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Know your rel-tag






rel-tag uses a rel value of “tag” on a hyperlink element to “tag” or “label” the page, blog post, or other major part of the page it apears in. When a rel-tag link appears inside another microformat (for example in hAtom) it applies to that microformat, and not the page as a whole.

By adding a rel-tag link to a page (or other microformat) you make an assertion about what this page or part of it is about.


a rel-tag is a standard hyperlink element, with a rel value of (or including) “tag”. The href value points to an entry in a “tagspace”. A tagspace is a set of URLs of the form http://tagspaceURL/tagvalue, for example

  • uses wikipedia as a tagspace, and the value of this tag is “RSS”
  • htp:// uses technorati as a tagspace, but the value of this tag is identical to the previous – “RSS”

The actual value of the tag is the final segment of the url value, after the last “/” – meaning that the value of a tag is not dependent on the tagspace being pointed to. Should the last character be a slash (“/”) then this final slash is ignored when determining the tag value. A resource at the URL should exist.

Technorati and Wikipedia are common tagspaces, but anyone may implement their own tagspace.


<a href="" rel="tag">microformats</a> tags the page or major part of the page it is in as being about microformats.

<a href="" lang="it" rel="tag">cucina</a> tags the page or major part of the page it is in as being about cooking. This demonstrates how tagging works with internationalization – the human firendly language here is itaina, the language of the page in which it appears, but the tag value is “cooking” meaning that we can aggregate pages based on their tags despute being in different languages. Of course there is no reason why we could not mark this up like this

<a href="" lang="it" rel="tag">cucina</a>

But in this case, the value of the microformat is “cucina”. There is of course no requrement that tag values be English language words, but by using the English translation of a tag value, pages can be aggregateed on the basis of their content, despite their human language.

Tools for publishing rel-tag

For WordPress

For Textpattern

For Bloxsom

Tagging plugin from Axel Beckert


Drew McLellan’s WaSP Dreamweaver microformats extension also you to easily add tags to any web page you are working on

Services using rel-tag

Tag search

Technorati tag search indexes tagged blog posts and other content. Use Technorati’s ping to ensure technorati indexes your rel-tagged content –

Blog search engine Icerocket also allows for tag based searching. –


You can “validate” your rel-tags using the rel-lint tool from Drew McLellan –

Operator, from Michael Kaply, is an extension for Firefox 2, which extracts tag (and other microformatted) data from a page, and enables various actions on it. In debug mode it shows errors to help debug problems.


  • ODEO publishes user tags using rel-tag
  • Eventful publishes user tags using rel-tag
  • LiveJournal publishes user tags using rel-tag