Networkversion v1.0.0

IP / CIDR Calculator

Every answer a subnet calculator is opened for — network, broadcast, netmask, wildcard, usable range and the exact number of hosts — for one IPv4 or IPv6 block. A /64 holds 18,446,744,073,709,551,616 addresses, which is larger than Number.MAX_SAFE_INTEGER, so the arithmetic here is BigInt from end to end and the count is exact rather than rounded to the nearest few hundred.

Address or block

Examples

Read this once

A private address range is not a security boundary. 10.0.0.0/8 being “internal” is a routing fact, not an access-control one.

And ::ffff:10.0.0.1 is not inside 10.0.0.0/8: it is an IPv6 address, so the membership check refuses it by name rather than answering. Libraries that silently unwrap that mapping are how an internal-range allowlist gets bypassed by a client arriving over IPv6 on a dual-stack socket.

Privacy

This page calculates in this browser tab. Nothing you type is sent to the server, stored, or written to the URL — an addressing plan is topology, and topology does not belong in a history entry or a CDN log.

No local storage, no analytics, no history entry. The honest asymmetry: the browser is local, the curl path is not. The terminal path calculates in memory and never writes or logs a body, but it is still a network request.

From the command line

The same URL answers a POST with an eleven-line record — one value per line, always eleven lines, so sed -n 4p is the broadcast address on every input. ?out= selects one field, and ?contains= answers a yes/no question in the exit status.

$printf '192.168.1.130/26' | curl -fsS --data-binary @- 'https://tools.primeforge.app/cidr'

$printf '192.168.1.130/26' | curl -fsS --data-binary @- 'https://tools.primeforge.app/cidr?out=hosts'

$if printf '10.0.0.0/8' | curl -fsS --data-binary @- 'https://tools.primeforge.app/cidr?contains=10.4.5.6' >/dev/null; then echo internal; fi

One block per request, on one line. A list is one word away: xargs -n1 -I{} sh -c "printf {} | curl …" — a record whose line count depended on the number of inputs would stop being a record.