Egg For SEO Geeks: Server Status 418, I'm A Teapot |work=Search Engine Land |access-date=November 4, 2015 |archive-url=https://web.archive.org/web/20151115041951/http://searchengineland.com/new-google-easter-egg-seo-geeks-server-status-418-im-teapot-201739 |archive-date=November 15, 2015 |url-status=dead}}</ref><ref>{{Cite web |url=https://www.google.com/teapot |title=Error 418 (I'm a teapot)!? |access-date=December 17, 2025}}{{cbignore}}</ref> Sometimes, this status code is also used as a response to a blocked request, instead of the more appropriate 403 Forbidden.<ref>{{cite web|url=https://help.dreamhost.com/hc/en-us/articles/215947927-Enable-extra-web-security-on-a-website|title=Enable extra web security on a website|access-date=2022-12-18|website=DreamHost|language=en}}</ref><ref>{{Cite web|url=https://www.pcmag.com/news/i-went-to-a-russian-website-and-all-i-got-was-this-lousy-teapot|title=I Went to a Russian Website and All I Got Was This Lousy Teapot|access-date=2022-12-18|website=PCMag|date=February 25, 2022 |language=en}}</ref> ;{{anchor|421}}421 Misdirected Request : The request was directed at a server that is not able to produce a response (for example because of connection reuse). ;{{anchor|422}}422 Unprocessable Content : The request was well-formed (i.e., syntactically correct) but could not be processed.{{Ref RFC|9110|rsection=15.5.21}} ;{{anchor|423}}423 Locked (WebDAV; RFC 4918) : The resource that is being accessed is locked.{{Ref RFC|4918}} ;{{anchor|424}}424 Failed Dependency (WebDAV; RFC 4918) : The request failed because it depended on another request and that request failed (e.g., a PROPPATCH).{{Ref RFC|4918}} ;{{anchor|425}}425 Too Early (RFC 8470) :Indicates that the server is unwilling to risk processing a request that might be replayed. ;{{anchor|426}}426 Upgrade Required : The client should switch to a different protocol such as TLS/1.3, given in the Upgrade header field. ;{{anchor|428}}428 Precondition Required (RFC 6585) :The origin server requires the request to be conditional. Intended to prevent 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.{{Ref RFC|6585}} ;{{anchor|429}}429 Too Many Requests (RFC 6585) :The user has sent too many requests in a given amount of time. Intended for use with rate-limiting schemes.<ref name="rfc6585" /> ;{{anchor|431}}431 Request Header Fields Too Large (RFC 6585) :The server is unwilling to process the request because either an individual header field, or all the header fields collectively, are too large.<ref name="rfc6585" /> ;{{anchor|451}}451 Unavailable For Legal Reasons (RFC 7725) : A server operator has received a legal demand to deny access to a resource or to a set of resources that includes the requested resource.<ref>{{cite web|title=An HTTP Status Code to Report Legal Obstacles|url=https://tools.ietf.org/html/rfc7725|date=February 2016|last=Bray|first=T.|access-date=7 March 2015|website=ietf.org|archive-url=https://web.archive.org/web/20160304040017/http://tools.ietf.org/html/rfc7725|archive-date=March 4, 2016|url-status=live}}</ref> The code 451 was chosen as a reference to the novel ''Fahrenheit 451''.<ref>{{Cite news |last=Paul |first=Ian |date=21 Dec 2015 |title=Error 451 is the new Ray Bradbury-inspired HTTP code for online censorship |url=https://www.pcworld.com/article/418860/error-451-is-the-new-ray-bradbury-inspired-http-code-for-online-censorship.html |access-date=18 July 2025 |work=PC World}}</ref> {{See also |HTTP 451}}
===<span class="anchor" id="server errors"></span><span class="anchor" id="5xx server errors"></span>5xx server error=== 5xx status indicates that the server is aware that it has encountered an error or is otherwise incapable of performing the request. Except when responding to a HEAD request, the server {{em|should}} include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents {{em|should}} display any included entity to the user. These response codes are applicable to any request method.
;{{anchor|500|Internal Server Error}}500 Internal Server Error : A generic error message, given when an unexpected condition was encountered and no more specific message is suitable. ;{{anchor|501|Not Implemented}}501 Not Implemented : The server either does not recognize the request method, or it lacks the ability to fulfil the request. Usually this implies future availability (e.g., a new feature of a web-service API). ;{{anchor|502|Bad Gateway}}502 Bad Gateway : The server was acting as a gateway or proxy and received an invalid response from the upstream server. ;{{anchor|503|Service Unavailable}}503 Service Unavailable : The server cannot handle the request (because it is overloaded or down for maintenance). Generally, this is a temporary state.<ref>{{cite web|last1=alex|title=What is the correct HTTP status code to send when a site is down for maintenance?|url=https://stackoverflow.com/questions/2786595/what-is-the-correct-http-status-code-to-send-when-a-site-is-down-for-maintenance|website=Stack Overflow|access-date=16 October 2015|archive-url=https://web.archive.org/web/20161011013125/https://stackoverflow.com/questions/2786595/what-is-the-correct-http-status-code-to-send-when-a-site-is-down-for-maintenance|archive-date=October 11, 2016|url-status=live}}</ref> ;{{anchor|504|Gateway Timeout}}504 Gateway Timeout : The server was acting as a gateway or proxy and did not receive a timely response from the upstream server. ;{{anchor|505|HTTP Version Not Supported}}505 HTTP Version Not Supported : The server does not support the HTTP version used in the request. ;{{anchor|506|Variant Also Negotiates|RFC 2295|2295}}506 Variant Also Negotiates (RFC 2295) : Transparent content negotiation for the request results in a circular reference.{{Ref RFC|2295}} ;{{anchor|507|Insufficient Storage|RFC 4918|4918}}507 Insufficient Storage (WebDAV; RFC 4918) : The server is unable to store the representation needed to complete the request.{{Ref RFC|4918}} ;{{anchor|508|Loop Detected|RFC 5842|5842}}508 Loop Detected (WebDAV; RFC 5842) : The server detected an infinite loop while processing the request (sent instead of 208 Already Reported). ;{{anchor|510|Not Extended|RFC 2774|2774}}510 Not Extended (RFC 2774) : Further extensions to the request are required for the server to fulfil it.{{Ref RFC|2774}} ;{{anchor|511|Network Authentication Required|RFC 6585|6585}}511 Network Authentication Required (RFC 6585) :The client needs to authenticate to gain network access. Intended for use by intercepting proxies used to control access to the network (e.g., "captive portals" used to require agreement to Terms of Service before granting full Internet access via a Wi-Fi hotspot).<ref name="rfc6585" /> :{{Anchor|unofficial}}
==Nonstandard codes== The following codes are used by various web servers but not specified by an IETF standard.
=== Internet Information Services === Microsoft's Internet Information Services (IIS) web server expands the 4xx error space to signal errors with the client's request. IIS sometimes uses additional decimal sub-codes for more specific information,<ref>{{cite web|url=http://support.microsoft.com/kb/943891/|title=The HTTP status codes in IIS 7.0|date=July 14, 2009|publisher=Microsoft|url-status=live|archive-url=https://web.archive.org/web/20090409091609/http://support.microsoft.com/kb/943891|archive-date=April 9, 2009|access-date=April 1, 2009}}</ref> however these sub-codes only appear in the response payload and in documentation, not in the place of an actual HTTP status code.
; {{anchor|440-MS}} 440 Login Time-out : The client's session has expired and must log in again.<ref>{{cite web|url=https://support.microsoft.com/en-us/help/941201/|title=Error message when you try to log on to Exchange 2007 by using Outlook Web Access: "440 Login Time-out"|year=2010|publisher=Microsoft|access-date=November 13, 2013}}</ref> ; {{anchor|449-MS}} 449 Retry With : The server cannot honor the request because the user has not provided the required information.<ref>{{cite web |url=http://msdn.microsoft.com/en-us/library/dd891478(PROT.10).aspx |title=2.2.6 449 Retry With Status Code |year=2009 |publisher=Microsoft |access-date=October 26, 2009 |archive-url=https://web.archive.org/web/20091005090136/http://msdn.microsoft.com/en-us/library/dd891478(PROT.10).aspx |archive-date=October 5, 2009 |url-status=live}}</ref> ; {{anchor|450-MS}} 450 Blocked by Windows Parental Controls : Indicates that Windows Parental Controls block access to the requested webpage.<ref>{{cite web|url=https://public.bn1.livefilestore.com/y1pJXeg_sNOONKwMraE-xmZFWAfZF6COAKnyfgc-2ykUof743pV4XuRqm14pj-b_yK8Km4sfSR6mU5OhLrupZ8dFg|title=Screenshot of error page|format=bmp|access-date=October 11, 2009|archive-url=https://web.archive.org/web/20130511045107/https://public.bn1.livefilestore.com/y1pJXeg_sNOONKwMraE-xmZFWAfZF6COAKnyfgc-2ykUof743pV4XuRqm14pj-b_yK8Km4sfSR6mU5OhLrupZ8dFg|archive-date=May 11, 2013|url-status=dead}}</ref> ; {{anchor|451-MS}} 451 Redirect : Used in Exchange ActiveSync when either a more efficient server is available or the server cannot access the users' mailbox.<ref>{{cite web |title=MS-ASCMD, Section 3.1.5.2.2 |url=http://msdn.microsoft.com/en-us/library/gg651019 |publisher=Msdn.microsoft.com |access-date=January 8, 2015 |archive-url=https://web.archive.org/web/20150326120838/https://msdn.microsoft.com/en-us/library/gg651019 |archive-date=March 26, 2015 |url-status=live}}</ref> The client is expected to re-run the HTTP AutoDiscover operation to find a more appropriate server.<ref>{{cite web|title=Ms-oxdisco|url=http://msdn.microsoft.com/en-us/library/cc433481|publisher=Msdn.microsoft.com|access-date=January 8, 2015|archive-url=https://web.archive.org/web/20140731074358/http://msdn.microsoft.com/en-us/library/cc433481|archive-date=July 31, 2014|url-status=live}}</ref>
=== nginx === The nginx web server software expands the 4xx error space to signal issues with the client's request.<ref>{{cite web|url=http://lxr.nginx.org/source/src/http/ngx_http_request.h|title=ngx_http_request.h|work=nginx 1.9.5 source code|publisher=nginx inc.|access-date=2016-01-09|archive-url=https://web.archive.org/web/20170919111558/http://lxr.nginx.org/source/src/http/ngx_http_request.h|archive-date=September 19, 2017|url-status=dead}}</ref><ref>{{cite web|url=http://lxr.nginx.org/source/src/http/ngx_http_special_response.c|title=ngx_http_special_response.c|work=nginx 1.9.5 source code|publisher=nginx inc.|access-date=2016-01-09|archive-url=https://web.archive.org/web/20180508052017/http://lxr.nginx.org/source/src/http/ngx_http_special_response.c|archive-date=May 8, 2018|url-status=dead}}</ref> ; {{anchor|444-nginx}} 444 No Response : Used internally<ref>[http://nginx.org/en/docs/http/ngx_http_rewrite_module.html#return "return" directive] {{Webarchive|url=https://web.archive.org/web/20180301164309/http://nginx.org/en/docs/http/ngx_http_rewrite_module.html#return |date=March 1, 2018}} (http_rewrite module) documentation.</ref> to instruct the server to return no information to the client and close the connection immediately. ; {{anchor|494-nginx}} 494 Request header too large : Client sent too large request or too long header line. ; {{anchor|495-nginx}} 495 SSL Certificate Error :An expansion of the 400 Bad Request response code, used when the client has provided an invalid client certificate. ; {{anchor|496-nginx}} 496 SSL Certificate Required : An expansion of the 400 Bad Request response code, used when a client certificate is required but not provided. ; {{anchor|497-nginx}} 497 HTTP Request Sent to HTTPS Port : An expansion of the 400 Bad Request response code, used when the client has made a HTTP request to a port listening for HTTPS requests. ; {{anchor|499-nginx}} 499 Client Closed Request : Used when the client has closed the request before the server could send a response.
=== Cloudflare === Cloudflare's reverse proxy service expands the 5xx series of errors space to signal issues with the origin server.<ref>{{cite web|url=https://support.cloudflare.com/hc/en-us/articles/115003014432-HTTP-Status-Codes|title=Troubleshooting: Error Pages|publisher=Cloudflare|access-date=2016-01-09|archive-url=https://web.archive.org/web/20160304035212/https://support.cloudflare.com/hc/en-us/sections/200820298-Error-Pages|archive-date=March 4, 2016|url-status=dead}}</ref>
; {{anchor|520-cloudflare}} 520 Web Server Returned an Unknown Error : The origin server returned an empty, unknown, or unexpected response to Cloudflare.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-520/|title=Error 520: web server returns an unknown error|date=May 29, 2025 |publisher=Cloudflare}}</ref> ; {{anchor|521-cloudflare}} 521 Web Server Is Down : The origin server refused connections from Cloudflare. Security solutions at the origin may be blocking legitimate connections from certain Cloudflare IP addresses.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-521/|title=Error 521: web server is down|date=April 29, 2025 |publisher=Cloudflare}}</ref> ; {{anchor|522-cloudflare}} 522 Connection Timed Out : Cloudflare timed out contacting the origin server.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-522/|title=Error 522: connection timed out|date=May 5, 2025 |publisher=Cloudflare}}</ref> ; {{anchor|523-cloudflare}} 523 Origin Is Unreachable : Cloudflare could not contact the origin server.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-523/|title=Error 523: origin is unreachable|date=April 29, 2025 |publisher=Cloudflare}}</ref> ; {{anchor|524-cloudflare}} 524 A Timeout Occurred : Cloudflare was able to complete a TCP connection to the origin server, but the origin did not provide a timely HTTP response.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-524/|title=Error 524: a timeout occurred|date=August 6, 2025 |publisher=Cloudflare}}</ref> ; {{anchor|525-cloudflare}} 525 SSL Handshake Failed : Cloudflare could not negotiate a SSL/TLS handshake with the origin server.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-525/|title=Error 525: SSL handshake failed|date=April 29, 2025 |publisher=Cloudflare}}</ref><ref>{{cite web |url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-525/ |title=Cloudflare support docs |access-date=September 14, 2025 |website=developers.cloudflare.com |date=April 29, 2025 }}</ref> ; {{anchor|526-cloudflare}} 526 Invalid SSL Certificate : Cloudflare could not validate the SSL certificate on the origin web server.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-526/|title=Error 526: invalid SSL certificate|date=August 11, 2025 |publisher=Cloudflare}}</ref><ref>{{cite web |url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-526/ |title=Cloudflare support docs |access-date=September 14, 2025 |website=developers.cloudflare.com |date=August 11, 2025 }}</ref> Also used by Cloud Foundry's gorouter. ; {{anchor|527-cloudflare}} 527 Railgun Error (obsolete) : Error 527 indicated an interrupted connection between Cloudflare and the origin server's Railgun server.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/cloudflare-errors/troubleshooting-cloudflare-5xx-errors/#527-error-railgun-listener-to-origin-error|title=527 Error: Railgun Listener to origin error|publisher=Cloudflare|access-date=2016-10-12|archive-url=https://web.archive.org/web/20161013152120/https://support.cloudflare.com/hc/en-us/articles/217891268-527-Railgun-Listener-to-Origin-Error|archive-date=October 13, 2016|url-status=dead}}</ref> This error is obsolete as Cloudflare has deprecated Railgun. ; {{anchor|530-cloudflare}} 530 Origin Unavailable : Cloudflare was unable to resolve the origin hostname, preventing it from establishing a connection to the origin server. The body of the response contains an 1xxx error.<ref>{{cite web|url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-530/|title=Error 530|publisher=Cloudflare|access-date=2019-11-01}}</ref><ref>{{cite web |url=https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-530/ |title=Cloudflare support docs |access-date=September 14, 2025 |website=developers.cloudflare.com |date=April 29, 2025 }}</ref>
=== AWS Elastic Load Balancing === Amazon Web Services' Elastic Load Balancing adds a few custom return codes to signal issues either with the client request or with the origin server.<ref name="aws.amazon.com">{{Cite web|url=https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-troubleshooting.html|title=Troubleshoot Your Application Load Balancers – Elastic Load Balancing|website=docs.aws.amazon.com|access-date=2023-05-17}}</ref> ; {{Anchor|000-ec2}} 000 : Returned with an HTTP/2 GOAWAY frame if the compressed length of any of the headers exceeds 8K bytes or if more than 10K requests are served through one connection.<ref name="aws.amazon.com" /> ; {{Anchor|460-ec2}} 460 : Client closed the connection with the load balancer before the idle timeout period elapsed. Typically, when client timeout is sooner than the Elastic Load Balancer's timeout.<ref name="aws.amazon.com" /> ; {{Anchor|463-ec2}} 463 : The load balancer received an X-Forwarded-For request header with more than 30 IP addresses.<ref name="aws.amazon.com" /> ; {{Anchor|464-ec2}} 464 : Incompatible protocol versions between Client and Origin server.<ref name="aws.amazon.com" /> ; {{Anchor|561-ec2}} 561 Unauthorized : An error around authentication returned by a server registered with a load balancer. A listener rule is configured to authenticate users, but the identity provider (IdP) returned an error code when authenticating the user.<ref name="aws.amazon.com" />
===Apache=== Used by Apache HTTP Server. ; {{anchor|509-apache}} 509 Bandwidth Limit Exceeded : The server has exceeded the bandwidth specified by the server administrator; this is often used by shared hosting providers to limit the bandwidth of customers.<ref>{{cite web|url=https://documentation.cpanel.net/display/CKB/HTTP+Error+Codes+and+Quick+Fixes#HTTPErrorCodesandQuickFixes-509BandwidthLimitExceeded|title=HTTP Error Codes and Quick Fixes|publisher=Docs.cpanel.net|access-date=October 15, 2015|archive-url=https://web.archive.org/web/20151123100640/https://documentation.cpanel.net/display/CKB/HTTP+Error+Codes+and+Quick+Fixes#HTTPErrorCodesandQuickFixes-509BandwidthLimitExceeded|archive-date=November 23, 2015|url-status=dead}}</ref> Also used by cPanel.
===Laravel framework=== Used by Laravel Framework.
; {{anchor|419-laravel}} 419 Page Expired : A CSRF Token is missing or expired.<ref>{{cite web|title=framework/src/Illuminate/Foundation/Exceptions/Handler.php|website=GitHub |url=https://github.com/laravel/framework/blob/57ae89a8acbc316153315272a4af2e68370f5e36/src/Illuminate/Foundation/Exceptions/Handler.php#L492|access-date=December 12, 2023}}</ref>
===Spring Framework=== Used by Spring Framework. ; {{anchor|420-spring}} 420 Method Failure : A deprecated response status proposed during the development of WebDAV<ref>{{cite web|title=draft-ietf-webdav-protocol-05: Extensions for Distributed Authoring on the World Wide Web -- WEBDAV|url=https://datatracker.ietf.org/doc/html/draft-ietf-webdav-protocol-05#section-10.5}}</ref> used by the Spring Framework when a method has failed.<ref>{{cite web|title=Enum HttpStatus|url=https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/http/HttpStatus.html|website=Spring Framework|publisher=org.springframework.http|access-date=16 October 2015|archive-url=https://web.archive.org/web/20151025102238/http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/http/HttpStatus.html|archive-date=October 25, 2015|url-status=live}}</ref>
===Twitter=== Used by Twitter.
; 420 Enhance Your Calm : Returned by version 1 of the Twitter Search and Trends API when the client is being rate limited; versions 1.1 and later use the 429 Too Many Requests response code instead.<ref>{{cite web|url=https://developer.twitter.com/en/docs/basics/response-codes|title=Twitter Error Codes & Responses|year=2014|publisher=Twitter|access-date=January 20, 2014|archive-url=https://web.archive.org/web/20170927155109/https://developer.twitter.com/en/docs/basics/response-codes|archive-date=September 27, 2017|url-status=dead}}</ref> The phrase "Enhance your calm" comes from the 1993 movie ''Demolition Man'', and its association with this number is likely a reference to cannabis.{{Citation needed|date=August 2020}}
===Shopify=== Used by Shopify.
; 430 Request Header Fields Too Large : A deprecated response used by Shopify, instead of the 429 Too Many Requests response code, when too many URLs are requested within a certain time frame.<ref>{{Cite web|url=https://www.contentkingapp.com/academy/http-status-codes/|title=HTTP Status Codes and SEO: what you need to know|website=ContentKing|language=en|access-date=2019-08-09}}</ref> ; 430 Shopify Security Rejection : Used by Shopify to signal that the request was deemed malicious.<ref name="shopify-api">{{Cite web|url=https://shopify.dev/docs/api/usage/response-codes|title=Shopify API response status and error codes|language=en|access-date=December 12, 2023}}</ref> ; 530 Origin DNS Error : Indicates that Cloudflare can't resolve the requested DNS record.<ref name="shopify-api" /> ; {{anchor|540-shopify}} 540 Temporarily Disabled : Indicates that the requested endpoint has been temporarily disabled.<ref name="shopify-api" /> ; {{anchor|783-shopify}} 783 Unexpected Token : Indicates that the request includes a JSON syntax error.<ref name="shopify-api" />
===ArcGIS Server=== Used by ArcGIS Server.
; {{anchor|498-arcgis}} 498 Invalid Token : Indicates an expired or otherwise invalid token.<ref name="arcgis">{{cite web|url=http://help.arcgis.com/en/arcgisserver/10.0/apis/soap/index.htm#Using_token_authentication.htm|title=Using token-based authentication|website=ArcGIS Server SOAP SDK|access-date=September 8, 2014|archive-url=https://web.archive.org/web/20140926033953/http://help.arcgis.com/en/arcgisserver/10.0/apis/soap/index.htm#Using_token_authentication.htm|archive-date=September 26, 2014|url-status=dead}}</ref> ; {{anchor|499-arcgis}} 499 Token Required : Indicates that a token is required but was not submitted.<ref name="arcgis" />
===cPanel=== Used by cPanel.
; {{anchor|508-cpanel}} 508 Resource Limit Is Reached : Used instead of 503 when the server's account has exceeded the resources assigned to it, such as CPU/RAM usage or number of concurrent processes.<ref>{{cite web|url=https://support.cpanel.net/hc/en-us/articles/360057457313-Receiving-a-508-Resource-Limit-Is-Reached-error-when-browsing-a-site-on-CloudLinux|title=Receiving a "508 Resource Limit Is Reached" error when browsing a site on CloudLinux|date=September 28, 2021 |access-date=July 19, 2025|archive-url=https://web.archive.org/web/20250719083333/https://support.cpanel.net/hc/en-us/articles/360057457313-Receiving-a-508-Resource-Limit-Is-Reached-error-when-browsing-a-site-on-CloudLinux|archive-date=July 19, 2025}}</ref>
===SSLLabs server testing API=== Used by Qualys in the SSLLabs server testing API.
; {{anchor|529-ssllabs}} 529 Site is overloaded : Signals that the site can not process the request.<ref>{{cite web |url=https://github.com/ssllabs/ssllabs-scan/blob/master/ssllabs-api-docs-v3.md#error-response-status-codes |title=SSL Labs API v3 Documentation |website=github.com}}</ref>
===Pantheon Systems web platform=== Used by the Pantheon Systems web platform.
; {{anchor|530-pantheon}} 530 Site is frozen : Indicates a site that has been frozen due to inactivity.<ref>{{cite web |url=https://pantheon.io/docs/platform-considerations/ |title=Platform Considerations {{!}} Pantheon Docs |website=pantheon.io |access-date=January 5, 2017 |archive-url=https://web.archive.org/web/20170106011710/https://pantheon.io/docs/platform-considerations/ |archive-date=January 6, 2017 |url-status=dead}}</ref>
===LinkedIn=== Used by LinkedIn.
; {{anchor|999-linkedin}} 999 Request denied : Related to being blocked/walled or unable to access their webpages without first signing in.<ref>[https://learn.microsoft.com/en-us/archive/msdn-technet-forums/5a4f8eb5-bf1b-4776-b4bb-4baef621838f Seen in 2017], [https://archive.today/20240907164007/https://ipfs.desmos.network/ipfs/QmeoH4jKZG4SS6nuviqZeuiDggisYGitucvk7GrP3wrRZT/archive.is/www.linkedin.com/in/gregorybarr 2024] and [https://github.com/sherlock-project/sherlock/issues/2652 2025 examples]</ref>
===Miscellaneous=== ; {{anchor|218-apache}} {{anchor|218-misc}} 218 This is fine : An informal catch-all error condition, widely attributed to the Apache HTTP server to allow for the passage of message bodies through the server when the <code>ProxyErrorOverride</code> setting is enabled, though the status code and behavior is not part of any official Apache specification. The association between this status code and Apache has been attributed to unsourced additions to Wikipedia, which were subsequently picked up by other reference material, creating circular references.<ref>{{cite web|title=218 This is fine – HTTP status code explained|url=https://http.dev/218|website=HTTP.dev|access-date=25 July 2023}}</ref> ; {{anchor|598-misc}} 598 Network read timeout error : An informal convention used by some HTTP proxies to signal a network read timeout behind the proxy to a client in front of the proxy.<ref>{{Cite web|url=http://www.ascii-code.com/http-status-codes.php|title=HTTP status codes – ascii-code.com|website=www.ascii-code.com|access-date=2016-12-23|archive-url=https://web.archive.org/web/20170107115008/http://www.ascii-code.com/http-status-codes.php|archive-date=January 7, 2017|url-status=dead}}</ref> ; {{Anchor|599-misc}} 599 Network Connect Timeout Error : An error used by some HTTP proxies to signal a network connect timeout behind the proxy to a client in front of the proxy.
== See also == * Custom error pages * List of FTP server return codes * List of HTTP header fields * List of SMTP server return codes * Common Log Format * x402 {{ndash}} an open standard for that repurposes the HTTP 402 "Payment Required" status code.
== References == {{Reflist}}
== External links == {{Commons category|HTTP status codes}} * [https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml Hypertext Transfer Protocol (HTTP) Status Code Registry] at the ''Internet Assigned Numbers Authority'' * [https://developer.mozilla.org/en-US/docs/Web/HTTP/Status MDN status code reference] at ''mozilla.org'' {{Error messages}}
Category:Hypertext Transfer Protocol status codes HTTP status codes