Custom intervals
Runs in your browser, nothing to install. Space bar starts and pauses. It keeps time against the clock rather than counting frames, so a backgrounded tab does not make it drift — but a phone that sleeps will still stop it, which is the one thing the app fixes.
Tabata
The original protocol: 20 seconds all-out, 10 seconds rest, 8 rounds. It is conventionally called a four-minute workout, which counts a rest after the final round — the timer above ends on the eighth work interval, so it runs 3:50. Either way it is genuinely hard at true maximum effort, and the tell that you are not actually sprinting is being able to hold the same pace across all eight rounds.
Sprint intervals
Three sessions a week of 3×20-second all-out sprints — about 10 minutes of work per session — produced cardiometabolic adaptations comparable to 150 minutes per week of moderate continuous exercise.
- Gillen et al., PLOS ONE, 2016. View study ↗
What the timer actually does
Fifteen built-in protocols including Tabata, Huberman HIIT, the 6-second cognitive interval and grip training, plus fully custom work/rest/round counts. A boxing clapper ten seconds before work ends, a five-second countdown into each work phase, optional spoken cues, and an optional warm-up that counts down first and is excluded from your logged minutes. It pairs with a Bluetooth heart-rate strap if you have one.
It works offline
The whole app installs to your home screen and runs without a connection — useful in a gym basement with no signal. Nothing about the timer requires an account.