WWW to non-WWW (or vice versa) redirectsWhat it checks and how to fix it

What it checks

Requests the same URL on the other host form: www when the site is on the bare domain, or the bare domain when it is on www. Passes when that host redirects to the audited host or does not serve the page, and warns when both versions answer 200, when the redirect points to another host, or when the other form cannot be reached.

Why it matters

When example.com and www.example.com both serve the same pages, search engines see two copies of the site and split links and ranking signals between them, and analytics, cookies and sessions are split too. Picking one canonical host and permanently redirecting the other consolidates them.

How to fix it

Choose one host as canonical and permanently redirect the other to it, keeping the path. The redirecting host needs DNS and a valid certificate too.

# nginx
server {
  listen 443 ssl;
  server_name www.example.com;
  # ssl_certificate must cover www.example.com
  return 301 https://example.com$request_uri;
}

# Apache
<VirtualHost *:443>
  ServerName www.example.com
  # SSLEngine on + certificate covering www.example.com
  Redirect permanent / https://example.com/
</VirtualHost>

# Rails: config/routes.rb
constraints(host: "www.example.com") do
  get "(*path)", to: redirect(host: "example.com", status: 301), format: false
end

Cloudflare: Rules → Redirect Rules → create from the "Redirect from WWW to root" template (or the reverse), and make sure the www DNS record exists and is proxied.

curl -sI https://www.example.com/