Security & SEO

    Canonical tag check

    Crawls your top pages and flags missing, self-referential loops, cross-domain, or conflicting canonical tags — the top-3 SEO indexation bug.

    Updated 2026-07-10
    1 min read
    canonical
    seo
    indexation

    Quick answer#

    On every SEO crawl we extract <link rel="canonical"> and Link: rel=canonical headers, then check for missing, mismatched, or cross-domain values.

    What it checks#

  1. Every crawled page has a canonical
  2. Canonical resolves to a 200 (not 3xx / 4xx)
  3. No cross-domain canonicals unless intentional
  4. HTTP header and HTML tag agree

    5. Where to find it in Lemwatch#

    Site details → SEO → Canonicals.

    How to fix#

  5. Add a self-referential canonical on every indexable page.
  6. On paginated pages, point canonical to page 1 only if content is duplicated.
  7. Kill conflicting canonicals in HTTP headers if you also set the HTML tag.
  8. Re-crawl.

    9. FAQ#

    Do canonicals block indexing?#

    No — they consolidate signals. Use noindex to block.

    Do CMSes get this right?#

    WordPress + Yoast: yes. Shopify: often needs manual overrides on collection pages.

    Related#

  9. Robots.txt check
  10. Hreflang tag check
  11. Structured data check
    12. Was this article helpful?

    Previous

    Certificate chain check

    Next

    Robots.txt check

    Related Articles

    Robots.txt check

    Fetches robots.txt hourly and alerts on syntax errors, disallowed indexable paths, or blocked search-engine bots.

    Hreflang tag check

    Validates hreflang tags across your language variants — return-tag mismatches are the #1 cause of Google demoting international sites.

    Structured data (JSON-LD) check

    Validates schema.org JSON-LD on every crawled page against Google's rich-results eligibility rules.

    Understanding Your Security Grade

    How LemWatch calculates your overall security grade.

    Back to Help Center