This tool is built to consume the overview-json output of the puppet preview tool
You must first generate a report using preview.
sudo /opt/puppet/bin/puppet preview --preview-environment future_production
--migrate 3.8/4.0 --nodes nodes.txt --view overview-json >overview.json
Then clone this repo and install the markaby gem. This must be done on the same system as you used to generate the preview report as we read the code of disk as well as load the indivdiual nodes catalog_diff.json files for the report.
/opt/puppet/bin/gem install markaby
sudo ./preview_report.rb -f overview.json -w /vagrant/example.html