What this is
A set of webmaster tools, free to use, with no account and no payment. There is no contract here and nothing is being sold.
What the answers are worth
Most of what you see comes from somewhere else: registries, DNS, reputation services, ranking estimates, search engines. This site passes on what they said at the moment it asked. It does not check whether they were right, and it cannot.
The safety check in particular is three independent opinions that do not always agree. A clean result is not a guarantee that a site is safe, and a warning is not proof that it is not. Where a service did not answer, the page says so rather than treating silence as a clean bill of health.
Cached answers are shown with their age. An answer from two days ago describes two days ago.
Fair use
There is a per-address rate limit. It is generous for a person and restrictive for a script, which is the intent: this site reaches other people's services on your behalf, and their patience is a shared resource. Do not automate against it, and do not use it to probe systems you have no business probing.
The catalog
Domains added to the catalog are public and refreshed on a schedule. Add a domain only if you are content for it to appear on a public list.
No warranty
The site is provided as it is. It may be unavailable, it may be wrong, and it may change. Decisions that matter should not rest on it alone.