When Should You Use Canonical Tags On your site?

1. Duplicate or Very similar Content

When you have content on multiple URLs that are very similar or duplicate of each other, then, these multiple URLs need to have canonical tags.

2. URLs That Serve the Same Search Purposes

Some URLs might not necessarily be duplicated, but do have the same search purpose; if such happens, I'll advise you to “canonicalize” it.

Let us look at these examples for better understanding; if www.example.com/a is about mobile phone and www.example.com/b is about mobile phone parts, their contents might be unique but they both have the same search purposes.

Your focus here should be on the URL's search purpose. It would be better to “canonicalize” these URLs even if they have different purposes but have similarities in their keywords.

3. When Updating or Republishing Old Content

These instances require the use of canonical tags. But if you, however, have the preference to keep your old URL, so as to get its ranking signal anytime you republish it, here is what to do: republish the content of the older URL as www.example.com/a-old.

You can then redirect and publish newer content at www.example.com/a and canonicalize it. Doing this will keep the older content on your website and will be treated as www.example.com/a-old.