High-Precision Stopwatch
Millisecond-accurate monotonic timing with lap splits, average variance analysis, CSV export, and keyboard shortcuts.
Private by architecture:
All processing is 100% client-side memory. Your data never leaves this browser tab.
00:00.000
Shortcuts:
Space Start / Pause L Record Lap R Reset
Laps 0
Avg Lap 00:00.000
Fastest None
Slowest None
No laps recorded yet. Press Lap (L) while timing to capture split times and delta variances.
About This Tool
Standard JavaScript Date-based timers are prone to system clock adjustments and throttling. This stopwatch uses performance.now(), which provides sub-millisecond monotonic timestamps that measure elapsed time continuously without drifting or warping during OS clock synchronizations.
Record intermediate splits and analyze performance at a glance. Every recorded lap displays individual split duration, total elapsed time, variance from the average lap, and visual highlights for your fastest and slowest intervals.
Key Features
- Monotonic performance.now() accuracy: Measures elapsed time using high-resolution hardware timestamps that do not drift with system clock updates.
- Lap splits and cumulative totals: Inspect individual interval durations alongside cumulative session time in a clean, high-contrast table.
- Fastest and slowest lap detection: Instantly identifies your peak performance intervals and variance from your overall average.
- CSV export: Download full session lap data directly to CSV with one click for analysis in spreadsheets.
- Full keyboard navigation: Control your timing session completely hands-free using Space to start/pause, L to record laps, and R to reset.
Frequently Asked Questions
How accurate is this stopwatch compared to physical stopwatches?
Because it relies on the browser performance.now() high-resolution monotonic timer, it calculates intervals with millisecond accuracy, unaffected by computer clock synchronization or time zone adjustments.
What happens if I switch tabs while the stopwatch is running?
The timer continues running accurately. When you return to the tab, the display updates immediately to the true elapsed interval calculated from the start timestamp.
What keyboard shortcuts are supported?
Press Space to start or pause, L to record a lap, and R to reset the timer to zero.
Is any session or lap data saved on a server?
No. All timing calculations and lap logs remain strictly in your browser memory and are deleted when the page is closed.
