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Basics

Should I use www or non-www

Two hosts serving the same pages is duplicate content. Ranking signals and backlinks are divided between them, so both versions rank lower than the single canonical version would. Which one you pick matters far less than picking one.

What 13x checks

This is rule basics.www-consistency in the public registry: One canonical host (www or non-www). It runs on every audit, against the pages we actually fetched, and its result is derived from the response rather than estimated.

Surface
Basics
Score weight
6 of the readiness score
Scope
Runs on every audited page
Applies
To every site

Registry version 2026-07-30. Every rule is published, and the audit is deterministic — the same page produces the same finding every time.

The fix

The same text the audit hands you when this check fails on your own site.

Pick one host and redirect the other to it with a 301. Either direction is fine; what matters is that only one serves content.

On Vercel, set the preferred domain in Project → Settings → Domains and mark the other as a redirect. Then make sure your canonical tags and sitemap use the same host you chose — a redirect plus a canonical pointing at the other host reintroduces the split.

Does your site have this problem?

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