Joe Majewski

What Does the Canonical Meta Tag Do? | link rel=”canonical”, huh?

In recent years, the meta tag and link relationship library has exploded. It’s not uncommon to have over a dozen different meta tags on a given page. As a web designer, it’s important to keep yourself up-to-date with these changes or you can quickly fall behind in the SEO (Search Engine Optimization) race.

Googlebot can’t figure out everything for itself, so it appreciates it when you, as a web designer, point it in the right direction by giving it various information through the use of these meta tags and link relations.

One particular tag that I find to be important is the canonical tag, which is still relatively new. This tag allows you to define the URL to a page that Googlebot will take interest in when said page has many different “views” through the use of URL variables. This is difficult to put into words, but I’m sure that with an example you will fully understand.

Imagine a page titled rankings.php, which lists the top players in some online game. Perhaps, by default, 50 members are shown per page. Now imagine if their were 125 members in this “game”. Then, rankings.php would have 3 different pages to view, most likely referenced by a $_GET variable passed through the URL. Thus, here are all the different ways that this page can be accessed:

1. rankings.php?page=1 would list the first 50 members
2. rankings.php?page=2 would list members 51 through 100
3. rankings.php?page=3 would list members 101 through 125
4. rankings.php would assume that page=1, showing the same content as rankings.php?page=1

There is already a duplicate content issue, as simply viewing the default page shows the same content as you’d see if you added the URL variable ?page=1. Googlebot hates duplicate content.

Now imagine if you also had a sort feature, where you could sort users alphabetically by their username or by their ranking, both with ascending and descending options. I couldn’t even begin to list all of the possible combinations anymore, especially if there were more than just three pages of users, but I’ll do it anyways:

1. rankings.php?page=1?sort=username&order=ascending
2. rankings.php?page=2?sort=ranking&order=descending
3. rankings.php?sort=username
4. rankings.php?sort=username&order=ascending

Assuming that the default page ordering was ascending, then examples one, three and four are ALL duplicate content pages.

Naturally, Googlebot would crawl the site, following all paths of links that it can find, and you would quickly find that hundreds of pages are being indexed just for the rankings page, many of them showing duplicate content. Although not proven to be fact, many believe that this has a negative impact on your PageRank.

If you aren’t familiar with, or simply just don’t know a whole lot about how it works, I highly recommend reading an article that I wrote about Google PageRank.

Here’s where the canonical tag comes into play. By simply placing a single meta tag into your source code, you can tell Google to not bother with all of the hundreds of combinations of URL variables that can be created to dynamically generate the rankings list. It looks a little bit like this:

<link rel = “canonical” href = “http://example.com/rankings.php” />

By simply placing that tag in your source code, it will tell Googlebot to only take concern with that URL structure for rankings.php. This means that all of the ?page=x and ?order=asc won’t have any affect on your site’s indexing or PageRank.

This may not have been the greatest example to use, as many people would disallow Googlebot from indexing a rankings page at all, and even if they did want the rankings page to be indexed, they could add “no-follow” to the sort links. Although not foolproof, there are other ways around the issue in some cases.

Nonetheless, my intention was to inform you about the “canonical” tag, and not to provide you with the perfect example case for when to use it. If you have any questions about the use of this tag, ask away in the comment section below.

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