Countdown timer
Runs in your browser · keep this tab visible
Pick a length, press start, and it chimes at zero. Presets cover the common ones; the slider goes up to two hours.
How to use the countdown timer
The timing is read from a monotonic clock each frame rather than counted up by adding one second per interval tick. That distinction is invisible for two minutes and obvious over an hour: interval ticks are only approximately on time and their error accumulates, so a naively-built timer runs minutes late. Reading the clock directly means the display is right the instant you look at it, even after the tab has been in the background, though a backgrounded tab is throttled, so the chime itself can arrive late even when the number is correct.
Questions
No. The remaining time is calculated from a monotonic clock rather than by counting interval ticks, which is where drift comes from.
The number stays correct, but browsers throttle background tabs, so the chime may be late. Keep the tab visible if that matters.
Yes. Pause keeps the remaining time and resume carries on from there.
On a phone, generally not; the browser is suspended. Use the phone’s own timer for that.
Yes, there is a mute box. The display still shows when it finishes.
No. Nothing is stored, so a reload starts fresh.