What a canonical does
When the same content is reachable at several URLs (with and without a trailing slash, with tracking parameters, over http and https), the canonical tells search engines which one to index. It's a strong hint, not an order: a canonical that contradicts redirects, sitemaps or internal links may be ignored.
What is checked
- Missing canonical, several canonicals, empty or invalid values.
- Relative URLs (use the full https:// address).
- Whether the canonical points to the page itself, and if not, why: another host, http instead of https, a trailing slash difference or other parameters.
Frequently asked questions
Should every page have a self-referencing canonical?
It's a good default. It protects against duplicate URLs created by parameters and scrapers.
Why does my page say canonical points to another URL?
Either it's intentional (a variant pointing to the main version) or a template sets the same canonical everywhere, often the home page. The second case keeps pages out of the index.