Why it matters to a buyer
Most stores and content sites generate several URLs for the same content, through filters, tracking parameters or print versions, without meaning to, and each of those competes with the real page instead of supporting it. For a buyer, an incorrect or missing canonical is one of the more common reasons a page a team is proud of fails to rank: Google may have indexed a parameter version, a staging copy or a near-duplicate instead of the one the business wants shown.
How it is measured or applied
Every page declares a self-referencing canonical by default, and any near-duplicate, such as a filtered or sorted version of a category, points its canonical at the clean, primary URL. Google treats the tag as a strong hint rather than a command, and can choose a different canonical than the one declared if other signals, like internal links or the sitemap, disagree. It is checked in Search Console's page indexing report, which shows the canonical Google actually selected for a URL next to the one the site declared, exposing any mismatch.
Sources
- Consolidate duplicate URLs, Google Search Central
