Canonical tag

A canonical tag is a line in a page's code telling Google which version of a page is the real one when several URLs show the same content.

Online shops create this all the time, with the same product sitting at 5 URLs because of filters, sort orders and tracking parameters.

With the tag in place you tell Google which version you'd like to rank, and without it Google picks one itself.

Google treats it as a strong hint rather than an instruction, so it can choose a different page.

The reliable version is to have 1 URL per piece of content in the first place and use the tag to mop up what the platform generates.

A canonical pointing at a page that redirects, or at a page blocked from indexing, sends a mixed signal that Google may set aside.

What this means for you

This is plumbing, and done right it keeps the strength of 1 good page in 1 place instead of spread across 5 copies.

This one sits under SEO.

I'll look at what you've got and tell you where it stands, in the same plain terms.