Tooltrusty

Canonical Tag Checker

A canonical tag either consolidates your duplicate URLs or does nothing at all. This tells you which.

View the page source in your browser (Ctrl+U or ⌘+U) and paste the whole thing. Nothing is uploaded.

Needed to tell a self-referencing canonical from one pointing elsewhere.

0Canonical tags
—Self-referencing?
—Overall

Findings

    Suggested tag

    Runs in your browser. The HTML you paste is parsed in this tab with the browser's own DOMParser, which builds an inert document — scripts in your markup never run and nothing is requested from the pages it references. That means you can safely audit a staging site, a client page behind a login, or an unpublished draft.

    What the canonical Tag Checker does

    A canonical tag tells search engines which URL is the definitive version of a page. It exists because the same content is routinely reachable at several addresses — with and without www, with and without a trailing slash, over HTTP and HTTPS, with tracking parameters appended, through a print view, or as the same product listed under two categories. Left alone, search engines split the page's authority across those variants and pick a canonical themselves, sometimes the wrong one.

    The tag is easy to add and surprisingly easy to break. This checker looks for the specific ways it fails. Two canonical tags on one page cause Google to discard both, and duplicates are common when a CMS theme and an SEO plugin each insert one. A canonical containing UTM parameters points at a tracked variant rather than the clean URL, defeating the purpose. A canonical still pointing at http:// quietly undoes an HTTPS migration. A canonical placed in the body instead of the head is ignored entirely. And combining a canonical with a noindex robots tag sends contradictory instructions that Google resolves in ways nobody can predict.

    The important habit is self-referencing canonicals: every page should declare itself canonical unless it genuinely is a duplicate of another. It costs nothing, it stops parameter-laden variants being indexed, and it makes the intent explicit rather than leaving it to inference.

    How to use it

    1. Paste the page's HTML source into the box.
    2. Enter the URL the page was actually served from — the checker needs it to tell self-referencing from cross-referencing.
    3. Read the findings; red items break the tag, amber items are judgement calls.
    4. Use the suggested tag if the page should simply point at itself.

    A worked example

    A page reachable at four addresses:

    https://example.com/shoes
https://www.example.com/shoes
https://example.com/shoes/
https://example.com/shoes?utm_source=newsletter

    All four serve identical content. With a self-referencing canonical of https://example.com/shoes on every one of them, the four are consolidated into a single indexed page and any links pointing at any variant count towards it.

    Now the common failure. The newsletter variant is generated by a plugin that copies the full request URL into the canonical, producing <link rel="canonical" href="https://example.com/shoes?utm_source=newsletter">. That page now declares the tracked URL as the definitive one, and the tracked URL is what gets indexed — complete with the campaign parameter visible in search results. This checker flags it as an error.

    Frequently asked questions

    Should every page have a canonical tag?

    Yes, as a default. A self-referencing canonical on every page costs nothing and prevents parameter and case variants being treated as separate pages. Only point a canonical elsewhere when the page really is a duplicate of another.

    What is the difference between a canonical and a 301 redirect?

    A redirect sends users and crawlers to a different URL — the original stops being reachable. A canonical leaves both URLs working and tells search engines which to index. Use a redirect when the duplicate should not exist; a canonical when it needs to exist but should not be indexed separately.

    Can I canonicalise to a different domain?

    Yes, and it is the correct approach for syndicated content: the republishing site's canonical points at your original. Google treats cross-domain canonicals as a strong hint rather than an instruction, so it is not guaranteed to be honoured.

    Is a canonical tag an instruction or a hint?

    A hint. Google weighs it alongside internal links, sitemaps, redirects and which version it sees more often. Contradicting your own canonical — by linking internally to a different variant, say — makes it more likely to be overruled.