Work, rest, rounds: what the timer does
An interval timer alternates a work period and a rest period for a set number of rounds and tells you, by sound and colour, when each one changes. Here you set the work seconds, the rest seconds and the rounds; the timer adds a 10-second get-ready before the first round so you can take position, and you can add a warm-up before and a cool-down after, each skipped when set to 0. The rest after the final round is left out, so the session ends on work.
Before you start, the total time of the whole session is shown, get-ready included: 30/15 × 8 is 5 minutes 55 seconds. While it runs you see the current period in large letters, WORK in red or REST in green, the seconds left, Round 3 / 8, what comes next, and how much of the whole session remains.
The presets and where their numbers come from
The times in brackets are the rounds alone; the 10-second get-ready comes on top, and the preset chips show the sum. HIIT 30/15 × 8 (rounds 5:45) is the common 2:1 interval used on most timer sites and apps. Tabata 20/10 × 8 (rounds 3:50, 4:00 with the get-ready) is the protocol from Tabata's 1996 study, which has its own page here. 40/20 × 8 (rounds 7:40) is a gentler 2:1 variant that suits circuit stations. 45/15 × 10 (rounds 9:45) is the boot-camp standard, 3:1, for a longer burn. EMOM 60 × 10 (rounds 10:00) has no rest: you start a fixed set of reps every minute on the minute and rest for whatever is left of the minute. Boxing 3:00/1:00 × 6 (rounds 23:00) is the professional round and break length.
Choosing a preset only changes work, rest and rounds; your get-ready, warm-up and cool-down stay. Every combination has an address, so the one you use most can be bookmarked.
Choosing a work-to-rest ratio
The ratio sets the intensity more than the absolute numbers do. Beginners do well with rest equal to or longer than work: 20/40 × 6–8 or 30/30 × 8–10. Intermediate: 30/30 × 8–12 or 40/20 × 8–10. Advanced: 45/15 × 10–12, or Tabata's 20/10 × 8 at genuinely all-out effort. Those are the ranges most trainer guides agree on; if you cannot keep the work quality up in the last rounds, lengthen the rest or cut rounds rather than slowing the work.
A warm-up of 3–5 minutes and a cool-down of 2–3 minutes are worth adding when the session is the whole workout; set them to 0 when the intervals come in the middle of a longer session. Total time matters too: most interval workouts are 10–20 minutes of rounds, and more is rarely better.
Beeps, tones and the final alarm
Three short beeps mark the last 3, 2 and 1 seconds of every period, so you know a change is coming without looking, and a longer, higher tone sounds on the change itself; the get-ready ends with the same tone, which is your GO. When the last round finishes, the alarm sound you choose repeats until you stop it. The 3-2-1 beeps can be switched off in the alarm settings, and choosing None silences everything except the colours and the tab title.
The Cuckoo alarm is a clip of about 65 KB fetched once and the other sounds are synthesised in the browser; all are pre-scheduled on its audio clock, so they land on the exact second even when the page is busy or in the background. There is no voice announcement; the colours and beeps are designed to be enough from across a room.
On a phone and in the gym
Keep screen on is on by default on phones: the screen stays awake while the timer runs and is released when it stops, so a 10-minute session is not cut short by auto-lock. Press F for the full-screen view, which fills the display with the period colour, the seconds and the round, readable from the floor. Android phones vibrate at the end; on an iPhone keep the tab in front, since Safari pauses hidden pages, and iOS 17+ plays the beeps through the silent switch.
Timing does not depend on the screen: each period's end is fixed when it starts, so if you glance away or a notification covers the browser, the timer is still exactly on schedule when you look back.
Skip, back, pause and sharing a workout
Skip (S) ends the current period at once and moves on; Previous (B) restarts the current period, or jumps back to the one before if less than three seconds have run. Pause (Space) holds everything; Cancel (R) ends the session and returns to the settings. A skipped work round is not counted as completed, so the finish summary is honest about what you did.
Share link copies an address such as ?w=40&r=20&n=10&p=10 that opens the timer with the same settings anywhere; the old long form ?work=40&rest=20&rounds=10 is accepted too. A running session survives a reload: the page restores it and catches up if periods passed while you were away.
Interval timer, stopwatch, Pomodoro or plain timer?
Use this page for anything with repeating work and rest: HIIT, Tabata, circuits, EMOM, boxing rounds, sprint repeats. Use the stopwatch to time a run or a set and record laps. The Pomodoro timer is the same idea for desk work, with 25-minute focus and 5-minute break periods and a long break every four. The plain timer counts down one length and rings, for a plank hold or a rest between heavy sets.
All of them share the alarm sounds and settings, and all keep exact time in a background tab.