How to use canonical tags to take care of duplicate content: Case Study of an E-Commerce site

Imagine how frustrating it will be if a SERP contains 10 URLs from the same website with the same content. It will be extremely tough to find quality content from different websites. This would probably be one of the best black hat SEO techniques (if it works out). Luckily enough for us, Google penalizes duplicate content and there is a tag which, if used, will help you in saving your website from getting penalized. It is the rel canonical tag.

According to Google, The rel=”canonical” link consolidates indexing properties from the duplicates, like their inbound links, as well as specifies which URL you’d like displayed in search results.

The rel=canonical tag tells the search engines about which URL does the site wants to list on the SERPs. If not used, it’ll create a clutter of useless pages (which are the same pages) and the SEO juice will be divided unnecessarily between those pages.

There are different URLs that a particular page might have. You need to check them and add the canonical tag.

“http://example.com/quality-wrenches.htm (Main URL)

http://www.example.com/quality-wrenches.htm(oops! all pages also resolve with the www sub-domain)

http://http://example.com/quality-wrenches.htm?ref=crazy-…(this looks like a way to track referral sources)

http://example.com/quality-wrenches.htm?sort=price(how users view the products by lowest to highest price)

http://example.com/quality-wrenches.htm/print

These are all URLs of the same page but they come out as different pages if the canonical tag is not used. The www and non www issue can be resolved using 301 redirects but you will have to use the canonical tag for the rest of them.

Flipkart’s case with canonical tags:

With e-commerce sites, the problem is having the same product in different color, size, memory(in case of laptops, phones etc. ). I will take the case of a product with different colors.

Nokia Lumia 520 comes in 5 different colors – Red, Yellow, White, Black and Cyan.

When I searched “nokia lumia 520 flipkart” on Google, this is how the result page looked:

The URL of the first result is http://www.flipkart.com/nokia-lumia-520/p/itmeyfpbsg7tajzj and it takes me to the Nokia Lumia 520(Red)’s page.

Next, I searched for Nokia Lumia 520 on their site which listed all the 5 colors. Following were the URLs of the pages:

Yellow: http://www.flipkart.com/nokia-lumia-520/p/itmeyfpbsg7tajzj?pid=MOBDJ4ZNPKRUWTV9

White: http://www.flipkart.com/nokia-lumia-520/p/itmeyfpbsg7tajzj?pid=MOBDJ4ZNC7PTMG68

Black: http://www.flipkart.com/nokia-lumia-520/p/itmeyfpbsg7tajzj?pid=MOBDJ4ZNAPHAUMSH

Cyan: http://www.flipkart.com/nokia-lumia-520/p/itmeyfpbsg7tajzj?pid=MOBDJ4ZNKFFGYJC4

Red: http://www.flipkart.com/nokia-lumia-520/p/itmeyfpbsg7tajzj?pid=MOBDJ4ZNY4G5TJEC

Note: I have removed the search parameters from the URLs for simplifying the URLs.

When I checked the source code for all these pages, the common code was

link rel="canonical" href="http://www.flipkart.com/nokia-lumia-520/p/itmeyfpbsg7tajzj"/

What this tells the search engines is that no matter what color people are searching for Nokia Lumia 520, show the page with Red Nokia Lumia 520! It may kill the user experience, but it’s better to have visitors coming to your site and finding the color they want instead of getting penalized and having no visitors at all.

To confirm the case, I searched “nokia lumia 520 white flipkart” on Google:

Voila! The URL is still of the Nokia Lumia 520 red’s page.

This confirms the fact that the Red Nokia Lumia 520’s page has been defined as the parent page of all other Lumia 520’s pages.

So now that you know how Flipkart uses the rel=canonical tag to list its pages, you should start implementing the same on your website. But before that, here are the errors to avoid when using the canonical tag:

1)The rel=canonical tag should only appear in the of the code. If declared more than once, Google might just ignore all the declarations.

2)Don’t send mixed signals. If you have 3 pages, say

a) http://example.com/quality-wrenches.htm

b)http://example.com/quality-wrenches.htm?ref=crazy-…

c) http://example.com/quality-wrenches.htm?sort=price

Now if page “a” has been canonicalized to page “b” and page “b” has been canonicalized to page “c”, it becomes complex for unnecessary reason. This is known as Daisy Chaining. Moreover, if you think something like this is going to happen, you should point the URLs to one single URL instead of creating a chain. Daisy chaining just confuses the crawlers.

You must also check if the page that you have canonicalized to – exists. In this case, hulk does not belong to team minions. Hence, it will give a 404 error. You will lose the value for all the pages.

These were few mistakes you should avoid while using the canonical tag. Feel free to share your thoughts in the comments section below.

Pro Tip: See what Matt Cutts has to say about how Google deals with Duplicate content.