What Is a Canonical URL and When to Use It

A canonical URL tells search engines which version of a page is the "master" copy. When you have similar or identical content across multiple URLs, the canonical tag helps consolidate ranking signals and prevents duplicate content issues.

What Does a Canonical Tag Look Like

The canonical tag goes in the <head> section of your HTML:

<link rel="canonical" href="https://example.com/product" />

This tells search engines: "This page is the primary version. Please index this URL instead of any duplicates."

Why Canonical URLs Matter for SEO

Prevents duplicate content penalties. Search engines may split ranking signals across duplicate pages, hurting all of them.
Consolidates link equity. Backlinks to duplicate pages pass their value to the canonical version.
Controls which URL appears in search. You choose the clean, preferred URL for users to see.
Saves crawl budget. Search engines spend less time crawling duplicate pages.

When to Use Canonical URLs

Product pages with parameters. example.com/product?color=red and example.com/product?color=blue should both canonicalize to example.com/product.
HTTP vs HTTPS. If both versions exist, canonicalize HTTP to HTTPS.
WWW vs non-WWW. Pick one and canonicalize the other to it.
Mobile and desktop versions. If you have separate URLs, use canonicals appropriately.
Print-friendly versions. Canonicalize print pages to the main article.
Syndicated content. If your content appears elsewhere, use canonicals to indicate the original source.

When NOT to Use Canonical URLs

Different content. Each unique page should have its own canonical pointing to itself.
Paginated content. Use rel="prev" and rel="next" instead of canonicalizing all pages to page 1.
As a redirect replacement. Canonicals are hints, not directives. Use 301 redirects when you want to permanently move users.

Common Canonical Mistakes

Pointing all pages to the homepage. This tells search engines your whole site is duplicate of one page.
Chain canonicals. Page A points to B, B points to C. Search engines may not follow the chain.
Canonicalizing to a 404 page. Always check that your canonical URL returns a 200 status.
Mixed signals. Your canonical says one thing, your sitemap says another. Keep them consistent.

Canonical vs 301 Redirect

Both consolidate duplicate content, but they work differently:

301 redirect: Sends users and search engines to the new URL. The old URL stops existing.
Canonical: Keeps both pages live but tells search engines which one to index. Users can still access both.

Use redirects when you want to permanently move traffic. Use canonicals when both URLs need to stay accessible.