/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.