Babel 6.0.2 slowness reproduced on Ubuntu 14.04 using only node 4.2.1 and npm 2.14.7: $ uname -v #94-Ubuntu SMP Thu Jun 18 00:27:10 UTC 2015 $ node -v

Babel 6.0.2 slowness reproduced on Ubuntu 14.04 using only node 4.2.1 and npm 2.14.7: $ uname -v #94-Ubuntu SMP Thu Jun 18 00:27:10 UTC 2015 $ node -v v4.2.1 $ npm -v 2.14.7 $ npm install babel $ npm install babel-cli $ npm install babel-preset-es2015 $ node_modules/.bin/babel -V 6.0.2 (babel-core 6.0.2) $ echo "class Foo {}" | time node_modules/.bin/babel --presets es2015 2.49user 0.12system 0:02.58elapsed 101%CPU Compared to babel 5.8.23 on same Linux VM: $ babel -V 5.8.23 (babel-core 5.8.24) $ echo "class Foo {}" | time babel 0.58user 0.02system 0:00.57elapsed 106%CPU