When I need to use canonical tag?

When I need to use canonical tag?

you should use the canonical tag every page for search engine

The canonical tag is used to mention duplicate content on our website. You can do it by specifying the “canonical URL” and enter “preferred” version of a web page. If you have duplicate content on your website then using canonical tag will help in SEO of your website.

A canonical link element is an HTML element that helps webmasters prevent duplicate content issues by specifying the "canonical" or "preferred" version of a web page as part of search engine optimization.
When to use Canonical:

-> When 301s can’t be implemented, or take too much time.
-> Duplicate content but you want to keep both pages live.
-> Dynamic pages with multiple URLs of a single page (from sorting features, tracking options, etc.).
-> Site-wide considerations like (domain/page/index.html vs. domain/page/ for the same page) can be easier with canonicals.
-> Cross-domain considerations where both sites are similar, but need to remain live.

A canonical tag is a way of telling search engines that a specific URL represents the master copy of a page. Using the canonical tag prevents problems caused by identical or "duplicate" content appearing on multiple URLs. Practically speaking, the canonical tag tells search engines which version of a URL you want to appear in search results.

The canonical tag is utilized to specify copy content on our site. You can do it by determining the "authoritative URL" and enter "favored" rendition of a site page. On the off chance that you have copy content on your site at that point utilizing standard tag will help in SEO of your site.

Canonical tags are used to tell spiders/crawlers which webpage must be returned from particular set of URLs. They should be used for avoiding 404 errors.