My tarsnap helper scripts.
tarsnap_completion
A set of bash completions. Either drop it in your equivalent of /etc/bash_completion.d/, or source it some other way.
check_tarsnap
Nagios plugin which works by reading a text file containing a Unix timestamp of the most recent tarsnap backup. See the top comment in check_tarsnap for an example on how your tarsnap backup script can generate such a file.
tarsnap_usage
This Munin plugin keeps track on how much data a machine has backed up on tarsnap. This is done by reading the current amount of data from a text file, preferably updated by the tarsnap backup script. See the plugin documentation for details.