How accurate is the stopwatch?

The stopwatch uses the browser's performance.now() API and requestAnimationFrame for smooth millisecond-level display. Actual timing accuracy is typically within a few milliseconds, which is sufficient for most everyday timing tasks.

Why doesn't the alarm sound on iOS?

iOS Safari requires a user gesture (tap or click) to unlock the Web Audio API. Make sure you start the countdown with a tap — do not rely on the page loading automatically triggering sound.

Does it keep running in the background?

The timer continues running when you switch browser tabs. The display updates when you return. However, if your device suspends the tab, timing may drift slightly.

Can I set a countdown longer than 99 hours?

The input fields support up to 99 hours, 59 minutes, and 59 seconds — a maximum of nearly 100 hours. For longer durations, a dedicated alarm app is more appropriate.

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Stopwatch & Countdown

Precision stopwatch with lap tracking and a countdown timer with alarm.

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关于此工具

A dual-mode timer tool featuring a full-featured stopwatch and a countdown timer in one clean interface. The Stopwatch tab offers millisecond-precision timing with Start, Stop, and Reset controls plus a Lap button that records split times in a scrollable list. The Countdown tab lets you set any HH:MM:SS duration, start, pause, and reset it, and plays an audible alarm using the Web Audio API when the timer reaches zero. Both modes feature a large digital clock display in a monospace font against a dark card for easy reading from a distance. No installation or account required — runs entirely in your browser.

使用方法

1 Select the Stopwatch or Countdown tab.
2 For Stopwatch: click Start to begin, Lap to record a split, Stop to pause, Reset to clear.
3 For Countdown: enter hours, minutes, and seconds in the fields.
4 Click Start on the Countdown tab and an alarm will sound when it reaches zero.
5 Use Pause to temporarily halt the countdown and Resume to continue.
6 Reset clears the timer back to the entered duration.

关于此工具

使用方法

常见问题