Canonical Tags

01 The Rule

Every indexable page must include a self-referencing canonical tag. Duplicate or equivalent pages must canonical to the preferred version. Canonical URLs must be absolute and match the protocol, domain, and trailing slash convention of the canonical form.

02 Rationale

Without explicit canonical signals, search engines must infer which version of a page to index. For e-commerce sites where products appear under multiple categories, or sites with session/tracking parameters, this inference often fails — resulting in the wrong version being indexed or link equity being split.

03 Implementation

• Add <link rel="canonical" href="..."> to every indexable page
• Always use absolute URLs with protocol and domain
• Self-reference on pages without duplicates
• Point parameter/filtered variants to the clean URL
• Use HTTP Link header for non-HTML resources (PDFs, images)
• Ensure canonical URL returns 200, not a redirect

04 Common Violations & Consequences

05 The Fix

Implement canonical tags as part of your page template. Use a crawl tool to verify every page has a canonical that returns 200 and matches the sitemap URL. The Canonical Audit Tool automates this check.