Canonical Tags Explained: Telling Google Which Page Is the Original

On this page

1. How duplicate URLs happen
2. How a canonical tag works
3. WordPress and canonicals
4. Common mistakes
5. Canonicals vs redirects vs noindex

The same page can often be reached through several URLs. A canonical tag tells search engines which URL is the main version to index and rank, so ranking signals aren't split across duplicates.

How duplicate URLs happen

• http vs https, and www vs non-www versions
• Tracking parameters (?utm_source=...)
• Sorting and filter parameters on stores and listings
• Print versions or session IDs
• The same product in multiple categories with different URLs
• Content syndicated on other sites

How a canonical tag works

A canonical is a link tag in a page's head pointing to the preferred URL. Each page usually points to itself (a self-referencing canonical), while duplicate versions point to the main one. Google treats canonicals as a strong hint, not a command.

WordPress and canonicals

WordPress and SEO plugins add self-referencing canonicals automatically. Check them after migrations, domain changes and redesigns. Every page on this website includes one.

Common mistakes

• Canonicals pointing to a staging or old domain after a migration
• All pages canonicalised to the homepage, which tells Google to ignore them
• Canonical to a redirected or 404 URL
• Conflicting signals: canonical says one URL, sitemap and internal links use another
• Using canonicals instead of redirects when a page has permanently moved

Canonicals vs redirects vs noindex

• Redirect: the old URL shouldn't exist any more (page moved). See 301 vs 302 redirects.
• Canonical: duplicates need to exist, but one version should rank
• Noindex: the page shouldn't appear in search at all

For more on duplicates, see duplicate content explained.