SubNet Calc by Libor Benes

SubNet Calc is an essential tool for network planning, troubleshooting, and education, combining simplicity, accuracy, and privacy in a compact Firefox sidebar. Designed for network engineers, sysadmins, network analysts, and students to effortlessly calculate IPv4 (not IPv6) subnets.

Enter an IPv4 address, a CIDR mask, and the desired number of subnets => get instantly a table with detailed subnet information. Copy results, paste into network documentation or monospaced editors or spreadsheets. Tab-separated output aligns best in monospaced editors (e.g., Notepad++) or Excel; alignment in non-monospaced editors (e.g., Windows Notepad) or WPS Office may vary.

Security Prioritization:
• Minimal Design.
• Offline Operation: Performs all calculations locally, requiring no network access, ensuring privacy - no user data is collected, stored, or transmitted.
• Minimal Permissions.
• Safe Coding and DOM Manipulation.
• Adheres to Moz://a standards for Firefox add-ons, ensuring compatibility and security.
• Error Handling.

SubNet Calc relies on ipaddr.js, a lightweight, MIT-licensed JavaScript library (version 2.2.0, 13 KB) for parsing and validating IPv4 addresses. ipaddr.js is a part of the add-on's local codebase, no network connections, sourced from https://github.com/whitequark/ipaddr.js. ipaddr.js ensures accurate and safe IP address handling, enabling reliable subnet calculations and input validation.