An online stopwatch counts up from zero and lets you mark the moments that mattered. This one shows minutes, seconds, and hundredths until the run passes an hour, and then it shows hours as well. Start begins the count. Pressing start again stops it and leaves the time on the display so you can read it. Start after a stop continues from that time rather than jumping back to zero. Reset is the control that returns the clock to 00:00.00 and clears the lap list. The buttons do those three jobs. The keyboard does the same jobs when focus is not inside a field: Space starts and stops, L marks a lap, and R resets. Space is prevented from scrolling the page while it is used as the start key.
A lap is a row, not a second clock. The row shows the lap number, the split since the previous lap, and the elapsed time at the instant you marked it. The first lap's split is the whole time so far, because there was no earlier mark. Later splits are the gaps. You can mark a lap while the clock is running, or after you have stopped, as long as the clock is not still at zero. Marking a lap does not pause the count. If you need the clock to freeze, stop it. The list grows downward in the order you marked. Reset throws the list away with the time. There is no export and no account, because a lap on a kitchen timer does not need a spreadsheet unless you copy it yourself.
The digits are drawn as text, updated on the animation frame while the stopwatch is running. Hundredths are a display, not a laboratory instrument. A browser tab can be late by a frame, and a laptop that is saving power can be later. For a race that needs an official clock, use the official clock. For a speech, a set of study intervals, or a workout you are timing yourself, the hundredths are enough to compare laps. Leaving the tab in the background is the usual way these pages drift: browsers slow timers you cannot see. Keep this tab open if the last second matters. The page does not play a sound. If you wanted a beep at the end of a fixed length, that is the online timer, including the 5 minute timer.
Fullscreen asks the browser to give the digit stage the screen. The button toggles that state. Some browsers, and some embedded views, refuse the request. The note under the buttons says so, and the stopwatch keeps running in the page at its normal size. Esc leaves fullscreen in browsers that use that key. The stage is the digits, not the whole article, so the explanation below stays where it was when you return.
This is not a countdown. It will not alarm at five minutes, and it will not loop. Set a length on the timer when the task is "stop when this reaches zero." Use the stopwatch when the task is "how long did that take, and how did the parts compare." A metronome is a third thing: the metronome clicks at a tempo you choose, and it does not accumulate laps. People land on a stopwatch page from practice rooms and from kitchens for that reason. The directory is the list if you wanted a different tool.
Nothing is uploaded. The time lives in the tab. Refreshing the page resets it, which is the same as pressing reset, and there is no history to recover. That is deliberate. A stopwatch that remembered every lap from last week would need an account this site does not have. Read the laps before you leave. If a key seems dead, click the page background once so focus is not sitting in another control, then try Space again.