Online Stopwatch

What does this online stopwatch do?

It counts up in hundredths of a second, records laps, and needs nothing installed. This free stopwatch from ÆON Toolhub starts with a click or the space bar, keeps the running time in the browser tab title so you can watch it from another tab, and can beep at a minute mark you choose. You can copy your laps, download them as CSV, or blow the display up to full screen for a wall.

Nothing is saved on a server. Everything happens in your browser and clears when you close the tab.

How do you use it?

Start. Press Start or hit the space bar. The display runs in mm:ss.cc, adding an hours field once you pass sixty minutes.

Record a lap. Press Lap or the L key at each segment. Every lap logs a split and a total.

Pause and resume. Space toggles both. Pausing keeps the elapsed time; Reset (or R) clears the clock and the laps.

Set an alert. Choose 1, 2, 5, 10, or 15 minutes and a beep fires when the stopwatch crosses it, with an optional desktop notification.

Go full screen. Fills the window with the time, for a gym, classroom, or lab display.

What is the difference between a lap and a split?

This trips up most people, and most stopwatches do not bother to explain it.

• Split is the duration of that one segment, measured from the previous lap.
• Total is the time since you pressed start.

So if you are timing a runner doing 400 metre repeats, lap three might show a split of 01:02.44 (that lap alone) and a total of 03:10.87 (the whole session so far). Both columns are shown here, side by side, so you never have to subtract in your head.

Can you keep your times?

Yes, and this is where a browser stopwatch usually fails you. The lap panel has Copy, which puts the whole table on your clipboard ready to paste into a spreadsheet, and CSV, which downloads the same data as a file. Laps export oldest first, each with its split and total, so the order matches how you recorded them.

The laps themselves are not stored between visits, by design. Closing the tab clears everything, so export before you leave if the times matter.

Are there keyboard shortcuts?

Yes, and on a stopwatch they matter more than on most tools, because you are usually watching something else at the moment you need to press the button.

They are ignored while you are typing in a field, so they never fight with the alert input.

Does it stay accurate in a background tab?

Yes. The stopwatch works out the elapsed time from a fixed start timestamp rather than counting frames, so it does not drift when the browser throttles an inactive tab. Switch away, come back, and the reading is the real elapsed time, not a count of how many frames the browser bothered to render. Browsers also throttle timers on battery saver, which is exactly the case this approach survives.

What do people use it for?

Workouts and interval training, cooking, timing a presentation rehearsal, tracking billable work, science and school experiments, timing laps on a track, and any "how long did that take?" question. The alert is handy when you want to be told at two minutes instead of staring at the screen, and full screen turns a laptop into a wall clock for a room.

Your data stays private

The stopwatch runs entirely client-side. No times, laps, or settings are uploaded, logged, or stored on a server, and everything clears when you close the tab. It also keeps working offline once the page has loaded.