IPv6 shows network, prefix, first/last address, and address count when the range is modest; huge prefixes are summarized without enumerating every host.
Last successful CIDR restores on return · this browser only (localStorage)
IP in subnet
Paste an address and check membership against the CIDR above. Same family only (IPv4↔IPv4 or IPv6↔IPv6).
nginx / ACL snippets
Copy common allow/deny patterns for the CIDR above. Order matters in nginx allow/deny — review before paste.