Canonical URL

An HTML tag that tells search engines which version of a page is the "master" copy when duplicate or near-duplicate content exists at multiple URLs.

A canonical URL is specified using the <link rel="canonical" href="..."> tag in a page’s <head>. It signals to search engines which URL should be treated as the authoritative version when the same or very similar content is accessible at multiple addresses.

Common Scenarios Requiring Canonicals

• HTTP vs HTTPS versions of a page
• Trailing slash vs non-trailing slash URLs
• URL parameters (e.g. /product?color=blue vs /product)
• Paginated series where the first page content overlaps with later pages
• Syndicated content published on multiple domains

Self-Referencing Canonicals

It is best practice for every indexable page to include a self-referencing canonical — a canonical tag pointing to its own URL. This prevents accidental canonicalisation from scrapers or syndication.

Canonical vs Noindex vs 301 Redirect

• Canonical — preserves the duplicate URL but consolidates ranking signals to the preferred version. Use when you want to keep both URLs accessible.
• Noindex — removes the page from the index entirely.
• 301 redirect — permanently redirects one URL to another. The strongest signal; use this when the duplicate URL should never be directly accessed.