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What is the best way to handle canonicalization for product comparison pages? For example:

  1. Page that compares item 1 against item 2
  2. Page that compares item 2 against item 3

In the above example, the content for item 2 is duplicate - albeit the pages may contain an extra column for presenting descriptive content against each comparison e.g. item 1 is 10 meters wider than item 2. Do search engines penalize for this kind content duplication or it only happens when two pages have the exact same content on them?

My concern is that if there are a 100 products, it creates 4,950 possibilities of pages (with unique URLs) that compare each product to another product.

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Automatically generated combination pages should not be presented to search engines.

  • There is going to be a lot of duplication
  • Having Googlebot crawl a large number of such pages can decrease the crawling of the rest of your site
  • There usually isn't any search volume for comparison terms

Comparison features can be great for users on your site, but they are not a good way of attracting users from search engines. Use robots.txt to disallow search engine bots from crawling all those pages to begin with. If you do so, you won't have to worry about canonical tags at all.

If you find there is search volume for some combination. Spend more time on it. Write a more in depth article. Include the automatically generated comparison table.

There are some exceptions to this advice. For some product types users do search for comparisons. If you can build a good user experience on each comparison page you can get away with a lot of duplication in the text on the page. You would have to do a good job of generating unique page titles and meta descriptions for each page so there isn't duplication there. You would also want to make sure that you link prominently to the most popular comparisons (for example from the home page). You'll probably find that 20% of your comparisons get 80% of the interest and that 50% of comparison pages aren't even used at all. Advanced strategies rely on link sculpting to the popular ones and disallowing crawling and indexing of the unpopular ones.

  • Thanks Stephen. Your answer makes sense but I'm wondering how websites such as snapsort.com manage to stay clear from the wrath of search engines. I checked the robots.txt and don't see any comparison pages disallowed. Any idea how they might be doing this? – Zishan Dec 23 '15 at 14:28
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    That site does have 350,000 comparison pages indexed as well as 250,000 detailed comparison pages. I wouldn't say their strategy is optimal. Getting tons of pages into Google's index isn't always appreciated. I should also add that I have a currency conversion site that has a page for each pair of currencies, so I'm certainly willing to create lots of pages programaticay myself. I've added more to my answer. – Stephen Ostermiller Dec 23 '15 at 14:55

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