What is a canonical tag?#
It sits in the page’s <head>:
<link rel="canonical" href="https://example.com/blue-shoes/">It’s a strong hint, not a directive. Google considers it along with redirects, internal links, sitemaps and HTTPS when choosing the canonical URL — and may pick a different one if signals conflict.
Why it matters#
Duplicate URLs are surprisingly common: tracking parameters (?utm_source=…), sorting filters, HTTP vs HTTPS, trailing slashes, printer versions, or the same product in two categories. Without consolidation, ranking signals like links get split, and Google may show the wrong version.
Best practices#
- Add a self-referencing canonical on every indexable page (WordPress core does this for posts and pages).
- Use absolute URLs, including https and the preferred hostname.
- Point canonicals to pages that return 200 — not to redirects, 404s or noindexed pages.
- Keep signals consistent: internal links and sitemaps should use the canonical URL too.
- Don’t canonicalise paginated pages (page 2, 3…) to page 1.
Canonical vs 301 redirect#
| Use a canonical when… | Use a 301 when… |
|---|---|
| Both URLs need to stay accessible to users (e.g. filtered views) | The old URL should no longer be used at all |
| Content is syndicated to another domain | You moved or merged a page |
How to check#
Use the URL Inspection tool in Search Console to compare the “User-declared canonical” with the “Google-selected canonical”. If they differ, look for conflicting signals. Related: 301 redirect, thin content, keyword cannibalization.