A canonical tag (rel="canonical") tells search engines which version of a URL you want to appear in search results when you have duplicate or very similar content accessible through multiple URLs.
Why Canonical Tags Matter
- Prevent Duplicate Content: Avoid Google penalizing you for having the same content on multiple URLs
- Consolidate Link Signals: Combine ranking signals from similar pages to one preferred URL
- Manage Syndicated Content: Properly credit original content when republishing
- Simplify Tracking: Focus metrics on one URL instead of splitting across duplicates
- Preserve PageRank: Ensure link equity flows to the right page
When to Use Canonical Tags
- URL Parameters: example.com/page?ref=123 → example.com/page
- Tracking URLs: example.com/page?utm_source=email → example.com/page
- HTTP vs HTTPS: http://example.com → https://example.com
- WWW vs non-WWW: www.example.com → example.com
- Duplicate Product Pages: Multiple color variations of same product
- Print/PDF Versions: Point to the original web version
- Paginated Content: View-all page as canonical for paginated series
Canonical Tag Best Practices
- Use Absolute URLs: Include the full URL with protocol (https://)
- Self-Referencing: Pages should canonicalize to themselves when they're the preferred version
- Consistency: Make sure canonical tags are consistent across your site
- One Per Page: Only use one canonical tag per page
- Accessible: The canonical URL should be crawlable and indexable
How to Implement
Add this to your HTML <head> section:
<link rel="canonical" href="https://example.com/your-page/" />Common Mistakes
- Using relative URLs instead of absolute URLs
- Multiple canonical tags on one page
- Canonical pointing to a 404 or redirect
- Canonical in the <body> instead of <head>
- Using canonical to consolidate completely different content