It goes in a JSON file for Node because there's already one present to configure NPM packages, just as for Ruby applications you can define the runtime in your

It goes in a JSON file for Node because there's already one present to configure NPM packages, just as for Ruby applications you can define the runtime in your Gemfile. In the Python world their package manger uses a file called something like "packages.txt", and so runtime.txt makes some sense alongside that.