Network Security Toolkit

CIDR Calculator takes an IPv4 address in CIDR notation (192.168.1.0/24) and computes the subnet mask, network and broadcast addresses, the usable host range, and how many hosts actually fit — with a binary breakdown showing exactly which bits are network and which are host. On the email side, SPF Record Parser breaks down an SPF TXT record into its mechanisms and qualifiers, counts how many of the 10 allowed DNS lookups it uses, and flags common mistakes like +all or a missing all. For a website's own defenses, Security Headers Analyzer scores CSP, HSTS, X-Frame-Options, Referrer-Policy, and Permissions-Policy from raw response headers, with recommendations for each one that falls short. Carving up a larger block for multiple departments or sites instead of a single subnet? VLSM Subnet Calculator allocates a differently sized subnet for each host-count requirement from one base network.