What Is a Canonical Tag, and When Do You Need One?
A canonical tag names the address you want treated as the real one for a page. The Canonical Tag Generator produces it, and the problem it solves is more common than people realise.
The problem
The same page is often reachable at several addresses without anyone intending it. With and without www. With and without a trailing slash. Over http and https. With a tracking parameter attached. With a session id. Sorted differently, filtered differently, paginated differently.
To a search engine those are separate URLs with identical content. The consequences are real: the ranking signals are split between the versions instead of accumulating on one, and the engine has to guess which to show. A canonical tag removes the guess.
It is a hint, not an instruction
This is the part that surprises people. Google treats the canonical as a strong suggestion rather than a directive, and it will override you if the evidence disagrees - if your internal links, your sitemap and your redirects all point somewhere else, or if the pages are not actually duplicates.
So the canonical has to be consistent with everything around it. Pointing it at one address while linking internally to another is a conflicting signal, and the engine resolves it however it sees fit.
Four ways to get it wrong
Pointing every page at the homepage. This happens with badly configured templates and it tells Google your entire site is one page. Devastating and surprisingly common.
A relative URL. Use the absolute address, including the protocol and domain. A relative canonical is interpreted against the current URL, which can produce something meaningless.
Canonical on a noindex page. The two instructions conflict - one says consolidate here, the other says do not list this. Pick one.
Chains. A canonical pointing at a page whose canonical points somewhere else. Point directly at the final destination.
Self-referencing is good practice
Every page carrying a canonical pointing at itself sounds pointless and is useful: it establishes the preferred form of the address, so a visit with a tracking parameter attached still consolidates on the clean version. The UTM Link Builder produces exactly the parameters this handles.
Where the duplicate is genuinely permanent, a 301 redirect is stronger than a canonical, because it removes the duplicate rather than labelling it. Use a canonical when both versions need to remain reachable.
Common questions
Does it work across domains?
Yes, which is how syndicated content should credit the original.
Can two pages canonical to each other?
No - that is a loop and will be ignored. One is the canonical; the other points at it.
Does it help with paginated lists?
Not by pointing every page at page one, which loses the deeper pages. Let each page be its own canonical.
Where does the tag go?
In the head of the document, alongside the other meta tags.
Need a canonical tag for a page?