What it normalises, and why each matters
| Step | Why |
| --- | --- |
| Force https | http and https are different URLs to a crawler |
| Drop www | so is www and the bare domain |
| Strip tracking | ?utm_source=… creates a new URL for every campaign |
| Trailing slash | /page and /page/ are two URLs on most servers |
| Drop index.html | /dir/ and /dir/index.html are the same page |
| Drop the fragment | never sent to the server, never part of a canonical |
Each of these silently splits ranking signals between URLs that show the same page. Canonicalising consolidates them.
The failure that looks like success
A canonical pointing at a URL that redirects, 404s, or has its own canonical pointing elsewhere is ignored — and there is no error anywhere to tell you. The tag is present, the page looks configured, and nothing is being consolidated.
Check that the canonical URL returns 200 and canonicalises to itself. The meta tag analyzer reads the tag off a live page.
Not a substitute for a redirect
If the alternate URLs have no reason to exist, redirect them. A canonical keeps both alive and asks a crawler to prefer one, which is right when both need to work and wrong when one is simply a mistake.
Questions
Does a canonical tag force Google to use that URL?+
No. It is a strong hint, not a directive. Google can and does ignore a canonical it disagrees with — most often when the two pages are not actually duplicates, or when the canonical points somewhere that redirects, 404s or is itself canonicalised elsewhere.
Should a page canonicalise to itself?+
Yes, on every page. A self-referencing canonical is what makes the whole mechanism work: it tells a crawler which of the many URLs that serve this page — with tracking parameters, with and without a trailing slash — is the real one.
Why is lowercasing the path optional when the host is always lowercased?+
Because hostnames are case-insensitive by specification and paths are not. On most servers `/Page` and `/page` are different resources, so lowercasing a path can point the canonical at a 404. Turn it on only if you know your server folds case.
Canonical or redirect?+
Redirect when there is one correct URL and the others should not exist. Canonical when the alternatives must keep working — a printable version, a page reachable through several categories, a URL carrying campaign parameters.