About PrefixBench

PrefixBench is a free subnet calculator built for network engineers, cloud architects, and IT students. It runs entirely in your browser. No data leaves your machine.

Features

• Split/Join Designer: interactively divide and merge subnets with a visual tree
• VLSM Planner: specify host requirements and get optimally-sized, correctly-aligned subnets
• Cloud Modes: accurate host counts for AWS (5 reserved), Azure (5), GCP (4), and OCI (3)
• Export: CSV, Excel (.xlsx), JSON, clipboard copy, and shareable URLs
• Visual Block Map: proportional view of your address space allocation
• Dark Mode: easy on the eyes during late-night subnet planning
• Undo/Redo: Ctrl+Z / Ctrl+Y with 50-state history
• Binary/Hex View: toggle address display format

Why We Built This

Existing subnet calculators are either outdated (no cloud modes), limited (no VLSM), or have poor UX (no dark mode, no undo). We wanted a tool that covers the full workflow, from planning to export, with correct math and a clean interface.

Technical Details

• Built with Astro, React, and Tailwind CSS
• 100% client-side: no backend, no database, no tracking of your calculations
• Hosted on Cloudflare Pages (global CDN, free HTTPS)
• URL sharing uses LZ-string compression. Your subnet designs are encoded in the URL, not stored on a server.

Educational Content

We publish free networking guides:

• What is Subnetting?
• CIDR Notation Explained
• VLSM Subnetting Guide
• Subnet Cheat Sheet
• AWS VPC Subnet Planning
• Azure VNet Subnet Planning
• GCP VPC Subnet Planning
• OCI VCN Subnet Planning
• IPv6 Subnetting Basics

Contact

Questions or feedback? Email hello@prefixbench.com