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Canonical Link Element

Matt Cutts

Google Engineer

Thursday, Feb. 12, 2009

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Interesting Fact

Charles Darwin was born�200 year ago today:�February 12, 1809

How can we help

the web "evolve"?

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Duplicate Content

These URLs are all different:

www.example.com
example.com
www.example.com/
example.com/
www.example.com/index.html
example.com/index.html
www.example.com/Home.aspx
example.com/Home.aspx

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How to fix duplicate content issues?

Change your Content Management System (CMS) to generate only the urls you want. "Normalize" urls
Pick one "canonical" url and ensure you link consistently within your site
Make all the non-canonical urls do a permanent (301) HTTP redirect to the canonical/preferred url
Google's Webmaster Tools: specify www vs. non-www
Break ties in Google by submitting your preferred url in a sitemaps file

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Tough Duplicate Content Issues

Sometimes can't generate permanent/301 redirects
Can't help how people link to you
Uppercase/lowercase paths
Session IDs
Tracking codes, analytics, and landing pages
Sorting by ascending vs. descending
Breadcrumbs (the user's previous web page)

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Is this a common problem? Yes!

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New Option for Duplicate Content

Canonical Link Element at page level

On http://www.example.com/page.html?sid=asdf314159265

<head>

...

...

</head>

(Don't forget the final / at the end of the link tag.)

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High-order Bits

This is a hint, not a directive/mandate/requirement. Search engines choose when to use the suggestion
Far better to avoid dupes and normalize urls in the first place
If you're a power user, exhaust alternatives first
Be careful. Regular bloggers/websites may want to wait for their software to be updated
If we see abuse, we reserve the right to react as needed

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Questions and Answers

Q: Does this work across domains?

A: No, only on the same domain

Q: Does this work across subdomains/hosts?

A: Yes. So zeta.zappos.com could suggest www.zappos.com as a canonical url

Q: Can I use this to suggest http://example.com be the canonical url instead of https://example.com?

A: Yes, absolutely

Q: What's the difference between this and a 301/perm redirect?

A: They are very similar, but sometimes you don't have the easy ability to generate 301/permanent HTTP redirects

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Questions and Answers

Q: Do the pages have to be bit-for-bit identical?

A: No, but they should be similar. Slight differences are okay

Q: Can I use relative or absolute urls?

A: Yes, but we highly suggest that you use absolute urls. This is a powerful tool, and absolute urls leave less room for error

Q: Can you follow a chain of canonicals?

A: We may, but don't count on it. Point directly to the final url

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Questions and Answers

Q: What if I point to a 404? Or have an infinite loop? Or I point to an uncrawled url? Or www/non-www conflict?

A: Search engines will handle it as best we can. Don't cross the streams!

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Thanks

Joachim Kupke: Google engineer who did heavy lifting
Yahoo and Microsoft: for support of this link element too
Wikia: for trying this out on their wiki pages
Lots of webmasters for giving us feedback on this

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Resources

Blog post on Google webmaster blog:

http://googlewebmastercentral.blogspot.com/2009/02/specify-your-canonical.html

Yahoo blog post: http://ysearchblog.com/2009/02/12/fighting-duplication-adding-more-arrows-to-your-quiver/

Microsoft: http://blogs.msdn.com/webmaster/archive/2009/02/12/partnering-to-help-solve-duplicate-content-issues.aspx

Ask: http://blog.ask.com/2009/02/ask-is-going-canonical.html

Google Help Center documentation:

http://google.com/support/webmasters/bin/answer.py?answer=139394

Joost de Valk: WordPress, Magento, and Drupal

http://yoast.com/canonical-url-links/