A major problem for search engines is to determine the original source for documents that are available on multiple URLs. Content duplication can happen in many ways, including:[3]
Duplication due to accessibility on different hosts/protocols
Duplication due to print versions of websites
Duplicate content issues occur when the same content is accessible from multiple URLs.[4] For example, http://www.example.com/page.html would be considered by search engines to be an entirely different page from http://www.example.com/page.html?parameter=1, even though both URLs may reference the same content.[5][6]
In February 2009, Google, Yahoo and Microsoft announced support for the canonical link element, which can be inserted into the <head> section of a web page, to allow webmasters to prevent these issues.[7] The canonical link element helps webmasters make clear to the search engines which page should be credited as the original.
Search engines try to utilize canonical link definitions as an output filter for their search results. If multiple URLs contain the same content in the result set, the canonical link URL definitions will likely be incorporated to determine the original source of the content. "For example, when Google finds identical content instances, it decides to show one of them. Its choice of the resource to display in the search results will depend upon the search query."[8][citation needed]
According to Google, the canonical link element is not considered to be a directive, but rather a hint that the ranking algorithm will "honor strongly."[1][9]
While the canonical link element has its benefits, Matt Cutts, then the head of Google's webspam team, has said that the search engine prefers the use of 301 redirects. Cutts said the preference for redirects is because Google's spiders can choose to ignore a canonical link element if they deem it more beneficial to do so.[10]
Implementationedit
Semantic tagedit
The canonical link element can be either used in the semantic HTML <head> or sent with the HTTP header of a document. For non HTML documents, the HTTP header is an alternate way to set a canonical URL.[3][11]
By the HTML 5 standard, the <linkrel="canonical"href="http://example.com/"> HTML element must be within the <head> section of the document.[12]
Self-hyperlinkedit
Some sites such as Stack Overflow[13] have on-page hyperlinks which link to a clean URL of themselves. Usability benefits are facilitating copying the hyperlink target URL or title if the browser or a browser extension offers a "Copy link text" context menu option for hyperlinks, the ability for the original URL to be retrieved from a saved page if not stored by the browser into a comment inside the file, as well as the ability to duplicate the opened page into a new tab right next to the currently opened one if the browser lacks such a feature.[14][13]
Examplesedit
HTMLedit
Below is an example of HTML code that uses the rel=canonical inside the <head> tag. The code could be used on a page, such as https://example.com/page.php?parameter=1to tell search engines that the https://example.com/page.php is the preferred version of the webpage.
^Biswas, Kushal. . RevenueI. Archived from the original on 14 June 2016. Retrieved 18 June 2015.
^Zadro, Dario (19 February 2015). "Rel=Canonical - A Beginners Guide to Canonical Tags - Where and When to Use Them". Zadro Web. Retrieved 18 June 2015.
^Fox, Vanessa (2009-02-12). "Google, Yahoo & Microsoft Unite On "Canonical Tag" To Reduce Duplicate Content Clutter". Search Engine Land. Retrieved 2012-08-02.
^"HTML link tag". www.w3schools.com. Retrieved 2019-01-07.
^ ab"Why does the question title link to itself on the answer page?". Meta Stack Exchange. 2010-04-23.
^"3 FireFox Addons to Easier Copy Links and Anchor Texts". Search Engine Journal. 7 January 2011.
December 18, 2023
canonical, link, element, canonical, link, element, html, element, that, helps, webmasters, prevent, duplicate, content, issues, search, engine, optimization, specifying, canonical, preferred, version, page, described, 6596, which, went, live, april, 2012, con. A canonical link element is an HTML element that helps webmasters prevent duplicate content issues in search engine optimization by specifying the canonical or preferred version of a web page It is described in RFC 6596 which went live in April 2012 1 2 Contents 1 Purpose 2 How search engines handle rel canonical 3 Implementation 3 1 Semantic tag 3 2 Self hyperlink 4 Examples 4 1 HTML 4 2 HTTP 5 See also 6 ReferencesPurpose editA major problem for search engines is to determine the original source for documents that are available on multiple URLs Content duplication can happen in many ways including 3 Duplication due to GET parameters Duplication with multiple URLs due to CMS Duplication due to accessibility on different hosts protocols Duplication due to print versions of websitesDuplicate content issues occur when the same content is accessible from multiple URLs 4 For example http www example com page html would be considered by search engines to be an entirely different page from http www example com page html parameter 1 even though both URLs may reference the same content 5 6 In February 2009 Google Yahoo and Microsoft announced support for the canonical link element which can be inserted into the lt head gt section of a web page to allow webmasters to prevent these issues 7 The canonical link element helps webmasters make clear to the search engines which page should be credited as the original How search engines handle a href Link relation html title Link relation rel a canonical editSearch engines try to utilize canonical link definitions as an output filter for their search results If multiple URLs contain the same content in the result set the canonical link URL definitions will likely be incorporated to determine the original source of the content For example when Google finds identical content instances it decides to show one of them Its choice of the resource to display in the search results will depend upon the search query 8 citation needed According to Google the canonical link element is not considered to be a directive but rather a hint that the ranking algorithm will honor strongly 1 9 While the canonical link element has its benefits Matt Cutts then the head of Google s webspam team has said that the search engine prefers the use of 301 redirects Cutts said the preference for redirects is because Google s spiders can choose to ignore a canonical link element if they deem it more beneficial to do so 10 Implementation editSemantic tag edit The canonical link element can be either used in the semantic HTML lt head gt or sent with the HTTP header of a document For non HTML documents the HTTP header is an alternate way to set a canonical URL 3 11 By the HTML 5 standard the span class p lt span span class nt link span span class na rel span span class o span span class s canonical span span class na href span span class o span span class s http example com span span class p gt span HTML element must be within the lt head gt section of the document 12 Self hyperlink edit Some sites such as Stack Overflow 13 have on page hyperlinks which link to a clean URL of themselves Usability benefits are facilitating copying the hyperlink target URL or title if the browser or a browser extension offers a Copy link text context menu option for hyperlinks the ability for the original URL to be retrieved from a saved page if not stored by the browser into a comment inside the file as well as the ability to duplicate the opened page into a new tab right next to the currently opened one if the browser lacks such a feature 14 13 Examples editHTML editBelow is an example of HTML code that uses the rel canonical inside the lt head gt tag The code could be used on a page such as https example com page php parameter 1to tell search engines that the https example com page php is the preferred version of the webpage lt DOCTYPE html gt lt html gt lt head gt lt link rel canonical href https www example com page php gt lt head gt lt body gt lt body gt lt html gt HTTP edit HTTP 1 1 200 OK Content Type application pdf Link lt https www newthink life page php gt rel canonical Content Length 4223 See also editURL normalizationReferences edit a b Kupke Joachim 2009 02 12 Specify your canonical Google Retrieved 2012 08 02 Cutts Matt 2009 02 15 Learn about the Canonical Link Element in 5 minutes Retrieved 2012 08 02 a b Link rel canonical How to do URL canonicalization right Audisto GmbH Retrieved 2015 10 06 Duplicate content Google Retrieved 2012 08 02 Biswas Kushal Canonical Issue and How to Use Canonical Tag The Proper Way RevenueI Archived from the original on 14 June 2016 Retrieved 18 June 2015 Zadro Dario 19 February 2015 Rel Canonical A Beginners Guide to Canonical Tags Where and When to Use Them Zadro Web Retrieved 18 June 2015 Fox Vanessa 2009 02 12 Google Yahoo amp Microsoft Unite On Canonical Tag To Reduce Duplicate Content Clutter Search Engine Land Retrieved 2012 08 02 How Google And Other Search Engines Manage Canonical Links http seomediax com seo how google and other search engines manage canonical links Consolidate duplicate URLs Search Console Help support google com Cutts Matt 2011 05 16 A rel equals canonical corner case Retrieved 2012 08 02 Consolidate duplicate URLs Search Console Help support google com HTML link tag www w3schools com Retrieved 2019 01 07 a b Why does the question title link to itself on the answer page Meta Stack Exchange 2010 04 23 3 FireFox Addons to Easier Copy Links and Anchor Texts Search Engine Journal 7 January 2011 Retrieved from https en wikipedia org w index php title Canonical link element amp oldid 1189374650, wikipedia, wiki, book, books, library,
