Canonical URL
A tag telling search engines which version of a page is the primary one when duplicate or similar content exists at multiple URLs.
The duplicate content problem
Many sites have the same content accessible at multiple URLs—with and without www, HTTP and HTTPS versions, trailing slash variations, or URL parameters for tracking. Search engines struggle to determine which version to rank, potentially diluting your visibility across multiple copies.
Canonical tags solve this by explicitly declaring the "master" version. The tag <link rel="canonical" href="https://example.com/page"> tells search engines "this URL is the authoritative version; consolidate all ranking signals here regardless of which URL people access."
Common canonical scenarios
E-commerce product pages often appear in multiple categories—the same product accessible at /category-a/product and /category-b/product. The canonical tag should point to one primary URL, preventing duplicate content issues.
Paginated content like blog archives create similar challenges. Rather than fighting for rankings across /blog, /blog/page/2, /blog/page/3, canonical tags can consolidate signals to the main blog page or use self-referencing canonicals on each page.
Print versions, mobile-specific URLs (less common now with responsive design), and sorted/filtered views all benefit from canonical implementation pointing to the standard version.
Implementing canonicals correctly
Every page should have a canonical tag—even if it points to itself. This eliminates ambiguity about which version is authoritative. Place the tag in the <head> section alongside other meta tags.
Canonical URLs should be absolute, not relative—https://example.com/page instead of /page. Ensure they point to the HTTPS version if your site uses SSL. Incorrect canonicals can deindex important pages, so verify implementation carefully.
Canonicals and SEO
Proper canonical implementation consolidates link equity from all URL variations to your chosen version. External links to duplicate URLs pass their authority to the canonical version instead of fragmenting across multiple pages.
We configure canonical tags automatically in every Astro build, ensuring clean indexing and consolidated ranking signals from launch day.
Related terms
Why it matters
Understanding “Canonical URL” helps you speak the same language as our design and development team. If you need help applying it to your project, book a Fernside call.