Canonical tag checker
A canonical tag tells search engines which URL is the main version of a page. Without one, the same page reachable at several addresses can be treated as duplicates. Paste your URL and Marlo checks whether your homepage has one.
Free. No signup. Open source.
What Marlo checks
- A <link rel="canonical"> in the page head
- That it holds a full https URL
- That there is only one
How to add a canonical tag
<link rel="canonical" href="https://example.com/">- Put the tag inside the <head> of the page.
- Use the full address you want shown in search results, with https and no tracking parameters.
- Add one per page, each pointing to that page's own preferred URL.
How common is it?
In Marlo's own audits of 365 homepages (as of 26 October 2026), "Missing canonical tag" was found on 137 sites, 55% of the 251 sites with two or more findings. That group is filtered and the sites came from a few directories, so treat it as a snapshot, not a base rate for the web. See the full numbers.
Questions
Does every page need a canonical tag?
It is good practice for every page you want indexed. A self-referencing canonical is fine and common.
What if the canonical points to a different page?
Search engines may treat the other page as the main one. Only do that when a page is truly a duplicate.
How do I use a canonical URL checker?
Paste your page address above. Marlo loads the page and reports whether a canonical link is present, whether it holds a full https URL, and whether there is more than one.
How can I validate or test a canonical tag by hand?
View the page source, search for rel="canonical", and confirm the href is the full address you want indexed. It should return a normal page, not a redirect or an error.
