Canonical tag: definition
The canonical tag, inserted in a page's <head> via link rel="canonical", tells search engines which URL should be treated as the reference version when several addresses show identical or near-identical content.
Why this tag is essential for an online shop
An e-commerce shop naturally generates many URL variants for the same content: filters by size or colour, sorting by price, pagination, tracking parameters added by a campaign. Without a canonical tag, a search engine can index each of these variants separately, spreading relevance across several URLs instead of concentrating it on one.
The canonical tag solves this by explicitly designating the reference URL: every variant points to it, and that is the URL Google favours in its results, even though it keeps crawling the others.
A typical case is a category page displayed with a sort order applied, for example a URL ending in ?order=price-asc: this page should carry a canonical tag pointing to the category URL without the sort parameter, so Google doesn't treat the two as separate, competing pages.
Frequently asked questions
Can a misconfigured canonical tag make a page disappear from Google?
Does every page on a shop need a canonical tag?
Do PrestaShop and WooCommerce handle the canonical tag automatically?
Describe your need in one minute
A few targeted questions so I can reply with an estimate rather than another questionnaire.