Setting the timer: type it, pick a preset, or nudge it by a minute
Enter hours, minutes and seconds in the three boxes, or tap a preset from 1 minute to 1 hour. The boxes also understand typed times: paste 1:30 for a minute and a half, 1:30:00 for an hour and a half, or 1h30m, and the timer sorts it into the right boxes. A number on its own in the minutes box means minutes, so 90 becomes 1:30:00. The longest timer is 99 hours 59 minutes 59 seconds.
The +1 min and −1 min buttons work before you start and while the timer runs, so a 10 minute timer can become 12 without stopping it. The display always rounds up: with 0.4 seconds left it shows 00:01, and 00:00 appears only when the alarm actually fires.
It keeps exact time when you switch tabs or lock your phone
The timer does not count screen updates; it stores the exact moment it should end and recomputes the remaining time from the clock every time it draws. Chrome slows background tabs down to one update per second, and after five minutes to one per minute, so timers that count ticks drift late by up to a minute. This one cannot drift, because a late tick simply shows the correct smaller number.
The alarm is scheduled three ways at once: a single system timer set to the exact end time, the alarm sound pre-scheduled on the browser's audio clock so it plays even if page scripts are throttled, and a desktop notification. When you come back to the tab, the page checks the clock immediately; if the time passed while the device was asleep, it shows how long ago and rings right away. On iPhone, Safari pauses pages that are not on screen, so keep the tab in front or leave the screen on; the Keep screen on option does that for you.
Alarm sounds, volume and repeat
Eight alarm sounds: Beep (three short 880 Hz tones), Bell (a struck bell with its overtones), Digital (a wristwatch-style chirp), Soft (a gentle rising chime), Cuckoo (a recorded cuckoo call), Chime (a door-chime ding-dong), Pipe (a two-note pipe call) and None. Cuckoo is a clip of about 65 KB fetched once and then kept by the browser (if it cannot load, Pipe rings instead); all the others are generated by the browser itself, so they play instantly and offline. Preview plays the sound once at the current volume.
By default the alarm repeats every 1.6 seconds (a longer sound such as Cuckoo right after each ring ends) until you press Stop alarm, Space or Esc, and stops on its own after 60 seconds so a forgotten tab does not ring all afternoon. Turn Repeat off for a single ring. Browsers only allow sound after you have tapped the page once; starting the timer counts, and if the page was restored after a reload a banner asks for one tap.
Using it on a phone
Keep screen on is switched on by default on phones. It asks the browser to hold the screen awake while the timer runs and releases it as soon as the timer stops, so the alarm is not lost to auto-lock. It works in Chrome, Edge, Firefox 126+ and Safari 16.4+; iPhone home-screen web apps need iOS 18.4.
On iPhone the silent switch mutes most web audio. On iOS 17 and later this timer asks for a playback audio session, which plays the alarm through the silent switch; on older iPhones turn the switch off before starting. Android phones also vibrate when the alarm fires if Vibrate is on.
What happens at zero
The display turns to 00:00, the background changes colour, the tab title flashes "Time's up", and a counter shows how long ago the timer ended (+00:12), which is handy when you only notice later. If the tab is in the background and notifications are allowed, a desktop notification appears; clicking it brings the tab forward and stops the alarm.
From the finished screen you can Restart the same length, or press +1 min to get one more minute immediately: the extra minute starts right away and rings again at the end. Cancel (R) returns to the time you set.
Sharing a timer and getting it back after a reload
Every length has a link: ?d=600 is ten minutes, and the preset pages such as /time/10-minute-timer/ are permanent addresses you can bookmark. While a timer runs, Share link also includes the exact end time, so a colleague who opens it sees the same countdown and hears the alarm at the same moment, in their own time zone.
A running or paused timer survives a reload and a closed tab: the page stores the end time on this device and restores it when you return. If it ended while you were away, you get a short notice with the time it finished; a timer that ended more than ten minutes ago is discarded so an old alarm does not go off unexpectedly.
Timer, stopwatch, countdown or Pomodoro?
A timer counts down a length you choose and rings at zero; this page. A stopwatch counts up from zero and records laps, for measuring how long something takes. A countdown shows the days, hours and minutes until a date, such as an exam or New Year. A Pomodoro timer alternates focus and break periods automatically, and an interval timer repeats work and rest rounds for training.
All five share the same clock engine, alarm sounds and settings, so a sound and volume chosen here apply everywhere, and each keeps exact time in the background the same way.