The pomodoro technique fails for most people at the same point: the timer lives in an app you have to open, and opening it is the bit you skip when you’re already behind. Here, there’s nothing to open.

Twenty-five on, five off, fifteen after every fourth round. Not arbitrary numbers, twenty-five is short enough that starting doesn’t feel like a commitment, and four rounds is roughly where attention gives up regardless of how the day is going.
All four are editable. The useful change is usually upward. Fifty and ten for work that takes a while to get into. Change them after a week of the defaults, though, not before.
Phases can roll straight into the next one. Sounds like a minor convenience. It’s the setting that decides whether the technique survives a real day.
Off, every break ends with a decision to start again, and some of those decisions go the other way. On, the focus block has already begun by the time you look up. Work becomes the default and stopping takes a deliberate act.

A phase ending is useless information if you’re looking at a different tab. Which you’ll be, because the whole point is that you’re working. Hence a sound.
You can turn it off, and in a shared room you’ll. At which point the timer becomes something you check rather than something that tells you. That’s a real loss, and worth knowing before you decide the widget isn’t working for you.
It tallies completed focus blocks. Four before lunch is a good morning stated as a number rather than a feeling, and a far better measure of a day than hours at a desk, because it only counts time you actually spent on one thing.
Next to a task list it becomes a record: the list says what got done, the counter says what it cost.
The pomodoro timer widget is part of New Tab Studio — free to install, no account needed to start.
Add to ChromeThe timer belongs to the page. New Tab Studio is where you go between tasks, which is where the pomodoro cycle wants your attention anyway, but this isn’t a background timer that follows you around the browser.
All four. Focus, short break, long break, and how many cycles before the long one. Fifty and ten is the common alternative.
At the end of each phase, unless you turn the sound off. In a shared room you probably will, and the timer becomes something you check rather than something that interrupts you.
A countdown points at a date and stops. This cycles between phases on its own and keeps a count of how many you finished.
See the full widget catalogue or browse themes other people have built.