What is compared
Both domains go through the same live lookup as the full domain report. The comparison then lines up, row by row: registrar, creation and expiry dates, status codes and the registry's DNSSEC flag; nameservers and the A, AAAA and CAA records; MX hosts, detected mail provider, SPF and DMARC records; the network (AS number), allocation country and CDN edge of the addresses, the Server header and the final URL; and the certificate issuer, its expiry date, the TLS version and HSTS.
Each row carries a label with an icon: same, different, or could not be checked. Lists are compared without regard to order or letter case, so two domains with the same nameservers in a different order count as the same.