Search & metadata
What is a canonical URL?
A canonical URL is the address selected to represent a page among duplicate or very similar versions; a website can suggest its preferred address, while search engines make their own selection.
By Plainview WebReviewed
The meaning
One piece of content can be reachable through several addresses. A campaign link might add tracking parameters, or a publishing system might expose more than one route to the same article. Canonicalization is the process of choosing a representative version of that content.
A site can express its preference with a rel="canonical" link in the page's HTML head. Redirects, internal links, and sitemap URLs also contribute signals. Keeping those signals consistent makes the intended address clearer. Google can select a different canonical, so the site's declaration should be understood as a preference rather than a command.
An example
Example: a fictional guide with a campaign link
<link rel="canonical"
href="https://example.com/guides/book-care">A fictional publisher shares https://example.com/guides/book-care?utm_source=newsletter&utm_medium=email&utm_campaign=autumn_reading. The tracking labels do not change the guide's content. The page declares the clean guide address as its canonical.
The visitor can still use the campaign URL, and that URL can carry useful analytics information. The canonical declaration does not remove its parameters or move the browser. It identifies the preferred representative of the matching content.
When it matters
Canonical choices help organize duplicate versions around a consistent address. For a business owner, the practical question is whether different URLs offer the same content or genuinely different pages. Different services should not all point to the homepage simply because that address seems more important.
Review the actual pages as well as the addresses. Plainview's checker compares supplied URLs and prepares markup; it does not fetch both pages, prove that their content matches, or report Google's selected canonical. Those questions need separate inspection of the website and relevant search reporting.
A common confusion
Canonical markup does not redirect visitors
A canonical declaration leaves the requested page available. A 301 redirect forwards the request to another address. Use the distinction when planning a permanent move: a canonical declaration on its own does not send someone following an old bookmark to the replacement.