Monday, April 08, 2013
Webmaster Level: Intermediate to Advanced
in your webpage is a strong hint to search engines your about preferred version to index among
duplicate pages on the web.
It's supported by several search engines, including
and Google. The
rel=canonical link consolidates indexing properties from the
duplicates, like their inbound links, as well as specifies which URL you'd like displayed in
search results. However,
rel=canonical can be a bit tricky because it's not very
obvious when there's a misconfiguration.
While the webmaster sees the "red velvet" page on the left in their browser, search engines notice
on the webmaster's unintended "blue velvet"
rel=canonical on the right. We recommend
the following best practices for using
- A large portion of the duplicate page's content should be present on the canonical version.
Double-check that your
rel=canonicaltarget exists (it's not an error or "
rel=canonicaltarget doesn't contain a noindex robots meta tag.
Make sure you'd prefer the
rel=canonicalURL to be displayed in search results (rather than the duplicate URL).
rel=canonicallink in either the
<head>of the page or the HTTP header.
Specify no more than one
rel=canonicalfor a page. When more than one is specified, all
rel=canonicallinks will be ignored.
rel=canonical to the first page of a paginated series
Imagine that you have an article that spans several pages:
- and so on
rel=canonical from page 2 (or any later page) to page 1 is not correct
rel=canonical, as these are not duplicate pages. Using
rel=canonical in this instance would result in the content on pages 2 and beyond not
being indexed at all.
Mistake 2: Absolute URLs mistakenly written as relative URLs
<link> tag, like many HTML tags, accepts both relative and absolute URLs.
Relative URLs include a path "relative" to the current page. For example,
images/cupcake.png means "from the current directory go to the
subdirectory, then to
cupcake.png." Absolute URLs specify the full path—including the
<link rel=canonical href="example.com/cupcake.html" /> (a relative
URL since there's no
http://) implies that the desired canonical URL is
http://example.com/example.com/cupcake.html even though that is
almost certainly not what was intended. In these cases, our algorithms may ignore the specified
rel=canonical. Ultimately this means that whatever you had hoped to accomplish with
rel=canonical will not come to fruition.
Mistake 3: Unintended or multiple declarations of
Occasionally, we see
rel=canonical designations that we believe are unintentional. In
very rare circumstances we see simple typos, but more commonly a busy site owner copies a page
template without thinking to change the target of the
rel=canonical. Now the site
owner's pages specify a
rel=canonical to the template author's site.
If you use a template, check that you didn't also copy the
Another issue is when pages include multiple
rel=canonical links to different URLs.
This happens frequently in conjunction with SEO plugins that often insert a default
rel=canonical link, possibly unbeknownst to the webmaster who installed the plugin.
In cases of multiple declarations of
rel=canonical, Google will likely ignore all the
rel=canonical hints. Any benefit that a legitimate
have offered will be lost.
In both these types of cases, double-checking the page's source code will help correct the issue.
Be sure to check the entire
<head> section as the
links may be spread apart.
Check the behavior of plugins by looking at the page's source code.
Mistake 4: Category or landing page specifies
rel=canonical to a featured article
Let's say you run a site about desserts. Your dessert site has useful category pages like
"pastry" and "gelato." Each day the category pages feature a unique article. For instance,
your pastry landing page might feature "red velvet cupcakes." Because the "pastry" category
page has nearly all the same content as the "red velvet cupcake" page, you add a
rel=canonical from the category page to the featured individual article.
If we were to accept this
rel=canonical, then your pastry category page would not
appear in search results. That's because the
rel=canonical signals that you would
prefer search engines display the canonical URL in place of the duplicate. However, if you want
users to be able to find both the category page and featured article, it's best to only have a
rel=canonical on the category page, or none at all.
Remember that the canonical designation also implies the preferred display URL. Avoid adding a
rel=canonical from a category or landing page to a featured article.
rel=canonical in the
rel=canonical link tag should only appear in the
<head> of an
HTML document. Additionally, to avoid HTML parsing issues, it's good to include the
rel=canonical as early as possible in the
<head>. When we
rel=canonical designation in the
This is an easy mistake to correct. Simply double-check that your
are always in the
<head> of your page, and as early as possible if you can.
rel=canonical designations in the
<head> are processed, not the
To create valuable
- Verify that most of the main text content of a duplicate page also appears in the canonical page.
rel=canonicalis only specified once (if at all) and in the
<head>of the page.
rel=canonicalpoints to an existent URL with good content (that is, not a
404, or worse, a
rel=canonicalfrom landing or category pages to featured articles as that will make the featured article the preferred URL in search results.
And, as always, please ask any questions in our Webmaster Help forum.