What Is a Canonical URL, and Why Does It Matter?

One page can often be reached through several addresses. A canonical URL is a small line of code that says, "if you see this page at different addresses, this is the one that counts."

Why one page ends up with many addresses

Tracking tags added to links from emails or ads create variations of the same address. So do the www and non-www versions, and the http and https versions. To a person they're all the same page. To a search engine, they can look like separate pages with identical content, the situation described in what duplicate content is.

What the tag does

The canonical tag points to the preferred address. Search engines then treat the variations as one page and gather the ranking signals in one place instead of spreading them thin.

How it differs from a redirect

A 301 redirect actually sends visitors to the new address. A canonical tag is only a hint to search engines; the visitor stays where they are. Redirects are for pages that moved. Canonicals are for variations that need to stay reachable.

Do you have to manage this?

Not day to day. It's set up once during the build, with each page naming itself as the preferred version. It's one of those details that matters because it's done quietly and correctly from the start.