2600:8807:8882:6300:3597:D8A9:8CD1:98A5 at 05:04, 9 March 2025

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{{Short description|HTTP header field}}
{{HTTP}}
In [[Hypertext Transfer Protocol|HTTP]], "'''{{Not a typo|Referer}}'''" (a misspelling of "'''Referrer'''"<ref name="s3T5A" />) is an optional HTTP header field that identifies the address of the [[web page]] (i.e., the [[Uniform Resource Identifier|URI]] or [[Internationalized Resource Identifier|IRI]]) from which the resource has been requested. By checking the referrer, the server providing the new web page can see where the request originated.

In the most common situation, this means that when a user clicks a [[hyperlink]] in a [[web browser]], causing the browser to send a request to the server holding the destination web page, the request may include the {{Not a typo|Referer}} field, which indicates the last page the user was on (the one where they clicked the link).

[[website|Web sites]] and [[web server]]s [[Server log|log]] the content of the received {{Not a typo|Referer}} field to identify the web page from which the user followed a link, for promotional or statistical purposes.{{cn|date=November 2024}} This entails a loss of [[Information privacy|privacy]] for the user and may introduce a [[security]] risk.<ref name="Leak" /> To mitigate security risks, browsers have been steadily reducing the amount of information sent in Referer. As of March 2021, by default [[Google Chrome|Chrome]],<ref name="N9xNj" /> [[Chromium (web browser)|Chromium]]-based [[Microsoft Edge|Edge]], [[Firefox]],<ref name="6l6dr" /> [[Safari (web browser)|Safari]]<ref>{{Cite web|url=https://webkit.org/blog/9661/preventing-tracking-prevention-tracking/|title=Preventing Tracking Prevention Tracking|first=John|last=Wilander|website=WebKit blog|date=December 10, 2019|df=ymd}}</ref> default to sending only the origin in cross-origin requests, stripping out everything but the domain name.

== Etymology ==
The misspelling of ''[[wikt:referrer|referrer]]'' was introduced in the original proposal by computer scientist [[Phillip Hallam-Baker]] to incorporate the {{not typo|"Referer"}} header field into the [[HTTP]] specification.<ref name="hallam-baker" /><ref name="hallam-baker-2" /> The misspelling was set in stone by the time (May 1996) of its incorporation into the [[Request for Comments]] standards document RFC 1945<ref name="rfc1945" /> (which 'reflects common usage of the protocol referred to as "HTTP/1.0{{"'}} at that time); document co-author [[Roy Fielding]] remarked in March 1995 that "neither one ({{not typo|referer}} or referrer) is understood by" the standard [[Spell (Unix)|Unix spell checker]] of the period.<ref name="fielding" /> {{not typo|"Referer"}} has since become a widely used spelling in the industry when discussing HTTP referrers; usage of the misspelling is not universal, though, as the correct spelling "referrer" is used in some web specifications such as the <code>Referrer-Policy</code> HTTP header or the [[Document Object Model]].<ref name="Leak" />

== Details ==
When visiting a web page, the referrer or referring page is the URL of the previous web page from which a link was followed.

More generally, a referrer is the URL of a previous item which led to this request. For example, the referrer for an image is generally the [[HTML]] page on which it is to be displayed. The referrer field is an optional part of the HTTP request sent by the [[web browser]] to the web server.<ref name="acQA3" />

Many websites log referrers as part of their attempt to [[web tracking|track their users]]. Most [[web log analysis software]] can process this information. Because referrer information can violate [[privacy]], some web browsers allow the user to disable the sending of referrer information.<ref name="sendRefererHeader" /> Some [[Proxy server|proxy]] and [[firewall (networking)|firewall]] software will also filter out referrer information, to avoid leaking the location of non-public websites. This can, in turn, cause problems: some web servers block parts of their website to web browsers that do not send the right referrer information, in an attempt to prevent [[deep linking]] or unauthorised use of images ([[bandwidth theft]]). Some proxy software has the ability to give the top-level address of the target website as the referrer, which reduces these problems but can still in some cases divulge the user's last-visited web page.

Many blogs publish referrer information in order to link back to people who are linking to them, and hence broaden the conversation. This has led, in turn, to the rise of [[referrer spam]]: the sending of fake referrer information in order to popularize the spammer's website.

It is possible to access the referrer information on the client side using document.referrer in [[JavaScript]].<ref name="document.referrer" /> This can be used, for example, to individualize a web page based on a user's search engine query. However, the referrer field does not always include search keywords, such as when using [[Google Search]] with HTTPS.<ref name="wjfXX" />

== {{anchor|Referrer hiding}} Referrer hiding ==
Most web servers maintain logs of all traffic, and record the HTTP referrer sent by the web browser for each request. This raises a number of privacy concerns, and as a result, a number of systems to prevent web servers being sent the real referring URL have been developed. These systems work either by blanking the referrer field or by replacing it with inaccurate data. Generally, [[Internet security|Internet-security]] suites blank the referrer data, while web-based servers replace it with a false URL, usually their own. This raises the problem of referrer spam. The technical details of both methods are fairly consistent – software applications act as a [[proxy server]] and manipulate the HTTP request, while web-based methods load websites within frames, causing the web browser to send a referrer URL of their website address. Some web browsers give their users the option to turn off referrer fields in the request header.<ref name="sendRefererHeader" />

Most web browsers do not send the referrer field when they are instructed to redirect using the "Refresh" field. This does not include some versions of [[Opera (web browser)|Opera]] and many mobile web browsers. However, this method of redirection is discouraged by the [[World Wide Web Consortium]] (W3C).<ref name="tt75N" />

If a website is accessed from a [[HTTP Secure]] (HTTPS) connection and a link points to anywhere except another secure location, then the referrer field is not sent.<ref name="acQA3" />

The [[HTML5]] standard added support for the attribute/value <code>rel="noreferrer"</code>, which instructs the user agent to not send a referrer.<ref name="IO0P3" />

Another referrer hiding method is to convert the original link URL to a [[Data URI scheme]]-based URL containing small HTML page with a [[meta refresh]] to the original URL. When the user is redirected from the <code>data:</code> page, the original referrer is hidden.

[[Content Security Policy]] standard version 1.1 introduced a new ''referrer'' directive that allows more control over the browser's behaviour in regards to the referrer header. Specifically it allows the webmaster to instruct the browser not to block referrer at all, reveal it only when moving with the same origin etc.<ref name="kmzCq" />

== References ==
{{reflist|1=30em|refs=
<ref name="Leak">{{cite news |date=2015-09-16 |title=Does your website have a leak? |work=ICO Blog |url=https://iconewsblog.org.uk/2015/09/16/does-your-website-have-a-leak/ |access-date=2018-08-16 |url-status=dead |archive-url=http://webarchive.nationalarchives.gov.uk/20180524163908/https://iconewsblog.org.uk/2015/09/16/does-your-website-have-a-leak/ |archive-date=2018-05-24 }}</ref>
<ref name="hallam-baker">{{cite newsgroup| url=https://groups.google.com/group/alt.folklore.computers/msg/e17f380d477d0526?dmode=source | title=Re: Is Al Gore The Father of the Internet? | last=Hallam-Baker | first=Phillip | date=2000-09-21 | newsgroup=alt.folklore.computers | access-date=2013-03-20}}</ref>
<ref name="fielding">{{cite mailing list| url=http://lists.w3.org/Archives/Public/ietf-http-wg-old/1995JanApr/0107.html | title=Re: referer: (sic) | last=Fielding | first=Roy | author-link=Roy Fielding | mailing-list=ietf-http-wg-old | date=1995-03-09 | access-date=2013-03-20}}</ref>
<ref name="hallam-baker-2">{{cite web |last1=Hallam-Baker |first1=Phillip |title=Re: Referer: (sic) |url=https://lists.w3.org/Archives/Public/ietf-http-wg/1995JanMar/0109.html |website=W3C Public mailing list archives |access-date=19 February 2024 |url-status=live |archive-url=https://web.archive.org/web/20240219202530/https://lists.w3.org/Archives/Public/ietf-http-wg/1995JanMar/0109.html |archive-date=2024-02-19 }}</ref>
<ref name="sendRefererHeader">{{cite web | url=http://kb.mozillazine.org/Network.http.sendRefererHeader | title=Network.http.sendRefererHeader | date=2007-06-10 | publisher=[[MozillaZine]] | access-date=2015-05-27}}</ref>
<ref name="document.referrer">{{cite web | url=http://w3schools.com/jsref/prop_doc_referrer.asp | title=HTML DOM Document referrer Property | publisher=W3Schools | access-date=2013-03-20}}</ref>
<ref name="s3T5A">{{cite book|url=https://books.google.com/books?id=3EybAgAAQBAJ&pg=PT541|title=HTTP:The Definitive Guide|isbn=9781565925090|last1=Gourley|first1=David|last2=Totty|first2=Brian|last3=Sayer|first3=Marjorie|last4=Aggarwal|first4=Anshu|last5=Reddy|first5=Sailu|date=27 September 2002|publisher="O'Reilly Media, Inc." }}</ref>
<ref name="N9xNj">{{Cite web|title=Referrer Policy: Default to strict-origin-when-cross-origin - Chrome Platform Status|url=https://www.chromestatus.com/feature/6251880185331712|access-date=2021-03-23|website=www.chromestatus.com}}</ref>
<ref name="6l6dr">{{Cite web|last1=Lee|first1=Dimi|last2=Kerschbaumer|first2=Christoph|title=Firefox 87 trims HTTP Referrers by default to protect user privacy|url=https://blog.mozilla.org/security/2021/03/22/firefox-87-trims-http-referrers-by-default-to-protect-user-privacy|access-date=2021-03-23|website=Mozilla Security Blog|date=22 March 2021 |language=en-US}}</ref>
<ref name="wjfXX">{{cite web | url=https://blog.adobe.com/en/publish/2011/10/19/the-impact-of-google-encrypted-search | title=The Impact of Google Encrypted Search | last=Gundersen | first=Bret | date=2011-10-19 | publisher=[[Adobe Systems|Adobe Digital Marketing Blog]] | access-date=2021-03-17}}</ref>
<ref name="tt75N">{{cite web | url=http://www.w3.org/TR/WCAG10-HTML-TECHS/#meta-element | title=HTML Techniques for Web Content Accessibility Guidelines 1.0: The META element | date=2000-11-06 | publisher=[[W3C]] | access-date=2013-03-20}}</ref>
<ref name="acQA3">{{cite IETF| rfc=7231 |section=5.5.2 | title=Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content: referrer (RFC 7231 § 5.5.2) | date=June 2014 | publisher=IETF | doi=10.17487/RFC7231 | access-date=2014-07-26| editor-last1=Fielding | editor-last2=Reschke | editor-first1=R. | editor-first2=J. | last1=Fielding | first1=R. | last2=Reschke | first2=J. | s2cid=14399078 }}</ref>
<ref name="IO0P3">{{cite web | url=https://www.whatwg.org/specs/web-apps/current-work/multipage/links.html#link-type-noreferrer | title=4.12 Links — HTML Living Standard: 4.12.5.8 Link type "noreferrer" | date=2016-02-19 | publisher=[[WHATWG]] | access-date=2016-02-19}}</ref>
<ref name="kmzCq">{{cite web | url=http://www.w3.org/TR/CSP11/#directive-referrer | title=Content Security Policy Level 2 | publisher=W3 | date=2014 | access-date=2014-12-08}}</ref>
<ref name="rfc1945">{{cite IETF | title = Hypertext Transfer Protocol -- HTTP/1.0 | rfc = 1945 | first1 = T. | last1 = Berners-Lee | authorlink1 = Tim Berners-Lee | first2 = R. | last2 = Fielding | authorlink2 = Roy Fielding | first3 = H. | last3 = Frystyk | authorlink3 = Henrik Frystyk Nielsen | date=May 1996 | publisher = [[Internet Engineering Task Force|IETF]] | doi = 10.17487/RFC1945 }}</ref>
}}
==External links==
{{Wiktionary|referer|referrer}}
* {{IETF RFC|1945|link=no}}: Hypertext Transfer Protocol -- HTTP/1.0
* {{IETF RFC|7231|link=no}}: Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content
* {{IETF RFC|3987|link=no}}: Internationalized Resource Identifiers (IRIs)
* [//w3c.github.io/webappsec/specs/referrer-policy/ Referrer Policy - W3C Editor's Draft]

[[Category:URI schemes]]
[[Category:URL]]
[[Category:Hypertext Transfer Protocol headers]]
[[Category:Nonstandard spelling]]

HTTP referer - Revision history

2600:8807:8882:6300:3597:D8A9:8CD1:98A5 at 05:04, 9 March 2025