What is a Canonical URL?

A canonical URL (or canonical tag) is an HTML element that specifies the preferred version of a webpage when duplicate or very similar content exists at multiple URLs.

It looks like this in your page's HTML: <link rel="canonical" href="https://example.com/blog-post" />

This tells search engines: "If you find multiple versions of this content, treat this URL as the original and rank it instead of the duplicates."

Why canonical URLs matter

Duplicate content confuses search engines and dilutes your SEO effectiveness. Sometimes the same or very similar content appears at multiple URLs: example.com/blog-post, example.com/blog-post?utm_source=twitter, example.com/category/blog-post. These might show identical content but be treated as separate pages, splitting ranking signals like backlinks across multiple URLs.

The canonical tag tells Google: "These URLs show similar content, but this one is the master. Credit everything to this version." All SEO signals consolidate to the canonical URL, preventing ranking dilution.

Common situations include pagination and sorting (e-commerce and blog archives with ?page=2 or ?sort=recent), tracking parameters (UTM codes creating duplicates), protocol variants (http vs https, www vs non-www), print-friendly versions, and syndicated content published on multiple sites.

How to use canonical URLs correctly

Most modern CMS platforms add canonical tags automatically. WordPress, for example, adds a self-referencing canonical to every page by default. If you syndicate content to other sites, they should add a canonical tag pointing back to your original URL - this tells Google you're the source.

For pagination, each page should have a canonical pointing to itself. Don't make all pages in a series point to page 1 - that tells Google only page 1 matters. Avoid canonical chains (A→B→C); always point directly to the final destination.

Check your canonical tags by viewing page source and searching for "canonical." SEO tools like Screaming Frog can audit your entire site for canonical issues. If you have duplicate content without good reason, fix the root cause rather than just adding canonicals. Use 301 redirects when content permanently moves - canonicals are for when URLs legitimately need to exist separately but contain duplicate content. Monitor crawling and indexing in Google Search Console to ensure canonical tags are working correctly.