[Build Backlinks Online] Rel=Confused? Answers to Your Rel=Canonical Questions

Build Backlinks Online has posted a new item, 'Rel=Confused? Answers to Your
Rel=Canonical Questions'


Posted by Dr. Pete

Its been over four years (February 2009) since Google and Yahoo announced
support for the rel=canonical tag, and yet this single line of HTML is still
causing a lot of confusion for SEOs and webmasters. Recently, Google posted 5
common mistakes with rel=canonical its a good post and a welcome bit of
transparency, but it doesnt address a lot of the questions we see daily here in
Q&A. So, I thought it was a good time to tackle some of your most common
questions (and please forgive the following nonsense)....



What Is Rel=Canonical?


Put simply, the rel=canonical tag is a way to tell Google that one URL is
equivalent to another URL, for search purposes. Typically, a URL (B) is a
duplicate of URL (A), and the canonical tag points to (A). The following tag
would appear on the page that generates URL (B), in the <head/head>:

<link rel=canonical href=http://www.example.com/url-a.html />

Googles support document on rel=canonical is actually pretty good. The subject
of duplicate content is complex, and Ive addressed it previously in detail. For
this post, Im going to skip ahead and assume that you have a working knowledge
of technical SEO and have attempted to use rel=canonical on your site.

Note: Rel=canonical is also referred to as Rel-canonical and The Canonical Tag.
For this article, I will try to consistently refer to it as Rel=canonical.

(1) Should I Use Rel=Canonical for Pagination?


Im not going to repeat all of Googles answers, but this one is so frequently
asked that it deserves more detail. Lets say you have a series of paginated
search results (1, 2, 3 n). These can be considered thin, from a search
standpoint, so should you rel=canonical page n back to page 1?

Officially, the answer is no Google does not recommend this. They recommend
that you either rel=canonical to a View All page (if having all results on one
page is viable) or that you use rel=prev/next. Rel=canonical can be used in
conjunction with rel=prev/next to handle search sorts, filters, etc., but that
gets complicated fast.

Pagination for SEO is a very tricky subject, and I recommend you check out
these two resources:


Conquering Pagination A Guide to Consolidating your Content


The Latest & Greatest On SEO Pagination



(2) Can I Use Rel=Canonical Cross-domain?


Yes in late 2009, Google announced support for cross-domain use of
rel=canonical. This is typically for syndicated content, when youre concerned
about duplication and only want one version of the content to be eligible for
ranking.

(3) Should I Use Rel=Canonical Cross-Domain?


Thats a tougher question. First off, Google may choose to ignore cross-domain
use of rel=canonical if the pages seem too different or it appears manipulative.
The ideal use of cross-domain rel=canonical would be a situation where multiple
sites owned by the same entity share content, and that content is useful to the
users of each individual site. In that case, you probably wouldnt want to use
301-redirects (it could confuse users and harm the individual brands), but you
may want to avoid duplicate content issues and control which property Google
displays in search results. I would not typically use rel=canonical cross-domain
just to consolidate PageRank.

(4) Should I Use Rel=Canonical on Near Duplicates?


As my catastrophic canonicalization experiment and follow-up experiments
showed, Google does honor rel=canonical even on very different pages, in some
cases. That doesnt mean that its a good idea. Generally speaking, I think its
best to reserve rel=canonical for duplicates or very-near duplicates. For
example, if a product pages spins off into five URLs for five different colors,
and each color's page only differs by a sentence or two (or an image), then yes,
I think its fine to rel=canonical to the parent product page.

Do not use rel=canonical as a substitute for appropriate 301-redirects and/or
404s. While it probably wont cause large-scale catastrophes, I strongly suspect
that Google will start to ignore your canonical tags, and this may impact how
you control legitimate duplicates.

(5) Can I Put Rel=Canonical on the Canonical Page?


In other words, is it alright to put a rel=canonical tag on the canonical
version of the URL, pointing back to itself? Practically speaking yes, it is,
but you don't have to. Early on, there were hints that both Google and Bing
preferred that you not overuse rel=canonical. Over time, though, their stances
seemed to soften, and Ive seen no evidence in recent history of a properly used,
self-referencing canonical causing any harm.

This is often just a practical issue many URLs share common templates, and the
code needed to display a rel=canonical tag on just the duplicates and not the
canonical version of a page can get messy and increase your chance of mistakes.
Personally, I believe that the search engines recognized the reality most
webmasters face and adjusted their initial, conservative stance.

(6) Is It OK to Put Rel=Canonical on My Entire Site?


Should you pre-emptively rel=canonical your entire site even if many of the
pages arent subject to duplicate content issues? I think this gets very
speculative. We have recommended this approach at SEOmoz in the past, and I
think its generally safe. I do worry that excessive use of rel=canonical could
cause search engines to devalue and even ignore those tags, but I cant point to
any clear evidence of this happening. I also worry that people often implement
site-wide rel=canonical tags badly, and end up pointing them to the wrong pages.

I do think that a pre-emptive rel=canonical on your home-page is generally a
good ideas, as home pages are prone to URL variations. In a perfect world, Id
say to use rel=canonical on the home-page, known duplicates, and any pages with
parameters that could drive duplicate content, and leave the rest alone.
However, thats often a very difficult procedure. In some cases, site-wide
rel=canonical implementation is better than no index control.

(7) Should I Use Rel=Canonical or 301 Redirects?


Please understand that while these two approaches can behave similarly, from an
SEO standpoint, they are not interchangeable. Heres the critical difference a
301-redirect takes the visitor to the canonical URL, while a rel=canonical tag
does not. Usually, only one of these approaches is the right one for your
visitors. If you really want to permanently consolidate two pages and remove the
duplicates, then use a 301-redirect. If you want to keep both pages available to
visitors, but only have one appear in search results, then use rel=canonical.

(8) Does Rel=Canonical Pass Authority/PageRank?

This is very difficult to measure, but if you use rel=canonical appropriately,
and if Google honors it, then it appears to act similarly to a 301-redirect. We
suspect it passes authority/PageRank for links to the non-canonical URL, with
some small amount of loss (similar to a 301).

(9) Can I Chain Rel=Canonicals (+301s, 302s, etc.)?

What happens if you rel=canonical to a URL with rel=canonical to another URL,
or you rel=canonical to a URL that 301-redirects to another URL? It gets
complicated. In some cases, it might work and it might even pass PageRank.
Generally speaking, though, its a bad idea. At best, its sloppy. At worst, it
might not function at all, or you might lose significant PageRank across the
chain. Wherever possible, avoid chains and implement rel=canonical in a single
hop.

(10) Are Non-Canonical Pages Indexed?


For all practical purposes no. If Google honors a rel=canonical tag, then the
non-canonical page is not eligible for ranking. It will not have a unique cached
copy, and it will not appear in the public index via a site: search. Now, does
Google maintain a record of the non-canonical URL? I assume they do. As an SEO,
though, the non-canonical URL ceases to exist in any meaningful way.

(11) Can Someone Else Rel=Canonical My Pages?


Ive seen occasional worries about someone using rel=canonical, especially
cross-domain, to harm a site or steal its authority. Keep in mind that you can
only grant canonical status from pages you control. So, you could rel=canonical
all of your pages to someone elses site, but why would anyone do that? To wreak
any real havoc, someone would have to hack into your site. If that happens, then
rel=canonical abuse is the least of your problems. The vast, vast majority of
damage done by rel=canonical is self-inflicted.

(12) Can I Have My Cake and Eat It, Too?


No. Yeah, I know you dont want to hear it. At least a third of the questions
we get about rel=canonical boil down to I want all of these pages to rank, and
theyre the same, but I dont want to get in any trouble for duplicate content! I
dont have any secret sauce to pour on that.

You dont have to use rel=canonical, but. in my experience. controlling your own
duplicate content is better than having Google do it for you, and eventually
theyll do it for you. In the old days, that might just mean that the wrong page
got filtered out. After 25+ Panda updates, though, it could mean that your
entire site suffers. You cant have it both ways if you have duplicate content,
then remove it, control it, or improve it.

What Questions Do You Have?


If you have any general questions about the canonical tag or how to use it,
feel free to leave a comment, and Ill try to address them. Please understand
that I cant dig into your site and provide consulting-level services, but if you
can ask the question in a general way that will be helpful to others, Ill do my
best to leave a reply.
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