Duplicate Content and Canonical Tags, Explained Simply

Where duplicates come from

• —`http` vs `https`, `www` vs non-www, trailing slash variations.
• —URL parameters such as `?utm_source=` or sort and filter options in shops.
• —Print versions, tag pages or the same product in several categories.
• —Copying manufacturer descriptions or another site's text.

Your tools, strongest first

1. 1.301 redirect when the duplicate URL should not exist at all.
2. 2.Canonical tag on each version pointing to the preferred URL.
3. 3.Consistent internal links and sitemap that use only the preferred URL.

Checking what Google chose

Inspect a URL in Search Console: it shows the user-declared canonical and the Google-selected canonical. If they differ, look for conflicting signals such as links or the sitemap pointing elsewhere. The indexing errors guide covers the related statuses.

Myths

• —There is no general "duplicate content penalty" for ordinary technical duplicates; the cost is diluted signals and the wrong URL showing.
• —Copying other sites' content at scale is a different matter and can fall under spam policies.
• —A canonical is a strong hint, not a command.

Sources and limits

This is a practical guide based on public documentation and day-to-day SEO work. It reports no original dataset, guarantees no ranking, and gives no fixed timeline.

Google: Consolidate duplicate URLs

Google: Spam policies