About SubnetKit
A fast, clean subnet calculator and networking reference, built for people who reach for one many times a day.
Why it exists
Most subnet calculators feel like they were built in 2004 and never touched again. They reload the page when you press calculate, bury the answer under banner ads, and hide the binary and wildcard behind extra clicks. SubnetKit is the opposite: type an address and every result appears at once, updating on each keystroke, with nothing in the way.
How it works
Every calculation runs as plain JavaScript in your browser. There is no server doing the maths, which means two things: it is fast, because there is no network round trip, and it is private, because nothing you type ever leaves your device. The reference pages for each CIDR prefix and port number are generated at build time, so they load instantly too.
What is here
The home page is the main subnet calculator. Beyond it are focused tools for CIDR, subnet masks, wildcard masks, supernetting, and IPv6, plus a full CIDR cheat sheet, a port reference, plain-English guides, an embeddable widget, and a free JSON API.
How it stays free
There are no paywalls and no sign-ups. Every calculator and reference page is free because the whole point is to be the tool you keep in a browser tab, not a funnel. SubnetKit may show display ads to help cover hosting and keep building new tools; if it does, they never sit between you and a result and never block a calculation. If it saves you time, a link from your blog, wiki, or README is the best thanks we could ask for.