A canonical tag is a piece of HTML code (rel=”canonical”) that tells search engines which version of a page should be treated as the authoritative, primary copy when multiple URLs contain duplicate or very similar content.
Duplicate content issues are common on e-commerce sites (where a product might be accessible through multiple URL paths), sites with URL parameters, or sites available in print-friendly or mobile-specific versions. Without a canonical tag, search engines may split ranking signals across multiple URLs instead of consolidating them onto one.
Properly implemented canonical tags help preserve link equity and prevent search engines from wasting crawl budget on duplicate pages, ultimately supporting stronger, more consolidated rankings for the intended URL.
Canonicalization issues are one of the first things we check in a Technical SEO audit, since they can silently undermine an otherwise strong site.