Tools built for engineers
Fast, accurate, ad-free utilities for networking and IT work: subnetting, security, DNS, and more. Most tools run entirely in your browser; the DNS and IP tools use outside services, explained in our Privacy Policy.
IP Subnet Calculator
Calculate network address, subnet mask, broadcast, CIDR range, and usable hosts for IPv4 and IPv6.
Open tool SecurityPassword Generator
Generate strong, cryptographically random passwords and passphrases — nothing ever leaves your browser.
Open tool NetworkingDNS Lookup
Check A, AAAA, CNAME, MX, TXT, NS records for any domain — compared across Cloudflare and Google DNS.
Open tool NetworkingWhat Is My IP
See your public IPv4 and IPv6 address, ISP, approximate location, and browser details instantly.
Open tool NetworkingWildcard Mask Calculator
Convert prefix lengths and subnet masks to the wildcard masks used in Cisco ACLs and OSPF, and back.
Open tool NetworkingMAC Address Lookup
Identify the hardware vendor behind any MAC address using the IEEE OUI registry. Runs in your browser.
Open toolPort Checker
Check whether a specific port is open on a given host — useful for debugging connectivity issues.
Subnet Mask Cheat Sheet
Every CIDR prefix from /8 to /32 with its subnet mask, wildcard mask, and host count, plus when to use each.
Open guide GuidePrivate IP Ranges
The RFC 1918 ranges, CGNAT, link-local, and loopback explained, with examples and common mistakes.
Open guide Guide/24 Subnet Explained
255.255.255.0, 254 usable hosts, and how to split a /24 into smaller networks.
Open guide Guide/27 Subnet Explained
Thirty usable hosts in blocks of 32: all eight /27 subnets in a /24, and where they fit.
Open guide Guide/16 Subnet Explained
65,534 usable hosts and 256 possible /24s: how to plan a large address block.
Open guide GuideAll guides
Browse every NetCalcTools guide in one place.
Open guideWhy NetCalcTools?
NetCalcTools is a growing collection of free, focused utilities for network engineers, system administrators, students, and anyone working with IP addressing, DNS, or basic security hygiene. Every tool is designed to be fast, accurate, and free of clutter — no sign-up walls, no ads, and no accounts.
The subnet calculator, wildcard mask calculator, password generator, and MAC address lookup run entirely in your browser, so what you type is never sent to us. DNS Lookup sends the domain you query to Cloudflare and Google's public DNS resolvers, and What Is My IP asks third-party IP lookup services for your public address and approximate location. See our Privacy Policy for details on each tool.