Definition
A canonical tag is an HTML link element that tells search engines which URL is the preferred version of a page when similar or duplicate versions exist.
Canonical tag explained
The same content is often reachable at several URLs: with and without tracking parameters, through different category paths, in print versions, or with sort orders applied. A canonical tag in the head of each version, a link element with rel set to canonical, points to the one URL you want indexed.
Google describes rel canonical as a strong signal, not a directive. It lists several ways to indicate a canonical URL, including redirects, which it treats as the strongest signal, the rel canonical link element or HTTP header, and sitemap inclusion, which is the weakest. If signals conflict, Google may choose a different canonical from the one you specified.
Common mistakes include pointing every page's canonical at the homepage, canonicalizing to URLs that redirect or return errors, conflicting canonicals between the HTML and HTTP header, and using canonicals where a redirect or a noindex would be the right tool.
Example
Your product “Oak Dining Table” is reachable under /dining/oak-table, /sale/oak-table and with ?color=natural. Each version carries a canonical tag pointing to /dining/oak-table, so Google indexes that URL and credits it with the links and signals from all three.
Why it matters
Canonical tags consolidate ranking signals on one URL and prevent duplicates from competing with each other in search results.
Related service
Technical SEO
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Technical SEO servicesSources
- Google Search Central: How to specify a canonical URL (updated 10 Jul 2026)
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Related terms
- Duplicate contentDuplicate content is substantially the same content appearing at more than one URL, on the same site or across different sites.
- 301 redirectA 301 redirect is a permanent redirect: the server tells browsers and search engines that a URL has moved for good and sends them to the new address.
- Faceted navigationFaceted navigation lets shoppers filter a category by attributes such as size, color, brand or price, often creating a separate URL for each combination.
- IndexingIndexing is when a search engine processes a crawled page and stores it in its index, making it eligible to appear in search results.
- HreflangHreflang is an annotation that tells search engines which language or regional version of a page to show to users in different languages or countries.