What it does
For your site to work at both example.com and www.example.com, DNS has to point both names at your server, and the server has to redirect one to the other. Get either wrong and some visitors get an error, or search engines see two copies of your site.
This tool checks both. It looks up A, AAAA and CNAME records for both names through Cloudflare's public resolver, 1.1.1.1, over DNS-over-HTTPS. Then it opens http and https for each name and follows the redirects.
How to use it
- 1Enter your domain in Domain. Either form works; the bare domain and www are both checked.
- 2Press Check DNS and www.
- 3Read the records table. Each name needs at least one A, AAAA or CNAME record; a name showing none won't load.
- 4Check the redirects and findings. If every version ends on one address, the tool names it as your canonical host.
The records that matter here
DNS doesn't allow a CNAME on the bare domain, because a CNAME can't sit alongside the NS and other records the apex needs. Many providers offer CNAME flattening, ALIAS or ANAME instead, which answer with A and AAAA records.
- A: points a name to an IPv4 address.
- AAAA: points a name to an IPv6 address. Optional, but it has to work if you publish it.
- CNAME: makes a name an alias of another, common for www pointing at a CDN or host.
Choosing www or non-www
Neither ranks better. Pick one, make sure both names resolve, redirect the other with a 301 or 308, and use your choice in canonical tags, the sitemap and internal links.
DNS answers are cached for each record's TTL, so a change can take minutes to hours to reach everyone. If the result looks wrong right after a change, wait for the old TTL to pass and check again.
Questions
Why does www show no records?
No record was created for it. Add a CNAME for www pointing at your host, or an A record matching the bare domain, then redirect it to your canonical host.
Which DNS server does this use?
Cloudflare's 1.1.1.1, through DNS-over-HTTPS. It shows what a public resolver sees, which can differ from your local network's cache.
Does it check MX, TXT or other records?
No. Only A, AAAA and CNAME for the domain and www, the records that decide whether a browser can reach the site.
Does serving both www and non-www hurt SEO?
Without a redirect, search engines have to pick one and links may be split between them. A permanent redirect and matching canonical tags settle it.