Technical SEO
Canonical Tags and Duplicate Content for Non-Developers
Where duplicates come from, how to choose a canonical URL and how to check which one Google picked.
By the Seozumi editorial team · · about 5 min read
“Duplicate content” sounds alarming, but on most small sites it is not a penalty issue. It usually means the same page is reachable at several URLs, and Google has to guess which one to show. Canonical tags and consistent linking help you tell Google which version you prefer.
Where duplicates come from
| Cause | Example URLs for the same page |
|---|---|
| http vs https | http://example.com/shoes/ and https://example.com/shoes/ |
| www vs non-www | https://www.example.com/ and https://example.com/ |
| Trailing slash | /shoes and /shoes/ |
| Parameters | /shoes/?sort=price and /shoes/?utm_source=newsletter |
| Product variants | /boot?color=brown and /boot?color=black with identical text |
| Print or AMP versions | /article/ and /article/print/ |
What a canonical tag does
A canonical tag is a line in the page’s <head> that names the preferred URL:
<link rel="canonical" href="https://www.example.com/shoes/" />It is a strong hint, not a command. Google considers it alongside redirects, internal links and sitemaps when choosing a canonical. Google explains this in its guide to consolidating duplicate URLs.
Choose one version and signal it everywhere
- Pick your preferred protocol and host (for example
https://www.) and 301-redirect all others to it. - Use one trailing-slash style consistently and redirect the other.
- Put a self-referencing canonical on every indexable page.
- On parameter or variant duplicates, point the canonical to the main URL.
- Link internally only to the canonical versions.
- List only canonical URLs in your sitemap.
When not to use a canonical
- Pages that are genuinely different (two different products, two different articles) should each be self-canonical.
- Translated pages: each language version should be self-canonical and connected with hreflang. See multilingual SEO.
- Pages you want removed entirely: use a redirect or noindex instead.
- Paginated series (page 2, 3…) should usually be self-canonical rather than all pointing to page 1.
Check which canonical Google chose
Use URL Inspection in Search Console. It shows the “User-declared canonical” and the “Google-selected canonical”. If they differ, look for conflicting signals: internal links to the other version, the sitemap listing a different URL, redirects, or near-identical content.
The Pages report also lists statuses such as “Duplicate, Google chose different canonical than user” and “Alternate page with proper canonical tag” (the latter is normal and fine).
Content duplicated across sites
If you syndicate articles to other sites or copy manufacturer descriptions, Google may show the other version. For syndication, ask partners to link back and, where possible, add a canonical pointing to your original. For product descriptions, write your own; see product page SEO.
Common mistakes
- Every page canonicalized to the homepage due to a template error.
- Canonical pointing to a URL that redirects or returns 404.
- Canonical tags using http while the site is https.
- Two canonical tags on one page, often from a theme plus a plugin.
