Ask HN: Which internet/website blocker do you use to stay focused?

I find it a bit hard to stay concentrated when I know that procrastination is just one new-tab away. Currently I use Cold Turkey to help with that, but always wanted something more customizable. As such, would like to know what the good folks of HN use!

(Btw, if anyone knows of a internet/website blocker which has an API or similar that would be amazing. Ideally, I'd like to chain my time-tracker to it so that it only enables select websites after I invested X time for something productive.)