It's just like every other pomodoro timer website but with one spectacular improvement: time extensions. If you ever feel like you want to keep working or keep taking your break when the timer hits, you can choose to extend it. Simple as that.
When you do extend the time, it'll still keep the 10:3 work-to-break ratio by adding more time to your next work/break session. For example, if you decide to do 2 work sessions in a row, you have skipped 1 short break and so if you decide to take a break, the minutes from all your previously skipped breaks will be added to the current one.
The Pomodoro Technique is a time management method developed by Francesco Cirillo in the late 1980s.
Basically:
Work for 25 minutes
Take a break for 5 minutes
Repeat steps 1-2 2 more times
Work for 25 minutes
Take a break for 15 minutes
Repeat