This tool utilizes npm-ls on the target project and parses its output.
This way the tool does not depend on libraries that are already part of npm.
All logic and analysis is done by npm itself, the output is just interpreted and used.
Sometimes npm-ls got hiccups - caused by individual broken project installation or bugs with npm.
Then, this tool may also read package.json files inside the node_module directory as an additional information source.
Expected transformations, assumptions and results are described here.