A canonical URL is the single URL declared as the master address for a page's content — the one search and answer engines should attribute citations to when the same content is reachable at multiple addresses.
A canonical URL is the single URL declared as the master address for a page's content — the one search and answer engines should attribute citations to when the same content is reachable at multiple addresses.
Google's canonicalization documentation covers the mechanism: a <link rel="canonical"> in the HTML head plus consistent internal linking.
Canonical URLs matter for AI answers because they tell the retrieval layer which single URL should carry the citation credit when the same content is reachable at multiple addresses — without a canonical, the model may cite the wrong copy or split authority across duplicates.
Large sites should structure their sitemap as a sitemap index pointing at multiple child sitemaps, each holding up to 50,000 URLs or 50MB uncompressed, and reference the index from robots.txt so every crawler — search and AI — can discover the full URL surface in one round trip.
Markdown twins are plain-text or markdown copies of an HTML page served at a parallel URL (typically {url}.md) so retrieval systems can ingest the content without an HTML parser — a practical convention endorsed by the llms.txt proposal but not yet formally consumed by any major answer engine.