How to Specify a Canonical URL - Why Specify a Canonical URL?

When you have multiple URLs showing the same or very similar content, you can tell Google which URL is the “main” or canonical one by using several methods — from strongest to weakest signals:

1. Redirects (Strongest Signal) #

Use 301 redirects to permanently point duplicate URLs to your preferred canonical URL.
This tells Google to treat the redirected URL as canonical.
Best when you want to get rid of duplicate URLs entirely.

2. rel=”canonical” Link Annotation (Strong Signal) #

Add a <link rel=”canonical” href=”https://yourcanonicalurl.com/page” /> tag in the <head> of duplicate HTML pages.
This tells Google that the specified URL is the preferred canonical version.
Use absolute URLs (full URL with protocol and domain).
Example:

<head>

<title>Product Page</title>

</head>

For mobile versions on a separate URL, also add a rel=”alternate” link for the mobile variant:

Use this method for HTML pages.
You can also specify canonical URLs via HTTP headers for non-HTML files like PDFs.

3. Sitemap Inclusion (Weak Signal) #

List your preferred canonical URLs in your XML sitemap.
Helps Google understand which URLs you consider important.
Easier to maintain on large sites.
Google will still decide which pages are duplicates and canonical.

4. Other Notes & Best Practices #

Don’t mix canonical URLs across methods for the same page (e.g., don’t have one URL in sitemap and a different one in rel=canonical).
Avoid using robots.txt or URL removal tools to control canonicalization—they don’t work for this.
Don’t use noindex to solve duplicates—it removes pages from search entirely.
Link internally to your canonical URLs rather than duplicates to reinforce preference.
If your site has HTTPS and HTTP versions, prefer HTTPS as canonical by using redirects and canonical tags.
For multi-language sites, specify canonicals within the same language group.

Summary Table

Method	Strength	Use Case	Notes
Redirects (301)	Strongest	When removing duplicates	Fastest way to consolidate URLs
rel=”canonical” tag	Strong	Preferred method for HTML pages	Must be in <head>, use absolute URLs
rel=”canonical” header	Strong (for non-HTML files)	PDFs, Word docs, etc.	Server configuration needed
Sitemap URLs	Weak	Large sites	Helps but doesn’t enforce canonicals

Why Specify a Canonical URL? #

Decide which URL appears in search results.
Consolidate ranking signals (backlinks, social shares).
Simplify analytics and tracking.
Save crawl budget by avoiding duplicate crawling.