Stopwatch & Timer
Stopwatch with lap tracking and countdown timer with alarm.
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How It Works
The stopwatch uses performance.now() — a high-resolution monotonic clock —
combined with requestAnimationFrame for smooth display updates. Because the
elapsed time is computed as a delta from a reference timestamp (not by summing ticks),
timing stays accurate even when the tab is backgrounded or the frame rate drops.
The countdown timer alarm uses the Web Audio API to synthesize three short beeps directly in the browser — no audio files needed.
Related Tools
Frequently Asked Questions
How accurate is the stopwatch?
The stopwatch uses performance.now(), a high-resolution monotonic clock accurate to sub-millisecond precision. Displayed time is computed as a delta from a reference timestamp, not by summing ticks — so accuracy is maintained even if the tab is backgrounded or the frame rate drops.
Will the countdown timer alarm play if the tab is in the background?
Most browsers throttle or suspend JavaScript timers in background tabs, which can delay the alarm trigger. Keep the tab visible or prevent your browser from suspending it. The timer continues counting (the reference timestamp is preserved), but the alarm may fire a few seconds late.
Can I run the stopwatch and timer at the same time?
Yes — both run independently on the same page. Start the timer, then start the stopwatch; they use separate animation loops and do not interfere with each other.