Canonical tag generator

A canonical tag exists because the same page is usually reachable at several URLs — with and without a trailing slash, with tracking parameters, over http and https, at www and without. Search engines see those as different pages with identical content and have to guess which to index. The canonical tag removes the guess.

Three rules decide whether it works. It must be absolute — a relative canonical is a common and silent failure. It must point at a URL that returns 200, because a canonical pointing at a redirect or a 404 is ignored entirely. And it must be self-referencing on the canonical page itself, which sounds redundant and is the standard advice: it costs nothing and settles the parameter variants automatically.

The most damaging mistake is a site-wide canonical pointing at the homepage. It is easy to do by putting the tag in a template with a hard-coded URL, and the result is that every page on the site tells Google it is a duplicate of the homepage — so the whole site drops out of the index except one page. If organic traffic collapses overnight after a template change, this is the first thing to check.

One clarification: a canonical is a hint, not a directive. Google can and does ignore one it disagrees with — if the content genuinely differs, or if the signals point elsewhere. It is a strong hint, but a noindex is the instruction.