Each website has pages that can be requested with different URLs. This can cause duplicate content issues with search engines.
Several things can lead to duplicate pages with different URLs:
- The HTTP and HTTPS version of a page.
- The www and non-www version of a page.
- Index and default pages (index.htm, index.php, /)
- Pages with and without trailing slashes
- URL parameters that do not change the content
- URL with session ID
- (The same content can be found in two different categories)
- Alternative page versions (regular, mobile, print version, etc.)
Although there is no duplicate content penalty, search engines may choose the wrong version for search results. The canonical tag allows you to show search engines the preferred version of the page.
What is the canonical tag?
The canonical tag is an HTML element that allows webmasters to avoid duplicate content issues by specifying the “canonical” or “preferred” version of a web page.
Actually, the canonical tag is an attribute of the link tag:
In this example, the canonical tag tells search engines that 'http://www.example.com/page.htm' is the preferred URL for the page, even if the same page is available at several different URLs. The canonical tag can be added in the main section of a page.
When should the rel='canonical' attribute be used?
The canonical attribute should only be used as a last resort. You should try to avoid duplicate content in the first place. Before adding the attribute, try the following to avoid duplicate content issues:
- Use 301 redirects to redirect old pages to their new versions.
- Use the robots.txt file to hide unwanted directories from search engines.
- Use CSS to create print or mobile versions of your web pages.
If your website uses faceted navigation, session IDs, etc., you should use the canonical tag to show search engines the preferred URL of the page.
What to go wrong?
If you don't use the canonical tag correctly, your rankings could drop. Here are some common mistakes:
- The canonical tag leads to a non-existent page.
- You use the same canonical tag with the same URL on all pages of your website.
- You put the canonical attribute in the body part of a web page instead of the head.
- The canonical tag links to another website. This is fine when you distribute your content on other websites. However, you should not use canonical tags with external links if you want to get high rankings for your own web pages.
When copying pages on your website, be sure to change the canonical tag. When developing a new website, don't forget to remove the placeholder URLs from the canonical tag.
Use absolute URLs in the canonical tag (https://www.example.com/page.htm) instead of relative URLs (/page.htm). Also, do not use the noindex tag on pages with the canonical tag. That can lead to indexing problems.
Can Google ignore canonical tag?
The canonical tag is not a directive. This means that search engines can ignore it. In the past, Google has said that they view the canonical tag as a strong recommendation. If the linked pages do not match sufficiently, Google may ignore the tag.
