canonical URL
Also called: preferred url, canonical tag, rel=canonical
A canonical URL is the single web address you designate as the master copy of a set of duplicate or near-identical pages. Google consolidates ranking signals onto it and usually shows that version in search results, though it treats your choice as a hint, not a rule.
How Google picks the canonical
Google clusters pages it judges to be the same or very similar, then selects one URL from each cluster as the representative. It uses that canonical page to evaluate content and quality, and points search results at it unless a duplicate fits a specific searcher better (a mobile URL for a mobile user, say).
You steer the choice with signals, not commands. From strongest to weakest: a permanent redirect, a rel="canonical" annotation, and inclusion in your XML sitemap. Google layers on its own site-setup signals, like preferring HTTPS over HTTP and honoring hreflang clusters. Reporting from Google suggests roughly 40 signals feed the decision, so a single tag can be overridden.
The tag lives in the page <head> or an HTTP header:
<link rel="canonical" href="https://example.com/product" />Practical rules straight from Google: use absolute URLs, put a self-referential canonical on the canonical page itself, don’t mix methods (a redirect plus a conflicting tag confuses the picker), and never use robots.txt or the removal tool to canonicalize. The usual sources of duplicates are tracking parameters, faceted filters, session IDs, print versions, and HTTP/HTTPS or www/non-www splits. Each one quietly spawns a URL Google has to reconcile against the one you actually want ranked.
How it affects your traffic
When canonicalization is wrong, Google splits link and content signals across several near-identical URLs, so no single version ranks as well as it should, and the URL that surfaces may not be the one you optimized. Parameter URLs, filtered category pages, and HTTP/HTTPS duplicates quietly eat crawl budget and dilute authority. Pointing canonical tags, redirects, and internal links at one clean URL is core on-page cleanup, and it's part of what our On-Page SEO service audits and fixes.
Get On-Page SEO that moves the needle
We turn terms like this into ranked pages and qualified pipeline. Start with a free Initial SEO Strategy.