Scan an SSH server
Point it at any SSH server and it reports what that server accepts, its host keys, ready-to-publish SSHFP records, and whether it is exposed to Terrapin.
What this does, exactly
It opens a connection, exchanges identification strings, reads the server's algorithm list, and asks for one host key per algorithm. Then it hangs up — before attempting authentication, so it leaves no failed login in that server's logs.
It refuses private, loopback, link-local and carrier-grade-NAT addresses, checks every address a name resolves to before connecting, and dials the address it checked rather than re-resolving. Rate limited to 15 scans an hour per source address.
Same thing from a terminal, with no browser involved:
ssh ssh.rocks scan github.com