Canonical Tag is an important HTML tag on a page. It tells search engines that the page where the link was was found is the original/primary page. This tag can prevent duplicate content issues on your site. If you don't set one for the page, Google will set the page it has currently rendered/crawled as the canonical tag for the page. Thus, if two pages of the site have similar content, Google may not rank the page you want it to rank.
SEO plugins available for the WordPress content management system generate a canonical tag for your website and insert it between the head HTML tag. Sites that are built from scratch must include the code that generates the canonical HTML tag.
CrawlCenter shows the canonical link of the current page when you enter the page's URL in the text box you find above and click the "Check" button. Make sure you enter a valid non redirecting link in the textbox.
To check canonical tags/links in a bulk, use the CrawlCenter's site crawler tool (Register an account). CrawlCenter not only shows the canonical link for the various pages but also shows checks whether the URL of the page is equal to the canonical link. All you have to do is enter the domain name in the projects page of Crawlcenter, the number of URLs you want CC to process and click the "Crawl" button. If the URLs are different, you will see "false" status in the 3rd column of "Canonical report" of CrawlCenter. If the links are the same, you will see the "true" status.