Website pages make use of query string variables in a URL to display dynamic content. These query string variables create duplicate content for search engines. A canonical tag helps you optimize your pages for search engines by telling the search engines that one page’s content is relative to another. The search engines then index one page and remove the duplicate content from causing rank issues for your site.
When to Use a Canonical?
Most new webmasters get confused over the use of the canonical. For instance, you know you need to keep duplicate content out of the index, but what page should the canonical point to? The canonical should always point to a relevant page with similar content.
One common error webmasters make is pointing the canonical to the wrong page. For instance, many sites have paginated content. Webmasters point all subsequent pages to page one. This is incorrect. Webmasters should have a page where all products are shown and point paginated content to the full page of products.
Another common issue is using relative URLs rather than absolute URLs. Relative URLs point to only a directory and page within a domain. An absolute URL includes the “http” protocol, the full domain name and the directory and page name. You must use an absolute URL in your canonical settings.
Most blogs have a category page, and these category pages have duplicate content as you increase your article count. The best way to deal with duplicate category pages is to use a canonical that points to the featured article with the same content. Some webmasters de-index category pages because they are also a duplicate of the main home page as well as article pages. You don’t need to de-index these pages if you use a canonical tag.
Finally, you only use the canonical tag in the main header of an HTML file. It’s a mistake to put the canonical tag in the body or anywhere else on the page. Making this mistake can cause search engines to ignore your canonical settings.
Proper Canonical Syntax
After you figure out your canonical page and the page it should point to, you add it to your HTML code. Some blogging software has plug-ins you can use to set the canonical more easily. WordPress, Joomla and Blogger have canonical capabilities that are automated for people unfamiliar with customizing blog pages.
An example canonical link is the following:
Again, this HTML tag goes in the head section at the top of your pages’ HTML code. If you have a dynamic site such as PHP, these settings are usually placed in the “header.php” code. You might need to ask your web developer where the head section is coded and stored in your website application.
You can also set a canonical to another website if you run more than one website. Remember, the canonical tag is a suggestion and not a directive, so in rare cases Google might ignore the canonical tag, but it’s still useful in overall SEO efforts to remove duplicate content.
Use this tag carefully, because an incorrect canonical can cause massive SEO issues if implemented incorrectly. However, used correctly, the canonical tag can greatly improve the optimization of your pages and reduce duplicate content indexed in the search engines.