LINK Tag, REL attribute and SEO – The Complete HTML Guide for Search Engine Optimization
Keep in mind that the REL attribute can be applied to an A tag too. This means that you can specify relationships between the interlinked documents not only in the head section of your web pages, but anywhere inside your documents.
The opposite of the REL attribute is the REV attribute and you can find a good explanation of both in here. For more values of the REL attribute here’s a comprehensive list. Keep in mind that the list of supported values for REL attribute is different for HTML 4 and HTML 5.
Why do you need to pay attention this attribute?
First, some search engines will use the LINK tag to discover other documents. To identify new documents they will try to crawl the URL provided in the HREF value of this tag. The relationship between the interlinked documents is specified in the REL attribute and the type of relationship can have very important consequences on how search engines crawl your website (think about the canonical value of the REL attribute or nofollow).
Second, some browsers may display navigational icons when they identify an RSS feed associated with the current document, which is great for usability and improving behavioral metrics such as page views or time on site:
Third, you can use this attribute to provide search engine additional information about the interlinked documents. For example you can specify the author of the linked document, which can help bots identify the original source of a content, even if it gets copied and republished over and over again. Google is now supporting the author value of the REL attribute and use it to determine the relevancy of one’s page to a user’s query. Here‘s the official document describing how you can use the author and me.
Should you worry about all values for this attribute?
No. There are tens of allowed values for rel, but in terms of SEO, I think you should pay attention to the following values:
canonical – the most important attribute, tells search engines which page should be indexed when there are duplicate or very similar versions of the same page across the same site (or even different websites). This attribute deserve an article on its own, but until I’ll write one please read the official guideline from Google. It’s important to know that canonical is passing PR just as with any other ordinary A links.
nofollow – this is the “no Page Rank juice” attribute and you should basically use it on all external links for which you don’t want to pass PR.
alternate AND hreflang – the alternate value becomes important when combined with HREFLANG, to unify content under multilingual templates. “If you translate only the template of your pages, such as the side navigation and footer, while keeping the bulk of your content in a single language (as often happens on pages featuring user-generated content), using REL=”alternate” HREFLANG=”x” along with REL=”canonical” or 301 redirects is a good technique to help Google serve the correct language URL to searchers” – excerpt from Google Webmaster Central. You should also read this article, which is also related to multiple languages on the same site.
author or me – author and me can be used to define relationships between a web document and its author(s). This can be used by search engines to determine the original author for duplicate content. The official document describing how you can use the author and me, can be found here. Briefly put, if you link to your profiles on any social network from other web documents, use the REL=”me” attribute to tell search engines that the linked page belongs to you and is your social profile.
tag – this value introduces us to the micro formats. By adding REL=”tag” to a hyperlink, a page indicates that the destination of that hyperlink is an author-designated “tag” (or keyword/subject) for the current page.
bookmark - The HTML4 spec describes a bookmark as “a link to a key entry point within an extended document”. By convention, this entry point also captures the notion of a “permalink”.
previous and next – these are used to suggest a series of documents related to each other (it can be an article split in multiple parts, multi-page categories on an ecommerce website, search result pages) and are used by Google to understand relationships between pages.
license – you can use this value for copyright attribution on your own images. Here’s how:
There are an impressive number of REL values for social networks (The XHTML Friends Network) but those are not (yet) so widely used or possibly not influencing rankings at this time. Some of them might be used by Google to establish relationships between social network accounts and even show up in the search results:
Bonus 1: did you know that you can actually alter the appearance of the links that contain the REL attribute, such as adding a specific icon for each value of the attribute? Here‘s a tutorial on how to do it.
Bonus 2: in case you want to specify a canonical version for documents which really don’t generate an html code (i.e. pdf documents), Google is now supporting REL=”canonical” in HTTP Headers.
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