3 Reasons to use rel=canonical, and 4 reasons not to.
February 12, 2009 by ian
The major search engines just announced that they're going to start supporting a new link attribute: 'rel="canonical"'.
The Google Webmaster Central blog has a fair amount of detail, so I won't explain it all here.
A very brief lesson in canonicalization
Marcelo rightly pointed out a quick refresher might be in order. Here's what a canonicalization problem is:
Say you have a big web site with lots of pages. On most pages, you link to one critical article at:
http://www.mysite.com/index.cfm?artid=123
But, on a few pages, you linked to the same page using a slightly different URL:
http://www.mysite.com/index.cfm?artid=123&this=that
That difference is a canonical difference between the URLs.
You and I know perfectly well they're the same page. But a search engine does not. So they cheerfully crawl your site, splitting link authority and relevance between the two URLs and Ralph Naderizing (or Ross Peroing) your link building efforts.
Mixing home page links between www.mysite.com, mysite.com and www.mysite.com/index.cfm can have the same effect.
It's a major SEO bugaboo - my company has invested a lot of time and money in building a toolset just to sniff out these problems. So finding the problems aren't that hard. Fixing them is another matter entirely, because:
- When you go to your development team and ask them to fix canonicalization issues, they start sticking pins in voodoo dolls.
- Other sites may link to you using canonically inconsistent URLs. It's even harder to get them to change.
- Tracking down all the link sources is a major pain.
So, the new rel=canonical tag could save us a lot of pain.
Or not. Read on to get my two sides of the argument: To use, or not to use.
Reasons not to use the new canonicalization standard
But, ever the skeptic, I have a few things I think you should consider before diving into rel=canonical:
- Google doesn't offer unconditional support. Google says they will "take your preference into account" and that "it is a hint they will honor strongly". So rel=canonical is not a directive.
- Standards? We don't need no stinkin' standards. To this day, Google, Yahoo! and Live each support rel=nofollow in different ways. Compared to rel=canonical, nofollow was a cinch. Implementation is bound to be messy, at least until Google grinds its competitors into goo.
- You should've done it right the first time. You hear me. Why the hell do people still tack session id's, random URL variables and other crap onto URLs in this day and age? I don't know. But relying on someone else to fix the mess for you could be trouble.
- You're paranoid. If you're afraid the Search Engines Are Out To Get You, then you may not want to hand over even more information about your site's structure and your intentions.
But At Least We Have Options
That said, I'm pretty damned happy about rel=canonical. It gives me an option on sites where their canonicalization looks like a bowl of dried spaghetti.
So, use rel=canonical if:
- You have no other choice. Maybe you inherited an awful CMS implementation. Maybe you don't know how to code. Maybe your IT department just hates you. Rel=canonical lets you fix the problem with a simple <head> tag.
- It's impossible to track down all the incorrect link sources. If you have an old, established site with thousands of internal and external links all using different canonical URLs, then rel=canonical is a relatively painless fix that you can put in place on the target page. You no longer have to track down every link source.
- You want to try it. It can't hurt, right? (unless you're paranoid - see above)
I'll be testing out the new canonicalization tag in the coming weeks, and will let you know how it goes.
PS: I just posted a list of questions about rel=canonicalization. Go add to the list, please.
Join the Conversation:
Marcelo Calbucci says:
February 12, 2009 15:48
Hey, it would have been nice if you had a short paragraph explaining what the heck rel=canonical is for.
I know you live inside the SEO world, but I mostly get my SEO "news" from you. Unless you tell me what this is for I'll have to spend time and figure out somewhere else.
Cheers!
Ian
says:
February 12, 2009 16:11
Good point. I just added it above.
diane says:
February 13, 2009 17:11
Marcelo, rel=canonical is designed to determine whether your monastery is kosher per Canon Law. Isn't it obvious? ;)
Diane, born without a left brain
Ian
says:
February 14, 2009 09:18
@Diane you've out-hebed me. I didn't think that was possible.
diane says:
February 16, 2009 08:47
That's only because I've been listening to my CD of *Guys and Dolls* so much lately that I've turned into a female Nathan Detroit. You object? So...sue me, sue me, what can you do me?
Dena says:
April 15, 2010 05:55
Well Ian, i found this article when i was searching what the hell is rel=canonical for. And as i see from most sources, rel=canonical is useful for duplicate content. But i personally prefer sculpting different pages with nofollow. But canonical seems pretty useful when you can't get a track of nofollows :)
Ian
says:
April 15, 2010 06:45
@Dena I'd be careful about nofollow - it's changed quite a bit and doesn't sculpt the way most SEO's thought. Nofollow 'evaporates' pagerank, instead of funneling it...
Jon says:
April 21, 2010 02:15
"Nofollow 'evaporates' pagerank, instead of funneling it..."
Ian, can you expand a little bit please ( I understand the sculpting/funelling arguments )
Recently the google bot has been 'cleverer' and following a lot more parameterised links on my website-upshot is google webmaster 'links to site' pages have lots more of the these internal URLs. They are to pages which are not significant to my SEO goals ( eg to URLS that record a shorlisted item etc ) , so I have just added rel='nofollow' if for no other reason than to get these URLs out of my google WEBMASTER link listings.
Is this a mistake in the making and should I remove the nofollow?
Ian
says:
April 23, 2010 09:58
@Jon Don't use nofollow. It reduces the authority of the page on which you use it, as well as the target page. If you want to change your sitelinks, use the sitelinks tool in Google Webmaster Tools. If you want to remove links from your nav to improve pagerank funneling, you'll want to actually rearrange the links.
Zankhana says:
June 6, 2010 22:32
If I don't want search engines to follow some of my pages isn't it good to list those pages under Disallow in the robots.txt?