Canonical links and duplicate content
The same page is often reachable at several addresses. A canonical tag nominates the one that counts, so ranking signals consolidate instead of splitting.
What it is
A canonical link is a line in the head naming the preferred address for the current page. It is a strong hint to search engines rather than an absolute directive.
Duplicates arise more easily than people expect: with and without www, HTTP and HTTPS, with a trailing slash and without, and with tracking parameters appended by an advertising campaign or an email newsletter.
Why it matters
If four addresses serve one page, links to that page may be divided between them, and none ranks as well as the combined total would.
It also wastes crawl budget, which matters on larger sites, and can produce the wrong address in search results.
How to fix it
- Add a self-referencing canonical to every page pointing at its preferred absolute address.
- Pick one host and one protocol, then redirect the alternatives with 301 redirects.
- Use absolute addresses, including https and the domain, rather than relative paths.
- Make sure the canonical points at a page that actually returns a 200 response.
What good looks like
<link rel="canonical" href="https://example.com.au/emergency-plumbing">Common mistakes
- Pointing every page's canonical at the home page, which tells search engines the rest of the site is not worth indexing.
- Canonical tags that point at a redirect or a missing page.
- Mixing signals, such as a canonical that says one thing and a redirect that says another.
Check your own site. ppclift checks this automatically on every page it audits. Run a free audit and see every check on one page, with no account required.