Resolving and preventing duplicate content issues are key to improving your search rankings. Canonicalization is one of the solutions you can use immediately.
With a canonical tag, a webmaster is able to optimize a website easily in favor of presenting the preferred version of a piece of content - which inevitably allows for better indexing by search crawlers.
The definition of canonicalization is the process of using a canonical tag to specify the preferred URL for a web page to show visitors, where several copies or choices of the same web page exist. Through this process, search engines are able to determine that links to different versions of a single content should act as links supporting the selected canonical version, thus improving the content’s performance in the SERPs.
A canonical tag example looks something like this:
<link rel="canonical" href="http://example.com/page1/product">
A 301 redirect is only used for a web page that has been moved to a new URL permanently. This will transfer any link juice powering the old URL to the new URL and also tell search engines to index the newly redirected URL instead.
A canonical tag is used in scenarios where multiple pages of the same content exist on the internet and you want search engines to know that the other versions are meant to supplement the canonical version. This in turn gives credit to the original content - not the non-canonical pages.
Not specifying a canonical tag for identical content will lead search engines to decide on their own which piece of content to index on their own, which may or may not be the best version of your content there is.
There may be scenarios where you have similar content spread across your website which may penalize your rankings if not optimized properly. Canonical tags will serve to sort duplicate content issues out and point crawlers in the right direction for ranking purposes.
Here are some common scenarios where canonical tags are used for SEO:
When you have 10 users logged into your e-commerce site at one time, and 10 URLs of the same product page are generated due to individual session IDs, you want those tags in place to prevent duplicate content penalization.
For example: your domain is http://example.com and you have two subdomains https://www.example.com and http://www.example.com. You can use canonical tags within those subdomains to specify that http://example.com is the main domain for indexing, and that any link juice granted to these subdomains should support the main domain only.
To make sure your website does not get penalized due to duplicate content, you will need to use canonical tags to let search engines know that the content featured on both mobile and desktop are similar.
Using canonical tags in a scenario like that will help ‘explain’ to search crawlers that category URLs generated all point back to the same page, which will also help with directing any backlinks to the original content.
To start adding canonical tags to your web pages, you should:
Every optimization step taken goes a long way in your SEO. Use canonical tags and get those duplicate content issues sorted for better ranking in search results.