IP / CIDR calculator

IPv4 and IPv6 CIDR math — network, broadcast, usable host range, netmask, total hosts, and address classification.

/tools/ip-cidr takes any CIDR block — 10.0.0.0/16, 2001:db8::/48, 192.168.1.5/27 — and returns:

Network address and broadcast (IPv4) / last address (IPv6).
First and last usable host.
Netmask in dotted-decimal (IPv4) and prefix length.
Total host count, computed with BigInt — no overflow on /8 IPv6 ranges.
Address classification: Private (RFC 1918), CGNAT (100.64/10), Multicast, Loopback, Link-local, Documentation, Unique-Local (IPv6 fc00::/7), Public, etc.

IPv6 parsing handles :: compression both ways: input accepts shorthand, output shows the canonical RFC 5952 form (lowercase, longest zero-run collapsed). Runs in your browser — no network call, no input ever sent to a server.