正典タグ
A Canonical Tag (rel="canonical") is an HTML element that helps webmasters prevent duplicate content issues by specifying the "master" or "preferred" version of a web page. It tells search engines to index this specific URL and ignore other identical or near-identical versions.
Preventing Duplicate Content Penalties
In multilingual SEO, you might have similar pages for regional variants (e.g., US English vs. UK English vs. Australian English). Without proper canonical + hreflang tagging, Google may penalize these as "duplicate content" since the text is mostly identical. Canonical tags tell Google which version is the "original," while hreflang handles the language swapping. All "link juice" (ranking authority) flows to the canonical URL, preventing authority dilution. This is especially critical for e-commerce sites where product URLs might have sorting parameters (?color=red, ?size=large) that create duplicate pages.
Without vs. With Canonical Tag
現実世界の影響
E-commerce site has product.com/item and product.com/item?utm=ad
Google sees duplicates, splits authority
Page ranks #8 instead of #3
Add <link rel="canonical" href="product.com/item" />
Google consolidates signals to main URL
Page jumps to #3, traffic increases 40%