So I installed a tool globally via 'npm install beautify -g' The docs on the tool indicate a simple usage of 'beautify -o <output_file> <input_file>'
So I create an external tool whose PROGRAM is '/usr/local/bin/beautify' (I have confirmed this file exists, though it is a symlink to '/usr/local/lib/node_modules/beautify/bin/beautify.js') I have confirmed that from the Terminal I can type 'beautify' and Terminal finds it, and can confirm that '/usr/local/bin' is in my $PATH.
For PARAMETERS I've foregone using macros for the moment and just put: '-o ./sample/test.beautified.css ./sample/test.css' (I can confirm that from my project root, there IS a '/sample/test.css' file)
For WORKING DIRECTORY I used the macro: $ProjectFileDir$ which shows me as '/Users/<username>/Web/sites/<project_folder>'
However, when I right click a file in the PROJECT WINDOW and run the External tool on the file, my "RUN" window opens with an error:
'/usr/local/bin/beautify -o ./sample/test.beautified.css ./sample/test.css
env: node: No such file or directory
Process finished with exit code 127'
I took the first line and pasted it into a Terminal that was sitting at my project root and BOOM, the file was processed and it created the '/sample/test.beautified.css' file as expected. I can confirm that I setup my Node interpreter and enabled the Node.js Core Library as well. It shows me using 7.4.0 (which is correct), and shows 'beautify 0.0.8' installed and '0.0.8' as the latest.