PageSpeed is a simple gem which ports Google Page Speed's scores to your command line.
Simply install the gem:
gem install page_speed
You have to get your API key first through here, then set it to the gem:
page_speed -k YOUR_KEY
After that, just execute page_speed against any website you can imagine:
page_speed URL
If we test it against itnig.net:
> page_speed itnig.net
Google Page Speed for itnig.net: 94 (Desktop) / 88 (Mobile)
If we test it against a non-valid URL:
> page_speed cucamonga
There has been an error. Please check your URL.