CACAO Validator

All,  I have started work on a validator for CACAO playbooks [1]. I just have some simple rules in there for the meta data right now. I will be adding to it as I get time. This stand along tool (statically compiled) allows you to pipe CACAO JSON data into the tool and it will tell you if the data is valid.
I am open to any suggestions or comments, especially about the output that comes from the tool.
Example: cat testdata1.json
validator
# To get help  ./validator  help
[1] -  https://github.com/openplaybooks/libcacao/tree/master/cmd/validator
Bret