Free tools
Small utilities we use ourselves. The calculators run entirely in your browser and there are no cookies. DNS and MX lookups go through our server, which keeps each answer for 30 seconds and nothing else.
Uptime and downtime calculator
Turn an uptime percentage into minutes of allowed downtime, or the other way round. Per day, week, month, quarter and year.
IPv4 subnet calculator
Network, broadcast, first and last host, mask, wildcard and usable hosts for any CIDR block or address and mask.
IP range to CIDR converter
Turn a first and last IPv4 address into the shortest list of CIDR blocks that covers exactly that range.
Subnet size by number of hosts
Enter how many devices you have and get the smallest subnet, mask and prefix that fits them.
Subnet splitter
Divide a network into 2, 4, 8 or more equal subnets and see the range of each one.
VLSM calculator
Give each department a subnet of the size it needs, with no overlaps and little waste.
CIDR aggregation
Combine a list of networks into the fewest blocks that cover the same addresses.
Is this IP in the subnet?
Check whether an IPv4 address belongs to a network written in CIDR form.
IPv6 subnet calculator
Network, last address, number of addresses and /64 subnets for an IPv6 prefix.
DNS lookup
Look up the A, AAAA, MX, TXT, NS, CNAME, SOA and CAA records of any domain, with their TTL.
MX lookup
Find the mail servers of a domain in the order senders try them, with their IP addresses.