Canonical URLs

Introduction

A canonical URL (rel="canonical") is an HTML link tag that tells search engines which version of a URL you want to appear in search results. It solves duplicate content issues.

Why it matters

If your site can be accessed via multiple URLs (e.g., http://example.com, https://example.com, https://www.example.com, or with tracking parameters like ?utm_source=twitter), search engines might index them as separate pages. A canonical tag consolidates these into one master URL.

Where it appears

Invisible to users, located in the <head> of your HTML document.
Search Engine Indexes (Google, Bing).

Requirements

A valid, absolute URL inside a <link rel="canonical"> tag.

Best Practices

Always use absolute URLs (e.g., https://example.com/page), not relative paths (/page).
Self-referential canonical tags are good practice (a page pointing to itself).
Ensure the canonical URL returns a 200 OK status.

Common Mistakes

Pointing a canonical tag to a 404 page or a redirect.
Using relative URLs.
Having multiple canonical tags on the same page.

Implementation

<head>
  <!-- Other meta tags -->
  <link rel="canonical" href="https://www.example.com/learn/canonical" />
</head>