A CIDR block (e.g. 192.168.1.0/24) describes an IP network with a prefix length denoting how many leading bits are fixed as the network portion — the rest are host bits. This tool computes the network and broadcast addresses, the usable host range, and the total/usable host counts purely from the address and prefix you enter, entirely in your browser.
/31 networks (RFC 3021) are a special case used for point-to-point links: both addresses are usable as hosts, since there's no room for a separate network/broadcast address. /32 describes a single host.
What do network and broadcast addresses mean?
The network address is the first address in the block (all host bits zero) and identifies the subnet itself; the broadcast address is the last (all host bits one) and is reserved for broadcasting to every host on the subnet.
Why do /31 and /32 behave differently?
/32 describes a single host with no room for a network or broadcast address. /31 (RFC 3021) is a special case for point-to-point links where both addresses in the 2-address block are usable as hosts.
Does this tool look up who owns an IP range?
No — it only computes the subnet math for the CIDR block you type in; nothing is looked up or sent anywhere.