The domain itself
The registrar you renew with, when it was registered, when it expires and how long that leaves, and whether it is locked against being moved without your say-so.
What a WHOIS lookup tells you
Every domain has a public record held by the registry that runs its ending, and public DNS records that say where it points. Together they answer the questions people ring us about: who do I pay for this, when does it run out, who is actually hosting my website, where does my email go, and can somebody else send email pretending to be me. We read both and explain them in plain English.
Where it all lives
Who hosts the website, who handles the email and who runs the DNS, named where we recognise them. Useful when you have inherited a site and nobody can remember who set it up.
Can anyone forge your email?
Whether SPF and DMARC are set up. Without them a stranger can send invoices that appear to come from your address, and your customers have no way to tell.
What we do not show
We never show a registrant's name, address, telephone number or email address, even where a registry publishes them. The owners of domains are people, and this is a utility for looking after your own domain, not a list for anyone to sell from.