It works for me now. It checks if any other domains have been registered to trick people into thinking it's your website.
For example, I put in one of my websites (https://packetlosstest.com), and it gives the following:
Domain IPs HTTP banner WHOIS
packetlosstest.arab 127.0.53.53
packetl.osstest.com 54.161.222.85
34.205.242.146
packelosstest.com 103.224.182.210 Apache/2.4.38 (Debian) Domain Name: PACKELOSSTEST.COM
Registry Domain ID: 2659396158_DOMAIN_COM-VRSN
Registrar WHOIS Server: whois.dynadot.com
Registrar URL: http://www.dynadot.com
…
packetlos.stest.com 59.110.61.108 nginx
packetlo.sstest.com 54.161.222.85
34.205.242.146
packetlosstest.com 34.196.254.27 Netlify Domain Name: PACKETLOSSTEST.COM
35.229.48.116 Registry Domain ID: 2374572514_DOMAIN_COM-VRSN
Registrar WHOIS Server: whois.namesilo.com
Registrar URL: http://www.namesilo.com
…
The last one is my actual site, and the other five are apparently scammers preparing to impersonate me.