| HTTP |
|---|
 |
| Request methods |
| Header fields |
| Response status codes |
| Security access control methods |
| Security vulnerabilities |
This article lists standard and notable non-standardHTTP header fields.
A core set of fields is standardized by theInternet Engineering Task Force (IETF) inRFC 9110 and9111. TheField Names,Header Fields andRepository of Provisional Registrations are maintained by theIANA. Additional fields may be defined by aweb application.
In the past, non-standard header field names were prefixed withX- but this convention was deprecated in June 2012 because of the inconveniences it caused when non-standard fields became standard.[1] An earlier restriction on use ofDowngraded- was lifted in March 2013.[2]
A few field values can contain comments (i.e. in User-Agent, Server, Via fields), which can be ignored by software.[3]
Many field values may contain a quality (q) key-value pair separated byequals sign, specifying a weight to use incontent negotiation.[4] For example, a browser may indicate that it accepts information in German or English, with German as preferred by setting theq value forde higher than that ofen, as follows:
Accept-Language: de; q=1.0, en; q=0.5
This section lists header fields used in arequest.
[RFC 3229, permanent] Acceptable instance-manipulations for the request.[5]
For example:A-IM: feed
[RFC 9110, permanent]Media type(s) that is/are acceptable for the response. SeeContent negotiation.
For example:Accept: text/html
[RFC 9110, permanent] Character sets that are acceptable.
For example:Accept-Charset: utf-8
[RFC 7089, provisional] Acceptable version in time.
For example:Accept-Datetime: Thu, 31 May 2007 20:35:00 GMT
[RFC 9110, permanent] List of acceptable encodings. SeeHTTP compression.
For example:Accept-Encoding: gzip, deflate
[RFC 9110, permanent] List of acceptable human languages for response. SeeContent negotiation.
For example:Accept-Language: en-US
[permanent] Initiates a request forcross-origin resource sharing withOrigin (below).[6]
For example:Access-Control-Request-Method: GET
[RFC 9110, permanent] Authentication credentials forHTTP authentication.
For example:Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
[RFC 9111, permanent] Used to specify directives thatmust be obeyed by all caching mechanisms along the request-response chain. Per HTTP/1.1, theno-cache value allows the browser to tell the server and intermediate caches that it wants a fresh version of the resource. The HTTP/1.0,Pragma: no-cache header field has the same purpose.[7]
The behavior ofPragma: no-cache in aresponse is not specified yet some user agents support it.[8] HTTP/1.1 specifically warns against relying on this behavior.
For example:Cache-Control: no-cache
[RFC 9110, permanent] Control options for the current connection and list of hop-by-hop request fields.[9]Must not be used with HTTP/2.[10]
For example:Connection: keep-aliveConnection: Upgrade
[RFC 9110, permanent] The type of encoding used on the data. SeeHTTP compression.
For example:Content-Encoding: gzip
[RFC 9110, permanent] The length of the request body inoctets (8-bit bytes).
For example:Content-Length: 348
[RFC 1544, 1864, 4021, obsolete] ABase64-encoded binaryMD5 sum of the content of the request body.[11]
For example:Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ==
[RFC 9110, permanent] TheMedia type of the body of the request (used with POST and PUT requests).
For example:Content-Type: application/x-www-form-urlencoded
[RFC 2965, 6265, permanent] AnHTTP cookie previously sent by the server withSet-Cookie (below).
For example:Cookie: $Version=1; Skin=new;
[RFC 9110, permanent] The date and time at which the message was originated (in "HTTP-date" format as defined byRFC 9110: HTTP Semantics, section 5.6.7 "Date/Time Formats").
For example:Date: Tue, 15 Nov 1994 08:12:31 GMT
[RFC 9110, permanent] Indicates that particular server behaviors are required by the client.
For example:Expect: 100-continue
[RFC 7239, permanent] Disclose original information of a client connecting to a web server through an HTTP proxy.[12]
For example:Forwarded: for=192.0.2.60;proto=http;by=203.0.113.43Forwarded: for=192.0.2.43, for=198.51.100.17
[RFC 9110, permanent] The email address of the user making the request.
For example:From: user@example.com
[RFC 9110, 9113, permanent] The domain name of the server (forvirtual hosting), and theTCP port number on which the server is listening. Theport number may be omitted if the port is the standard port for the service requested. Mandatory since HTTP/1.1.[13] If the request is generated directly in HTTP/2, it should not be used.[14]
For example:Host: en.wikipedia.org:8080Host: en.wikipedia.org
[RFC 7540, 9113, obsolete] A request that upgrades from HTTP/1.1 to HTTP/2 MUST include exactly oneHTTP2-Settings header field. TheHTTP2-Settings header field is a connection-specific header field that includes parameters that govern the HTTP/2 connection, provided in anticipation of the server accepting the request to upgrade.[15][16]
For example:HTTP2-Settings: token64
[RFC 9110, permanent] Only perform the action if the client supplied entity matches the same entity on the server. This is mainly for methods like PUT to only update a resource if it has not been modified since the user last updated it.
For example:If-Match: "737060cd8c284d8af7ad3082f209582d"
[RFC 9110, permanent] Allows a304 Not Modified to be returned if content is unchanged.
For example:If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
[RFC 9110, permanent] Allows a304 Not Modified to be returned if content is unchanged, seeHTTP ETag.
For example:If-None-Match: "737060cd8c284d8af7ad3082f209582d"
[RFC 9110, permanent] If the entity is unchanged, send me the part(s) that I am missing; otherwise, send me the entire new entity.
For example:If-Range: "737060cd8c284d8af7ad3082f209582d"
[RFC 9110, permanent] Only send the response if the entity has not been modified since a specific time.
For example:If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
[RFC 9110, permanent] Limit the number of times the message can be forwarded through proxies or gateways.
For example:Max-Forwards: 10
[RFC 6454, permanent] Initiates a request forcross-origin resource sharing (asks server forAccess-Control-* response fields).[6]
For example:Origin: http://www.example-social-network.com
[RFC 9111, outdated] Implementation-specific fields that may have various effects anywhere along the request-response chain.
For example:Pragma: no-cache
[RFC 7240, permanent] Allows client to request that certain behaviors be employed by a server while processing a request.
For example:Prefer: return=representation
[RFC 9110, permanent] Authorization credentials for connecting to a proxy.
For example:Proxy-Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
[RFC 9110, permanent] Request only part of an entity. Bytes are numbered from 0. SeeByte serving.
For example:Range: bytes=500-999
[RFC 9110, permanent] The address of the previous web page from which a link to the currently requested page was followed.
Although the intended term is actually spelled "referrer", the misspelling is in the RFC as well as in most implementations, and is therefore considered correct terminology.
For example:Referer: http://en.wikipedia.org/wiki/Main_Page
[RFC 9110, permanent] The transfer encodings the user agent is willing to accept: the same values as for the response header field Transfer-Encoding can be used, plus the "trailers" value (related to the "chunked" transfer method) to notify the server it expects to receive additional fields in the trailer after the last, zero-sized, chunk. Onlytrailers is supported in HTTP/2.[10]
For example:TE: trailers,deflate
[RFC 9110, permanent] The Trailer general field value indicates that the given set of header fields is present in the trailer of a message encoded withchunked transfer coding.
For example:Trailer: Max-Forwards
[RFC 9110, permanent] The form of encoding used to safely transfer the entity to the user.Currently defined methods are:chunked, compress, deflate, gzip, identity. Must not be used with HTTP/2.[10]
For example:Transfer-Encoding: chunked
[RFC 9110, permanent] Theuser agent string of the user agent.
For example:User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20100101 Firefox/12.0
[RFC 9110, permanent] Ask the server to upgrade to another protocol. Must not be used in HTTP/2.[10]
For example:Upgrade: h2c, HTTPS/1.3, IRC/6.9, RTA/x11, websocket
[RFC 9110, permanent] Informs the server of proxies through which the request was sent.
For example:Via: 1.0 fred, 1.1 example.com (Apache/1.1)
[RFC 7234, 9111, obsolete] A warning about a possible problem with the entity body.[17] Since this header is often neither sent by servers nor acknowledged by clients, this header and its codes were obsoleted by the HTTP Working Group in 2022 withRFC 9111.[18]
The followingcaching related warning codes were specified under RFC 7234.[19][20]
For example:Warning: 199 Miscellaneous warning
Tells a server which (presumably in the middle of a HTTP -> HTTPS migration) hosts mixed content that the client would prefer redirection to HTTPS and can handleContent-Security-Policy: upgrade-insecure-requests[21]
For example:Upgrade-Insecure-Requests: 1
Mainly used to identifyAjax requests (mostJavaScript frameworks send this field with value ofXMLHttpRequest); also identifies Android apps using WebView[22]
For example: X-Requested-With: XMLHttpRequest
Requests a web application to disable their tracking of a user. This is Mozilla's version of the X-Do-Not-Track header field (sinceFirefox 4.0 Beta 11).Safari andIE9 also have support for this field.[23] On March 7, 2011, a draft proposal was submitted to IETF.[24] TheW3C Tracking Protection Working Group is producing a specification.[25][26]
For example:
DNT: 1 (Do Not Track Enabled)
DNT: 0 (Do Not Track Disabled)
Ade facto standard for identifying the originating IP address of a client connecting to a web server through an HTTP proxy or load balancer. Superseded byForwarded header.[27]
For example:X-Forwarded-For: client1, proxy1, proxy2X-Forwarded-For: 129.78.138.66, 129.78.64.103
Ade facto standard for identifying the original host requested by the client in theHost HTTP request header, since the host name and/or port of the reverse proxy (load balancer) may differ from the origin server handling the request. Superseded byForwarded header.[28]
For example:
X-Forwarded-Host: en.wikipedia.org:8080
X-Forwarded-Host: en.wikipedia.org
Ade facto standard for identifying the originating protocol of an HTTP request, since a reverse proxy (or a load balancer) may communicate with a web server using HTTP even if the request to the reverse proxy is HTTPS. An alternative form of the header (X-ProxyUser-Ip) is used by Google clients talking to Google servers. Superseded byForwarded header.[29]
For example:X-Forwarded-Proto: https
Non-standard header field used by Microsoft applications and load-balancers.[30]
For example:Front-End-Https: on
Requests a web application to override the method specified in the request (typically POST) with the method given in the header field (typically PUT or DELETE). This can be used when a user agent or firewall prevents PUT or DELETE methods from being sent directly (this is either a bug in the software component, which ought to be fixed, or an intentional configuration, in which case bypassing it may be the wrong thing to do).[31]
For example:X-HTTP-Method-Override: DELETE
Allows easier parsing of the MakeModel/Firmware that is usually found in the User-Agent String of AT&T Devices.[32]
For example:X-Att-Deviceid: GT-P7320/P7320XXLPG
Links to an XML file on the Internet with a full description and details about the device currently connecting. In the example to the right is an XML file for an AT&T Samsung Galaxy S2.[33]
For example:x-wap-profile:http://wap.samsungmobile.com/uaprof/SGH-I777.xml
Implemented as a misunderstanding of the HTTP specifications. Common because of mistakes in implementations of early HTTP versions. Has exactly the same functionality as standard Connection field. Must not be used with HTTP/2.[34][10]
For example:Proxy-Connection: keep-alive
Server-sidedeep packet inspection of a unique ID identifying customers ofVerizon Wireless; also known as "perma-cookie" or "supercookie".[35][36][37]
For example:X-UIDH: ...
Used to preventcross-site request forgery. Alternative header names are:X-CSRFToken[38] andX-XSRF-TOKEN[39].[40]
For example:X-Csrf-Token: i8XNjC4b8KVok4uw5RftR38Wgp2BFwql
Correlates HTTP requests between a client and server. Superseded by the traceparent header.[stackoverflow2 1][41][42][43][44]
For example:X-Request-ID: f058ebd6-02f7-4d3f-942e-904344e8cde5
The Save-Data client hint request header available in Chrome, Opera, and Yandex browsers lets developers deliver lighter, faster applications to users who opt-in to data saving mode in their browser.[45]
For example:Save-Data: on
The Sec-GPC (Global Privacy Control[broken anchor]) request header indicates whether the user consents to a website or service selling or sharing their personal information with third parties.[46]
For example:Sec-GPC: 1
This section lists header fields used in aresponse.
[RFC 8942, experimental] RequestsHTTP Client Hints.
For example:Accept-CH: UA, Platform
[RFC 7480, permanent] Specifying which web sites can participate incross-origin resource sharing.[6]
For example:Access-Control-Allow-Origin: *
[RFC 5789, permanent] Specifies which patch document formats this server supports.[47]
For example:Accept-Patch: text/example;charset=utf-8
[RFC 9110, permanent] What partial content range types this server supports viabyte serving.
For example:Accept-Ranges: bytes
[RFC 9111, permanent] The age the object has been in aproxy cache in seconds.
For example:Age: 12
[RFC 9110, permanent] Valid methods for a specified resource. To be used for a405 Method not allowed.
For example:Allow: GET, HEAD
[RFC 7838, permanent] A server uses "Alt-Svc" header (meaning Alternative Services) to indicate that its resources can also be accessed at a different network location (host or port) or using a different protocol. When using HTTP/2, servers should instead send an ALTSVC frame.[48]
For example:Alt-Svc: http/1.1="http2.example.com:8001"; ma=7200
[RFC 9111, permanent] Tells all caching mechanisms from server to client whether they may cache the response. A numeric value is in seconds.
If a web server responds withCache-Control: no-cache, then a web browser or othercaching system (intermediate proxies) must not use the response to satisfy subsequent requests without first checking with the originating server (this process is called validation). This header field is part of HTTP/1.1, and is ignored by some caches and browsers. It may be simulated by setting theExpires HTTP/1.0 header field value to a time earlier than the response time. Notice thatno-cache is not instructing the browser or proxies about whether or not to cache the content. It tells the browser and proxies to validate the cache content with the server before using it (this is done viaIf-Modified-Since,If-Unmodified-Since,If-Match, andIf-None-Match). Sending ano-cache value thus instructs a browser or proxy to not use the cache contents merely based on "freshness criteria" of the cache content. Another common way to prevent old content from being shown to the user without validation isCache-Control: max-age=0 which instructs the user agent that the content is stale and should be validated before use.
The valueno-store instructs a browser tonot cache the response, yet the browser is allowed to cache it none-the-less. In particular, the HTTP/1.1 definition draws a distinction between history stores and caches. If the user navigates back to a previous page, a browser may show a page that was stored on disk in the history store. This is correct behavior according to the specification. Many user agents provide different behavior in loading pages from the history store or cache depending on whether the protocol is HTTP or HTTPS.
For example:Cache-Control: max-age=3600
[RFC 9110, permanent] Control options for the current connection and list of hop-by-hop response fields.[9] Must not be used with HTTP/2.[10]
For example:Connection: close
[RFC 2616, 4021, 6266, permanent] An opportunity to raise a "File Download" dialogue box for a known MIME type with binary format or suggest a filename for dynamic content. Quotes are necessary with special characters.[49]
For example:Content-Disposition: attachment; filename="fname.ext"
[RFC 9110, permanent] The type of encoding used on the data. SeeHTTP compression.
For example:Content-Encoding: gzip
[RFC 9110, permanent] The natural language or languages of the intended audience for the enclosed content.[50]
For example:Content-Language: da
[RFC 9110, permanent] The length of the response body inoctets (8-bit bytes).
For example:Content-Length: 348
[RFC 9110, permanent] An alternate location for the returned data.
For example:Content-Location: /index.htm
[RFC 1544, 1864, 4021, obsolete] ABase64-encoded binaryMD5 sum of the content of the response.[11]
For example:Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ==
[RFC 9110, permanent] Where in a full body message this partial message belongs.
For example:Content-Range: bytes 21010-47021/47022
[RFC 9110, permanent] TheMIME type of this content.
For example:Content-Type: text/html; charset=utf-8
[RFC 9110, permanent] The date and time that the message was sent (in "HTTP-date" format as defined by RFC 9110).
For example:Date: Tue, 15 Nov 1994 08:12:31 GMT
[RFC 3229, permanent] Specifies the delta-encoding entity tag of the response.[5]
For example:Delta-Base: "abc"
[RFC 9110, permanent] An identifier for a specific version of a resource, often amessage digest.
For example:ETag: "737060cd8c284d8af7ad3082f209582d"
[RFC 9111, permanent] Gives the date/time after which the response is considered stale (in "HTTP-date" format as defined by RFC 9110).
For example:Expires: Thu, 01 Dec 1994 16:00:00 GMT
[RFC 3229, permanent] Instance-manipulations applied to the response.[5]
For example:IM: feed
[RFC 9110, permanent] The last modified date for the requested object (in "HTTP-date" format as defined by RFC 9110).
For example:Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
[RFC 8288, permanent] Used to express a typed relationship with another resource, where the relation type is defined by RFC 8288.[51]
For example:Link: </feed>; rel="alternate"
[RFC 9110, permanent] Used inredirection, or when a new resource has been created.
For example:Location: http://www.w3.org/pub/WWW/People.html
For example:Location: /pub/WWW/People.html
[RFC 2626, permanent] This field is supposed to setP3P policy, in the form ofP3P:CP="your_compact_policy". However, P3P did not take off,[52] most browsers have never fully implemented it; a lot of websites set this field with fake policy text, enough to fool browsers into thinking a P3P policy existed and granting permissions forthird party cookies.
For example:P3P: CP="This is not a P3P policy! See https://en.wikipedia.org/wiki/Special:CentralAutoLogin/P3P for more info."
[RFC 9111, permanent] Implementation-specific fields that may have various effects anywhere along the request-response chain.
For example:Pragma: no-cache
[RFC 7240, permanent] Indicates which Prefer tokens were honored by the server and applied to the processing of the request.
For example:Preference-Applied: return=representation
[RFC 9110, permanent] Request authentication to access the proxy.
For example:Proxy-Authenticate: Basic
[RFC 7469, permanent]HTTP Public Key Pinning, announces hash of website's authenticTLS certificate.[53]
For example:Public-Key-Pins: max-age=2592000; pin-sha256="E9CZ9INDbd+2eRQozYqqbQ2yXLVKB9+xcprMF+44U1g=";
[RFC 9110, permanent] If an entity is temporarily unavailable, this instructs the client to try again later. Value could be a specified period of time (in seconds) or a HTTP-date.[54]
For example 1:Retry-After: 120 For example 2:Retry-After: Fri, 07 Nov 2014 23:59:59 GMT
[RFC 9110, permanent] A name for the server.
For example:Server: Apache/2.4.1 (Unix)
[RFC 6265, permanent] AnHTTP cookie.
For example:Set-Cookie: CookieName=CookieValue; Max-Age=3600; Version=1
[RFC 6797, permanent] A HSTS Policy informing the HTTP client how long to cache the HTTPS-only policy and whether this applies to subdomains.
For example:Strict-Transport-Security: max-age=16070400; includeSubDomains
[RFC 9110, permanent] The Trailer general field value indicates that the given set of header fields is present in the trailer of a message encoded withchunked transfer coding.
For example:Trailer: Max-Forwards
[RFC 9110, permanent] The form of encoding used to safely transfer the entity to the user.Currently defined methods are:chunked, compress, deflate, gzip, identity. Must not be used with HTTP/2.[10]
For example:Transfer-Encoding: chunked
[RFC 2295, permanent] Tracking Status header, value suggested to be sent in response to a DNT (do-not-track) request. Possible values:
For example:Tk: ?
[RFC 9110, permanent] Ask the client to upgrade to another protocol. Must not be used in HTTP/2.[10]
For example:Upgrade: h2c, HTTPS/1.3, IRC/6.9, RTA/x11, websocket
[RFC 9110, permanent] Tells downstream proxies how to match future request headers to decide whether the cached response can be used rather than requesting a fresh one from the origin server.
For example 1:Vary: * For example 2:Vary: Accept-Language
[RFC 9110, permanent] Informs the client of proxies through which the response was sent.
For example:Via: 1.0 fred, 1.1 example.com (Apache/1.1)
[RFC 7234, RFC 9111, obsolete] A general warning about possible problems with the entity body.[17]
For example:Warning: 199 Miscellaneous warning
[RFC 9110, permanent] Indicates the authentication scheme that should be used to access the requested entity.
For example:WWW-Authenticate: Basic
[RFC 7034, obsolete]Clickjacking protection:deny - no rendering within a frame,sameorigin - no rendering if origin mismatch,allow-from - allow from specified location,allowall - non-standard, allow from any location.[55]
For example:X-Frame-Options: deny
Content Security Policy definition.[56]
For example:X-WebKit-CSP: default-src 'self'
Notify to prefer to enforceCertificate Transparency.[57]
For example:Expect-CT: max-age=604800, enforce, report-uri="https://example.example/report"
Used to configure network request logging.[58]
For example:NEL:{"report_to":"name_of_reporting_group","max_age":12345,"include_subdomains":false,"success_fraction":0.0,"failure_fraction":1.0}
To allow or disable different features or APIs of the browser.[59]
For example:Permissions-Policy: fullscreen=(), camera=(), microphone=(), geolocation=(), interest-cohort=()[60]
Tells the browser torefresh the page orredirect to a different URL, after a given number of seconds (0 meaning immediately);or when a new resource has been created[clarification needed]. Header introduced by Netscape in 1995 and became a de facto standard supported by most web browsers. Eventually standardized in the HTML Living Standard in 2017.[61]
For example:Refresh: 5; url=http://www.w3.org/pub/WWW/People.html
Instructs the user agent to store reporting endpoints for an origin.[62]
For example:Report-To:{"group":"csp-endpoint","max_age":10886400,"endpoints":[{"url":"https-url-of-site-which-collects-reports"}]}
CGI header field specifying thestatus of the HTTP response. Normal HTTP responses use a separate "Status-Line" instead, defined by RFC 9110.[63]
For example:Status: 200 OK
TheTiming-Allow-Origin response header specifies origins that are allowed to see values of attributes retrieved via features of theResource Timing API, which would otherwise be reported as zero due to cross-origin restrictions.[64]
For example:Timing-Allow-Origin: *Timing-Allow-Origin: <origin>[, <origin>]*
Provide the duration of the audio or video in seconds. Not supported by current browsers – the header was only supported by Gecko browsers, from which support was removed in 2015.[65][66]
For example:X-Content-Duration: 42.666
The only defined value, "nosniff", preventsInternet Explorer from MIME-sniffing a response away from the declared content-type. This also applies toGoogle Chrome, when downloading extensions.[67][68]
For example:X-Content-Type-Options: nosniff[69]
Specifies the technology (e.g. ASP.NET, PHP, JBoss) supporting the web application (version details are often inX-Runtime,X-Version, orX-AspNet-Version).[stackoverflow1 1]
For example:X-Powered-By: PHP/5.4.0
Specifies the component that is responsible for a particular redirect.[70]
For example:X-Redirect-By: WordPressX-Redirect-By: Polylang
Correlates HTTP requests between a client and server.[stackoverflow2 1]
For example:X-Request-ID: f058ebd6-02f7-4d3f-942e-904344e8cde5
Recommends the preferred rendering engine (often a backward-compatibility mode) to use to display the content. Also used to activateChrome Frame in Internet Explorer. In HTML Standard, only theIE=edge value is defined.[71][72]
For example:
X-UA-Compatible: IE=edgeX-UA-Compatible: IE=EmulateIE7X-UA-Compatible: Chrome=1
Cross-site scripting (XSS) filter[73]
For example:X-XSS-Protection: 1; mode=block
This article incorporates text available under theCC BY-SA 2.5 license.For meta elements with an http-equiv attribute in the X-UA-Compatible state, the content attribute must have a value that is an ASCII case-insensitive match for the string"IE=edge".As ofthis edit, this article uses content from"What is the X-REQUEST-ID http header?", authored byStefan Kögl at Stack Exchange, which is licensed in a way that permits reuse under theCreative Commons Attribution-ShareAlike 3.0 Unported License, but not under theGFDL. All relevant terms must be followed.
As ofthis edit, this article uses content from"Why does ASP.NET framework add the 'X-Powered-By:ASP.NET' HTTP Header in responses?", authored byAdrian Grigore at Stack Exchange, which is licensed in a way that permits reuse under theCreative Commons Attribution-ShareAlike 3.0 Unported License, but not under theGFDL. All relevant terms must be followed.