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Canonical URLs & Duplicate Content

When to Use

When faceted pages create duplicate content issues — the same results appearing at multiple URLs with different facet parameter ordering.

Decision: Duplicate Content Sources

Source Example Problem
Parameter order ?f[0]=color:blue&f[1]=size:large vs ?f[0]=size:large&f[1]=color:blue Same results, different URLs
Empty facets ?f[0]=color:blue&f[1]= Trailing empty parameter
Default values ?f[0]=category:all "All" is the same as no filter
Pagination + facets ?page=2&f[0]=color:blue Each page × each facet combo
Pretty paths combos /search/color/blue/size/large vs /search/size/large/color/blue Path order variants

Pattern: Emitting rel="canonical" on Faceted Pages

Point every faceted variation at the base search page. Strip any canonical another module already set, then emit one for the unfiltered path:

/**
 * Implements hook_page_attachments_alter().
 */
function my_module_page_attachments_alter(array &$attachments) {
  $request = \Drupal::request();
  $facet_params = $request->query->all('f');

  if (!empty($facet_params)) {
    $base_url = $request->getSchemeAndHttpHost() . $request->getPathInfo();

    // Remove existing canonical.
    if (isset($attachments['#attached']['html_head_link'])) {
      foreach ($attachments['#attached']['html_head_link'] as $key => $link) {
        if (isset($link[0]['rel']) && $link[0]['rel'] === 'canonical') {
          unset($attachments['#attached']['html_head_link'][$key]);
        }
      }
    }

    $attachments['#attached']['html_head_link'][] = [
      ['rel' => 'canonical', 'href' => $base_url],
      TRUE,
    ];
  }
}

getPathInfo() drops the query string, so the canonical target is the unfiltered search page. Pair this with the meta noindex from SEO & Bot Protection — canonical consolidates signals, noindex keeps the combinations out of the index.

Pattern: Consistent Parameter Ordering

The QueryString URL processor generates parameters in a consistent order (by facet weight), which helps. But external links or bookmarks may use different orders.

Pattern: Hreflang with Facets

For multilingual sites, faceted URLs need hreflang tags. The facets module includes a LanguageSwitcherLinksAlterer that maintains facet parameters in language switcher links.

Pattern: Sitemap Exclusion

Do NOT include faceted URLs in your XML sitemap. Configure your sitemap module (simple_sitemap, xmlsitemap) to exclude:

  • Search pages with query parameters
  • Any path matching facet URL patterns

Common Mistakes

  • Including faceted URLs in sitemap — This explicitly tells bots to crawl all those combinations. Never include faceted URLs in sitemaps.
  • Appending a canonical without removing the existing one — Unset any rel => canonical already in html_head_link first, or the page ships two conflicting canonicals.
  • Forgetting pagination combinations — ?page=1&f[0]=color:blue and ?page=2&f[0]=color:blue are separate URLs. Canonical should typically point to page 1 or the unfiltered page.
  • Not handling rel=prev/next — If faceted pages are paginated, you need both canonical handling and proper pagination signals.

See Also