I messed up my canonical tags yesterday -- be careful

[deadsea]

I've had canonical tags on my todo list for a while. Yesterday I got around to implementing them. I applied them on my top three templates. I was trying to be very careful not to make any mistakes. I tested all the combinations I could think of.

Naturally, I messed something up. I forgot about the various languages the site is in. I canonicalized all the other languages to the English site. Oops. It was like that for about 24 hours. I hope googlebot didn't notice too much and that traffic to the international sites doesn't take a hit.

[tedster]

Thanks - that's an important caution. See Why Are There "Canonical Disasters" [webmasterworld.com] for other accounts of extended ranking problems after messing up with canonical link tags.

I haven't heard of extended problems recently, so it's possible Google is now able to fix things quicker if you fix things quickly. But it's not an area to mess around with.

[maximillianos]

I think you are okay if it has only been 24 hrs. Of course it depends on the size of your site, and how often G crawls your pages, but typically they take canonical tags as a suggestion. They are aware folks may make mistakes with it.

Of course they said that about on-site duplicate content years ago... and we all know what happened earlier this year. =)

[tedster]

typically they take canonical tags as a suggestion

Here's the exact wording:

Is rel="canonical" a hint or a directive?
It's a hint that we honor strongly.

[googlewebmastercentral.blogspot.com...]

[Globetrotter]

I have a question about the canonical, hopefully i may use this thread for it.

What if you have a website www.example.com and www.example.co.uk both of the urls show the same content. Should you use one canonical for both domains and point both them to www.example.com or should each domain have it's own canonical and show the cononical www.example.com of this domain and www.example.co.uk on the other?

[deadsea]

Google thinks of a canonical in a similar way to a redirect. If you say that one page is canonical of another and then point back with another canonical, it greatly confuses Googlebot. To the point where I've seen people saying that it shows up as a crawl error in webmaster tools.

You should choose one of your domains to be the "canonical" domain and point everything to the canonical domain. Google says that its OK to point a canonical tag on a page to that page itself.

[tedster]

I'd keep canonical links for the two domains separate, Globetrotter. Otherwise only the one you choose as the canonical will rank and that could hurt.

It's OK to have essentially duplicate content on a ccTLD, such as .co.uk. Localize the spelling and grammar for UK English and it's even better.

[alika]

In one of the sites I'm working on, we messed up the canonicals in March 2011. The web team uploaded a canonical pointing to a non existent URL.

The wrong canonicals were uploaded Thursday afternoon, and the Google traffic numbers compared to same day of the previous week shows that Google reacts fast:

Friday = 7% drop
Saturday = 23% drop
Sunday = 50% drop
Monday = 52% drop

We found the problem 11 days later, and by then Google traffic has dropped by 62%.

It's been several months, and our Google traffic is only about 90% of our March traffic. Recovery is slow, as our summer 2011 Google traffic was lower than summer 2010:

data compared to same month in 2010:
March 2011 = 41% lower
April 2011 = 43% lower
May 2011 = 16% lower

Recovery is not quick and immediate. From our experience, Google is not as forgiving and will not restore your traffic just because you fixed the problem. This is a PR 7 site that has not been affected by Panda.

Yes, be careful with canonicals. I have battlescars to prove it :o(

[aakk9999]

Google thinks of a canonical in a similar way to a redirect. If you say that one page is canonical of another and then point back with another canonical, it greatly confuses Googlebot. To the point where I've seen people saying that it shows up as a crawl error in webmaster tools.

Yes, this would show as "Redirect loop" in WMT.

Also if you put canonical from A to B and then have 301 from B to A, this also shows as "Redirect loop" in WMT