{"id":8879,"date":"2026-11-05T13:43:11","date_gmt":"2026-11-05T06:43:11","guid":{"rendered":"https:\/\/adtek.agency\/glossary\/canonical-tag\/"},"modified":"2026-11-05T13:45:58","modified_gmt":"2026-11-05T06:45:58","slug":"canonical-tag","status":"publish","type":"mona_glossary","link":"https:\/\/adtek.agency\/en\/glossary\/canonical-tag\/","title":{"rendered":"Canonical tag"},"content":{"rendered":"<p>A canonical tag is a <code>&lt;link rel=\"canonical\"&gt;<\/code> element in a page&#8217;s &lt;head&gt; that tells Google which URL is the main version when the same content is reachable at several URLs. Google treats it as a strong signal, but it is a hint, not a directive Google must follow.<\/p>\n<h2>What is a canonical tag, and where does duplicate content come from?<\/h2>\n<p>Google calls the process of picking one representative URL for a piece of content canonicalization. The chosen URL is the canonical URL: Google crawls it most regularly and shows it in search results (<a href=\"https:\/\/developers.google.com\/search\/docs\/crawling-indexing\/canonicalization\" target=\"_blank\" rel=\"nofollow noopener\">Google Search Central, What is URL canonicalization, accessed November 2026<\/a>).<\/p>\n<p>Duplicates usually appear on their own: HTTP and HTTPS versions, filter parameters such as <code>?sort=price-asc<\/code>, a mobile version on a separate URL, a staging site open to crawlers. Google says some duplication is normal and not a spam violation, but Google may show a URL you did not want.<\/p>\n<h2>How to declare a canonical URL<\/h2>\n<p>Google only accepts the element inside &lt;head&gt; and recommends absolute URLs:<\/p>\n<pre><code>&lt;link rel=\"canonical\" href=\"https:\/\/example.com\/ao-thun-trang\/\"&gt;<\/code><\/pre>\n<p>The main page should also point to itself, called a self-referencing canonical. For a PDF, send the canonical in an HTTP <code>Link<\/code> header.<\/p>\n<p>Google weighs the canonical tag with other signals: redirects are a strong signal, listing a URL in your <a href=\"https:\/\/adtek.agency\/en\/glossary\/xml-sitemap\/\">XML sitemap<\/a> is a weak one, and Google generally prefers HTTPS (<a href=\"https:\/\/developers.google.com\/search\/docs\/crawling-indexing\/consolidate-duplicate-urls\" target=\"_blank\" rel=\"nofollow noopener\">Google Search Central, How to specify a canonical URL, accessed November 2026<\/a>).<\/p>\n<p>Hypothetical example: 200 products, each reachable at 3 URLs (the product path, a path through a category, and one with <code>?color=<\/code>), for 600 URLs in total. Pointing the canonical to the product path tells Google there are only 200 main URLs.<\/p>\n<h2>Common canonical tag mistakes<\/h2>\n<p>Google lists these in its post 5 common mistakes with rel=canonical (<a href=\"https:\/\/developers.google.com\/search\/blog\/2013\/04\/5-common-mistakes-with-relcanonical\" target=\"_blank\" rel=\"nofollow noopener\">Google Search Central Blog, 2013, accessed November 2026<\/a>):<\/p>\n<ul>\n<li>The tag sits in &lt;body&gt;: Google ignores it.<\/li>\n<li>Missing https:\/\/, as in <code>example.com\/page\/<\/code>: Google reads it as a relative path.<\/li>\n<li>Two canonical tags pointing to different URLs, often because the theme and an SEO plugin both print one.<\/li>\n<li>Pages 2 and 3 of a category point to page 1, so products on later pages may not get indexed.<\/li>\n<\/ul>\n<p>The next three follow from Google&#8217;s general guidance, because they send conflicting signals:<\/p>\n<ul>\n<li>A canonical pointing to a redirected URL, a 404 or a <a href=\"\/en\/glossary\/noindex\/\">noindex<\/a> page; or a sitemap listing one URL while the canonical names another.<\/li>\n<li>Every page pointing its canonical to the home page because of a theme misconfiguration.<\/li>\n<li>Mixing http and https, or www and non-www, across canonicals, internal links and redirects.<\/li>\n<\/ul>\n<h2>Canonical tags and AI search<\/h2>\n<p>To appear as a supporting link in AI Overviews and AI Mode, a page must be indexed and eligible to show with a snippet; Google says there are no other technical requirements (<a href=\"https:\/\/developers.google.com\/search\/docs\/appearance\/ai-features\" target=\"_blank\" rel=\"nofollow noopener\">Google Search Central, AI features and your website, accessed November 2026<\/a>). Google shows only the canonical URL from a duplicate cluster, so a wrong canonical can make <a href=\"https:\/\/adtek.agency\/en\/glossary\/ai-overviews\/\">AI Overviews<\/a> link to a parameter URL instead of the page you want.<\/p>\n<h2>How to fix a missing canonical tag<\/h2>\n<p>Adtek&#8217;s <a href=\"https:\/\/adtek.agency\/en\/tools\/ai-search-checker\/\">AI Search Checker<\/a> looks for a canonical tag in the HTML (2 points). It does not check whether the URL is right, so review the mistakes above.<\/p>\n<ol>\n<li><strong>Yoast SEO:<\/strong> the plugin adds canonicals for you. To change one, open the post, go to the Advanced tab, enter the full URL in the Canonical URL field and update (<a href=\"https:\/\/yoast.com\/help\/canonical-urls-in-yoast-seo\/\" target=\"_blank\" rel=\"nofollow noopener\">Yoast, Canonical URLs in Yoast SEO, accessed November 2026<\/a>).<\/li>\n<li><strong>Rank Math:<\/strong> by default it uses the post&#8217;s current URL as the canonical. To change it, open the Advanced tab in the Rank Math meta box and fill in Canonical URL (<a href=\"https:\/\/rankmath.com\/kb\/advanced-tab\/\" target=\"_blank\" rel=\"nofollow noopener\">Rank Math, Advanced Tab, accessed November 2026<\/a>).<\/li>\n<li><strong>Shopify:<\/strong> Theme Store themes must include a canonical URL in their SEO metadata snippet (<a href=\"https:\/\/shopify.dev\/docs\/storefronts\/themes\/store\/requirements\" target=\"_blank\" rel=\"nofollow noopener\">Shopify, Theme Store requirements, accessed November 2026<\/a>). The Dawn theme ships <code>&lt;link rel=\"canonical\" href=\"{{ canonical_url }}\"&gt;<\/code> in layout\/theme.liquid (<a href=\"https:\/\/github.com\/Shopify\/dawn\/blob\/main\/layout\/theme.liquid\" target=\"_blank\" rel=\"nofollow noopener\">Shopify Dawn, GitHub, accessed November 2026<\/a>). If it is missing, add it via Online Store, Edit code.<\/li>\n<li><strong>Haravan, Sapo<\/strong> (Vietnamese e-commerce platforms): we found no official documentation on canonicals. View the page source; if the tag is missing, ask their support team.<\/li>\n<li><strong>Custom code:<\/strong> print the canonical in the &lt;head&gt; of every page from the server, with an absolute URL and no utm parameters. Google advises against changing the canonical with JavaScript.<\/li>\n<\/ol>\n<p>To check: press Ctrl+U to view the source, search for &#8220;canonical&#8221; and make sure there is exactly one tag. In <a href=\"https:\/\/adtek.agency\/en\/glossary\/google-search-console\/\">Google Search Console<\/a>, URL Inspection shows the User-declared canonical and the Google-selected canonical (<a href=\"https:\/\/support.google.com\/webmasters\/answer\/9012289\" target=\"_blank\" rel=\"nofollow noopener\">Search Console Help, URL Inspection tool, accessed November 2026<\/a>). If they differ, Google has not followed your hint. Then run the AI Search Checker again.<\/p>\n<h2>Frequently asked questions<\/h2>\n<h3>How is a canonical tag different from a 301 redirect?<\/h3>\n<p>A redirect sends both users and crawlers to the new URL. A canonical keeps every URL available to users and only hints to Google which one is the main version. Retiring the old URL? Use a redirect.<\/p>\n<h3>Can I block duplicate URLs in robots.txt instead?<\/h3>\n<p>Google advises against it. URLs disallowed in robots.txt can still be indexed without their content, and Google cannot crawl them to read the canonical.<\/p>\n<p>If you need a review of canonicals and indexing across your site, see Adtek&#8217;s <a href=\"https:\/\/adtek.agency\/en\/solution\/seo\/\">SEO solution<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A canonical tag is a &lt;link rel=&#8221;canonical&#8221;&gt; element in a page&#8217;s &lt;head&gt; that tells Google which URL is the main version when the same content is reachable at several URLs. Google treats it as a strong signal, but it is a hint, not a directive Google must follow. What is a canonical tag, and where [&hellip;]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"_yoast_wpseo_title":"Canonical Tag: What It Is, Common Mistakes and Fixes","_yoast_wpseo_metadesc":"What is a canonical tag? 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