Canonical tags are self-referencing and consistent

A canonical pointing to HTTP while the site serves HTTPS tells Google to index the insecure URL — which may not exist — and the page drops out of results. Conflicting canonical declarations (one in the layout, one in the page) force Google to pick arbitrarily, often choosing the wrong target. Cross-domain canonicals caused by copy-paste errors hand your ranking authority to the wrong host entirely.

Generate canonicals from a single source of truth such as NEXT_PUBLIC_SITE_URL so every page emits absolute HTTPS URLs. Remove any canonical declaration from layouts when pages also set one — keep it in exactly one place per route. Strip tracking and session parameters from the canonical value before rendering it.

// app/layout.tsx
export const metadata = { alternates: { canonical: `${process.env.NEXT_PUBLIC_SITE_URL}/current-page` } }