This tool reports ip address ranges for a collection of CIDRs, and then reports if there is any overlap.
The official package name is mcquay.me/cidr.
# prints range
$ cidr 10.0.0.0/24
10.0.0.0 10.0.0.255 256
# range plus no error for overlap:
$ cidr 10.0.0.0/24 10.0.2.0/24
10.0.0.0 10.0.0.255 256
10.0.2.0 10.0.2.255 256
# error on overlap
$ cidr 10.0.0.0/24 10.0.0.5/32
10.0.0.0 10.0.0.255 256
10.0.0.5 10.0.0.5 1
overlaping networks: 10.0.0.5/32 overlaps with 10.0.0.0/24
$ cidr 10.0.1.0/24 10.0.0.0/16
10.0.1.0 10.0.1.255 256
10.0.0.0 10.0.255.255 65536
overlaping networks: 10.0.1.0/24 overlaps with 10.0.0.0/16