What is a canonical tag?

The canonical tag is the <link rel="canonical" href="…"> line in a page's <head>. When the same content can be reached at several addresses (filter parameters, www and non-www, tracking parameters), it tells search engines which URL you want indexed. The most common use is a self-referencing canonical: every page points to its own address.

#Why it matters

Without a canonical, Google picks one of the duplicates itself, and it may not be the URL you want. Signals such as links and clicks can be split across copies. A canonical is a hint, not a command: if the content, internal links and sitemap contradict it, Google may choose another URL.

#Where you see it in SEOAsist

Technical Audit reports three issues:

Missing canonicals and canonicals pointing elsewhere can be closed with Auto-fix, which adds a canonical pointing at the page itself. If a page points elsewhere on purpose, mark it Intentional: Accept issues as intentional and auto-fix them. On top of that, Monitors → Index status counts pages where Google picked a different canonical from the one you declared as Canonical mismatch.

#Example

<!-- on https://site.com/shoes?color=black -->
<link rel="canonical" href="https://site.com/shoes">

The filtered page points to the main category page.

#Common mistakes

• Pointing the canonical at a redirected, 404 or noindex page.
• Setting every page's canonical to the homepage.
• Using a relative URL or the wrong protocol (http); always write the full, final URL.
• Canonicalizing page 2 and later of a paginated list to page 1; each page should point to itself.