Work and rest rounds with beeps, round counts and total time left. It stays right in a background tab.
A workout is built from the boxes: a prepare countdown, then rounds of work with rest between them. Work, rest, prepare and rest between sets are in seconds. Prepare can be 0 to 600, work 1 to 3600, rest 0 to 3600 and rounds 1 to 99. On a phone the presets, the clock and Start come first and these boxes sit under Times, sets and sound. There you can also add up to 99 sets, with a rest between sets of 0 to 3600 seconds. There is no rest after the last round of the workout, and with sets, the rest between sets replaces the normal rest after the last round of a set. A rest of 0 leaves rest out, which is how an EMOM works: work 60, rest 0, rounds 10 gives ten back-to-back minutes. The whole workout cannot run longer than 99 hours. If a box holds something that is not a whole number in range, a short message names the box and Start stays off.
The preset chips fill the boxes: Tabata 20/10 × 8, 30/30 × 10, 45/15 × 10 and EMOM 60/0 × 10. A preset sets work, rest and rounds, and puts sets back to 1 with no rest between sets. It keeps your prepare time. A chip shows as chosen while the boxes match it. Tabata with the default 10 second prepare runs exactly 4 minutes: 10 seconds of prepare, 8 rounds of 20 seconds, and 7 rests of 10 seconds. Before you start, a line under the time says the total. While it runs the screen shows the phase name with an icon, the time left in the phase, round and set counts, and the total time remaining. The phase is told by its name and icon, not by colour.
With Play sounds on, a short beep sounds at 3, 2 and 1 seconds before a phase ends, a longer beep when the next phase begins, and three rising beeps when the workout is over. A phase of 3 seconds or less gets fewer countdown beeps, because there is no time for all three. The phase is worked out from the device clock each time the page redraws, never by counting ticks, so the screen is right after the tab sleeps. Sound is different: a browser may delay or block it in a background tab, and a locked phone may stop the page. Keep the tab in view for a workout, and the screen is kept on while it runs on browsers that allow it. If the tab slept across several phases, the page jumps to the right one and plays one beep.
The boxes and the sound choice are remembered in this browser, so the page opens with your last workout. A workout that is running is not saved: reloading or closing the tab ends it. The boxes are locked while a workout runs or is paused and unlock after Reset. Nothing you type is sent anywhere. Page visits are counted with Google Analytics, never your settings. The page announces each new phase to screen readers, not each second. It needs no connection once loaded.
Once the last work phase ends, the workout is finished, so a closing rest would only make you wait. A Tabata of 8 rounds of 20/10 therefore has 7 rests and, with a 10 second prepare, takes 240 seconds. If you want a rest at the end, add it to your cool-down.
EMOM means every minute on the minute: you do a set number of reps at the start of each minute and rest for what is left. Choose the EMOM 60/0 × 10 preset. It gives ten 60 second rounds with no rest phase, and the beeps mark each new minute.
Rounds are the work and rest cycles in a row. A set is one group of rounds. With 3 sets of 8 rounds, you get 8 rounds, a rest between sets, 8 more, another rest, and 8 more. Leave Sets at 1 if you do not need grouping.
The phase and time stay correct, but sound may be delayed or blocked in a background tab. For a workout, leave this tab in view. The screen is kept on while it runs, on browsers that support it.
Up to 99 hours in total, with rounds and sets each at most 99 and no single phase over 3600 seconds. In practice it is the browser tab that sets the limit: reloading ends the workout.