What is a canonical URL
Duplicate content is often complex to manage in order to optimize a site’s performance and page ranking on search engines like Google. Fortunately, canonical URLs can solve some of these problems and improve the SEO performance of articles that span multiple pages. Here are some pointers on what a canonical URL is and how to properly use it.
Avoid duplicate content
There are many situations where a page can be available by multiple URLs, usually due to poor site design. This is a problem for SEO because to analyze a web page or any indexable web document, search engines work with the principle 1 page = 1 URL. If the URL is different, it is a priori another page, but Google analizes it differently. The canonical URL indicates where the page should be. All other versions, which until now caused duplicate content, will now be considered as strictly the same page by the engines.
Save time and clicks
The canonical URL will also avoid internal duplicate content on the same website. This concerns for example a product sheet, which can be repeated on several pages of the website. For the engines to index the most valuable page in terms of SEO, it is more prudent to canonicalize all pages in a given website.
The difference with 301 redirect
The ideal would be to canonicalize all the pages of your site. This solution has a lot of similarities with the 301 redirect which pushes the engine to choose one page rather than another. The difference is that the canonical URL is only for search engines and for indexing while the 301 redirect simply sends engines and users from an old page to a new one, which is more like an update.
When to use it?
The rule for using the canonical tag is simple: use it whenever pagination is possible or likely. In practice, this occurs in three cases: when a content is spread over several pages, when pages are generated dynamically and when the same content has different URLs.
How to do it
To place a canonical tag in the HTML header of your page, simply use this format:
<link rel=”canonical” href=”URL” />
When learning what a canonical URL is, remember: it is still a patch. It is really best to make sure that each content is always accessible at the same URL.