Stopwatch & Countdown Timer

How the stopwatch and countdown timer work

Switch between Stopwatch and Countdown at the top; the timer resets when you change modes. The large reading is driven by a monotonic clock, so it stays accurate even after the tab was in the background.

• Stopwatch: press Start, then Lap for each split. Every row shows the split and the running total, and the fastest and slowest laps are badged.
• Countdown: pick a preset or type your own duration, then start. A short beep plays when it reaches zero.
• Custom duration: accepts plain seconds (90), clock form (1:30, 0:05:00) and unit form (5m, 1h30m, 1分30秒).
• Keyboard: Space starts or pauses, L records a lap, R resets.
• Reminders: when a countdown reaches zero it beeps, flashes the tab title, and — if you allow notifications — sends a desktop alert that you can silence with one click.

Lap results can be copied as tab-separated text. The last mode and duration, and copied laps, are only stored on this device when "remember tool data" is enabled.

Everything runs locally — no account, no upload, and no network request while the timer runs.