Network Security Toolkit
Work out IPv4 subnets from CIDR notation and validate SPF email records. Runs entirely in your browser.
How these fit together
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.