Network address, broadcast address, host range and host count for an IPv4 address + CIDR prefix.
For prefixes /30 and shorter, the first address in the range is reserved as the network address and the last is reserved as the broadcast address, so usable hosts = total addresses − 2. For /31 and /32, all addresses are shown as usable (point-to-point / single-host conventions).
The subnet mask (e.g. 255.255.255.0) marks the network bits as 1s and host bits as 0s. The wildcard mask is its bitwise complement — host bits as 1s — and is the form used in some router ACL and OSPF configurations.
It checks the IP against the three reserved private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) and the 127.x.x.x loopback block; anything outside those is labeled Public, regardless of whether that address is actually routed on the internet.