How to use canonical tags correctly

Why it matters

Duplicate URLs are everywhere: the same page with and without www, with tracking parameters, with a trailing slash, or in print and filtered views. Google picks 1 version to show, and it will not always pick the one you want.

Telling Google your preference consolidates links and metrics onto 1 URL, makes reporting cleaner, and keeps crawlers from spending time on copies. Google says none of this is required, since it will choose a version on its own, so the goal is control and tidy data.

Key takeaways

• Redirects and rel=canonical are strong signals. A sitemap is a weak one. Using several together is more effective.
• Put a self-referencing canonical on every page you want indexed, using an absolute URL.
• Do not use robots.txt, noindex, or the URL removal tool to choose a canonical.
• Keep every signal pointing to the same URL, including internal links and the sitemap.

Step by step

1. Find the duplicates

   List the ways 1 page can be reached: http and https, www and non-www, trailing slash, uppercase and lowercase paths, tracking and sort parameters, and printer-friendly versions. Crawl the site or use the Page indexing report in Search Console to see which duplicates exist.

2. Choose the preferred URL for each set

   Pick the clean, permanent address you want people to land on. Prefer the version with no parameters, on your main host and protocol. Write the choices in a sheet so developers and editors work from the same list.

3. Pick the right method

   Use a permanent redirect when you are retiring a duplicate and nobody needs it. Use rel=canonical when the duplicate must stay reachable, such as a filtered view. Use the HTTP header version for PDFs and other files. Choose either the link element or the header, not both.

4. Add self-referencing canonicals

   Put a link rel=canonical element in the head of every indexable page, pointing to its own absolute URL, and on duplicates pointing to the preferred page. Use full URLs, not relative paths. Google recommends the self-referencing tag on the canonical page itself.

5. Line up every other signal

   Link internally to the canonical URL only. List only canonical URLs in your sitemap. Do not point a sitemap at 1 URL and a canonical tag at another for the same page.

6. Handle JavaScript rendering carefully

   If a script builds your pages, set the canonical in the HTML source and make sure scripts do not change it. If you cannot set it in the source, leave it out of the source and set it only with script. Mixed versions confuse the signal.

7. Verify in Search Console

   Inspect a sample of URLs and compare the user-declared canonical with the Google-selected canonical. If they differ, look at whether the pages are actually similar, since Google will not treat a page as a duplicate if the content is different. Fix the mismatch or the signals.

8. Monitor over time

   Watch the Page indexing report for statuses such as duplicate pages and alternate pages with a proper canonical tag. Google says a duplicate flagged there is usually fine, since it means the canonical was found. Investigate only when an important page is the one left out.

Example markup

<head>
  <title>Water heaters in Hartford</title>
  <link rel="canonical" href="https://example.com/water-heaters" />
</head>

<link rel="canonical" href="https://example.com/water-heaters" />

Link: <https://example.com/guides/water-heater-guide>; rel="canonical"

Questions