HailBytes Engineering Toolkit

Free subnet/VLSM calculator, JWT decoder, hash, port lookup & firewall ACL tools for network and security engineers. 100% offline.

Free subnet calculator, VLSM planner, JWT decoder, port reference and firewall rule generator: 18 tools for network and security engineers in one click. 100% offline. No account, no tracking, and the extension makes no network requests. Stop juggling ad-filled calculator sites, and stop pasting production tokens into someone else's website. Everything here runs locally in your browser. ━━━━━━━━━━━━━━━━━━━━ NETWORK ━━━━━━━━━━━━━━━━━━━━ • Subnet Calculator: network, broadcast, mask, wildcard, usable range. Accepts 10.0.0.0/22 or 10.0.0.0 255.255.252.0, and handles /31 (RFC 3021) and /32 correctly • VLSM Calculator: plan subnets from any base network, largest-first, with overflow warnings • CIDR Range Expander: list the addresses in a block with network and broadcast labels • IP Address Converter: convert between dotted, decimal and hex, and see whether an address is private, loopback, link-local, carrier-grade NAT or public • Bandwidth Calculator: transfer time to required Mbps/Gbps, with headroom • DNS Record Reference: what each common record type does, with an example zone entry and typical use • Right-click any IP on a page → "Calculate subnet" ━━━━━━━━━━━━━━━━━━━━ SECURITY ━━━━━━━━━━━━━━━━━━━━ • JWT Decoder: paste a token or a whole Bearer header line to see its header, claims and when it was issued and expires, decoded locally. The token is never uploaded • Network ACL Generator: one form → Cisco IOS (with wildcard masks), iptables, nftables and AWS Security Group JSON • Ports Reference: 60 common ports, with a warning on the ones that are risky to expose to the internet, such as remote desktop and databases • Security Headers Generator: a recommended set of HTTP security headers in strict, moderate and API profiles • Password Strength Checker: breach-list, leetspeak, keyboard-walk and year detection, with offline crack-time estimate • Hash Generator: SHA-256, SHA-1, MD5 • Base64 encoder and decoder, URL parser, and a Unix timestamp converter that reads timestamps or dates and shows how long ago or how soon they are ━━━━━━━━━━━━━━━━━━━━ CLOUD ━━━━━━━━━━━━━━━━━━━━ • AWS EC2 Cost Estimator: monthly and yearly on-demand cost • Kubernetes Resource Calculator: CPU and memory totals and node count (CPU- or memory-bound) • Multi-Cloud Reference: AWS, Azure and GCP compute, storage and database services ━━━━━━━━━━━━━━━━━━━━ BUILT FOR LOCKED-DOWN WORKSTATIONS ━━━━━━━━━━━━━━━━━━━━ ✓ No account, no sign-up, no ads ✓ Makes no network requests; nothing you type leaves your browser ✓ Two permissions only: storage (your settings) and context menus (right-click subnet) ✓ Open source: github.com/hailbytes/engineeringtoolkit ✓ Picks up where you left off: inputs and results survive closing the popup (passwords and tokens are never saved) ✓ Keyboard-first and screen-reader friendly: / or Ctrl+K to search, arrow keys or 1/2/3 to switch tabs, Enter to run ✓ Light and dark themes · Chrome, Edge, Brave and Firefox ━━━━━━━━━━━━━━━━━━━━ FROM THE TEAM BEHIND HAILBYTES ASM AND SAT ━━━━━━━━━━━━━━━━━━━━ This toolkit is free because we build security platforms for the engineers who use it: • HailBytes ASM (attack surface management): continuously discovers subdomains, open ports, exposed services and vulnerabilities across your perimeter. • HailBytes SAT (security awareness training): phishing simulations and training for your whole team, with audit-ready completion certificates. Both run inside your own AWS or Azure account and have a 30-day free trial on the AWS and Azure Marketplaces. Learn more at hailbytes.com. Questions or ideas? hailbytes.com/contact