WWW CNAME properly configuredWhat it checks and how to fix it

What it checks

Resolves the www counterpart of the audited host, or the bare domain when the site is served on www. Passes when it resolves through a CNAME or an A record, and warns when it has no record or does not exist.

Why it matters

Plenty of people type www in front of a domain, or leave it out, and links in the wild use both forms. If the other form does not resolve, those visitors get a browser error instead of your site and the backlinks pointing at it are lost. Resolving both forms is also what makes it possible to redirect one to the other.

How to fix it

Point www at the bare domain (or at your hosting provider's hostname) with a CNAME:

www.example.com.  3600  IN  CNAME  example.com.

The bare domain cannot be a CNAME. Give it A/AAAA records, or use your provider's ALIAS / ANAME record or CNAME flattening (Cloudflare flattens a CNAME at the apex automatically):

example.com.  3600  IN  A  203.0.113.10

Then make sure the certificate covers both names and redirect one form to the other (see the WWW redirect check).

dig +short www.example.com