where are all the IPv6 tools?

A while ago I was having some conceptual barriers dealing with
sanity-checking a given IPv6 network specification, e.g.,
why are


valid but 2620:0:510::/41 not valid? So I coded up something
that would offer a bit of an explanation:

  checknet 2620:0:510::/41
  The network prefix has more bits than the prefix size:
  This is the rightmost non-zero hex digit for a /41 prefix.
  If non-zero, the digit must be an 8.

Otherwise, the tool the quite basic compared to the others
that were mentioned.