{
  "plugins": {
    "metalsmith-babel": {
      "modules": "common",
      "comments": true
    }
  }
}

var Metalsmith = require('metalsmith');
var babel = require('metalsmith-babel');

new Metalsmith('./source')
.use(babel({/* 6to5 options */}))
.build(function(err, files) {
  if (err) {
    throw err;
  }

  console.log('Completed.');
});