Canonical Tag

A canonical tag is an instruction in a page's HTML that tells search engines which URL is the original when several addresses show the same or nearly the same content. It sits in the page head and looks like this:

<link rel="canonical" href="https://www.example.com/page/" />

Why one page ends up on several URLs

A webshop can serve the same category with and without filters in the URL, tracking parameters create new addresses for identical content, and many sites answer both with and without www or a trailing slash. With no original nominated, Google has to decide for itself which version belongs in the index, and the signals spread across several URLs instead of gathering on one.

How the signal works

The convention is simple: every variant points at the original, and the original points at itself. That last part is called a self-referencing canonical and is standard on well-run sites. The canonical signal consolidates backlinks and rankings on the nominated URL, and it keeps duplicate content out of the index.

A canonical tag is a strong hint, not an order. Google makes the final call on which URL it treats as canonical, and Search Console reports whether that choice matches the one declared on the page. Set up properly, canonicals also spare crawlers wasted work, which makes the tag one of the most used instruments in technical SEO. The guide to site health, redirects and canonicalization covers how canonicals are handled in practice.