rel=canonical tag

Alan's picture
| 4th March 2009

So, Google, Yahoo, Microsoft and, more recently, Ask have announced the new "canonical" link type or, more colloquially, the rel=canonical tag. Much has already been written about this tag and its purpose: to help prevent duplicate content issues. Probably the best summary is this Matt Cutts video

This tag is a welcome addition to the armoury in the fight against duplicate content issues. In addition to Matt's comments, I would make the following points:

Copyright Protection

Scrapers are forever copying content and publishing it on their own sites/splogs. Sometimes they are exceptionally lazy or stupid, even to the extent that they copy Adsense code onto their own sites. If they copy your rel=canonical tag onto their site, that would give a strong "hint" to the search engine that you were the original owner of the content:


Microsoft Platforms

Matt made reference to the Microsoft platform in his video, but I would emphasise the point. Microsoft's implementation of RFC 2396 is flawed. The path component of a URL is supposed to be case sensitive, but Microsoft makes it case insensitive. If there are n alphabetic characters in the path, then a Microsoft implementation gives 2n possible variations of that path, where there should be only one. For example, if n=1 and the path is "/a/". Microsoft would allow "/a/" and "/A/"; if n=2 and the path is "/ab/". Microsoft would allow "/ab/", "/aB", "/Ab" and "/AB/"; and so on. 2n variations gives vast potential for duplicate content and it is a big issue with sites built on the Microsoft platform. The rel=canonical tag makes it very easy to specify the correct, case-sensitive path on a Microsoft platform:


Static Web Content

Static web content is content that is stored in the format in which it is delivered. Typically, static content is served under a static URL (a URL that does not contain a question mark). However, it is possible to link to static content and append query parameters, even though these query parameters will have no impact on the content that is served. One example of when this might happen is when a referrer parameter is passed to a JavaScript function within the static content:

Affiliate Link

Thousands of links can be created to a single, static URL, each with a different referrer query parameter attached. For sites built on static content, trying to manage such links has been difficult in the past. Now, it's relatively easy. Each page of static content simply needs to contain a rel=canonical tag:


Conclusions: rel=canonical

For the reasons stated above, I would recommend the use of a rel=canonical tag in all static content. In fact, I would recommend its use in all content, static or dynamic - with appropriate care of course. It's a powerful tag and using it wrongly could have dire consequences. In the next post I'll look at some of the limitations of the rel=canonical tag and consider some alternatives.

You might also like

Predicting The Future with Google
On 22nd March I spoke at an event featuring speakers from Arkle Finance, Enquir3, and Google, all sharing their expert knowledge on the subject of client acquisition and online marketing. Here’s an overview of the valuable information Joe McEntee of Google had to offer.
Alan Perkins
On: 29th March 2018
Posted In:
Silverdisc Organic Search Result
Your website’s position in Google’s search results is very important. Ranking in Google is our top priority when it comes to search engine optimisation (SEO), and as SEO experts in Northampton, I think we do a pretty good job.
Jess Lee
On: 8th February 2018
Posted In:
SEO | Google | Search Engines
Silverdisc SEO search engine optimisation
SEO is a complex subject, especially considering Google likes to keep you on your toes and change things around from time to time with their various algorithm updates. This is where we come in - as...
Jess Lee
On: 19th January 2018
Posted In:

Why Choose SilverDisc

Track Record Of Success

As a digital marketing agency with a 25-year history, continuously getting it right for our clients is of paramount importance and we have some great references to back this up.


Being Google Premier Partners and Bing Select Partners gives you the assurance that we’re fully trained, that we have demonstrated exceptional account management across a range of client spends and industries, and that our track record will continue.

Thought Leaders

We see where digital marketing is heading and position our clients to meet it. For example, we are so far ahead of the SEO game that we helped Google to write their webmaster guidelines, so you can enjoy SEO success without fear of being penalised.

Ethical & Honest

We have your best interests at heart and we give it to you straight, even if that’s painful to you or us. For example, we won’t spend your money marketing a website when it’s plain to us that the money would be wasted. We look for a win-win-win …


We listen to your individual needs, identify targets and work relentlessly towards meeting them, concentrating on what’s effective.


We exist to unlock the value of technology for business, and we love what we do. We have 25 straight years in digital marketing.

Friendly, Open and Giving

These words are at the core of our values. We build strong partnerships and go out of our way to help solve problems for clients, suppliers and the wider world.

Let's Get Started

Please fill in the form below or give us a call on 01536 316100

Follow SilverDisc