Missing Canonical URL — Prevent Duplicate Content Issues

What is a canonical URL?

The <link rel="canonical"> tag tells search engines which version of a page is the "primary" or "original" version. When the same content is accessible through multiple URLs, the canonical tag prevents duplicate content issues.

Why does it matter?

Duplicate content problems

Without a canonical URL, search engines may see these as separate pages:

https://example.com/page
https://example.com/page?ref=newsletter
https://example.com/page?utm_source=twitter
https://www.example.com/page
http://example.com/page

This dilutes your SEO signals — instead of one strong page, you have five weak ones competing with each other.

How search engines handle duplicates

Google may choose the wrong URL as canonical
Link equity (backlinks) gets split across duplicate URLs
Crawl budget is wasted on duplicate pages
Rankings can drop due to content fragmentation

How to fix it

Add the canonical tag inside your <head>:

<link rel="canonical" href="https://yoursite.com/your-page" />

Best practices

Always use absolute URLs — https://yoursite.com/page, not /page
Use HTTPS — The canonical should be the HTTPS version
Be consistent with trailing slashes — Pick one format and stick with it
Self-referencing canonicals — Every page should have a canonical pointing to itself
Match with og:url — Your og:url and canonical should typically be the same URL
Include on paginated pages — Each page of a series should have its own canonical

Common mistakes

<!-- Bad: Relative URL -->
<link rel="canonical" href="/my-page" />

<!-- Bad: HTTP instead of HTTPS -->
<link rel="canonical" href="http://example.com/page" />

<!-- Bad: Includes query params -->
<link rel="canonical" href="https://example.com/page?sort=date" />

<!-- Good -->
<link rel="canonical" href="https://example.com/page" />

Relationship with og:url

Both canonical and og:url serve similar deduplication purposes, but for different audiences:

canonical → for search engines (Google, Bing)
og:url → for social platforms (Facebook, LinkedIn)

Ideally, both should point to the same URL.