Twenty-five minutes is the length people borrow from focus methods and then customise. Here it is only a countdown: 25:00, an alarm, and a fullscreen clock. If you want the matching five minute break, open the five minute timer when this one ends. The two pages do not talk to each other. This 25 minute timer opens the countdown at 25:00, which is 1,500 seconds, with an alarm at the end. You do not have to type the length. The fields are already filled. Start, pause, reset, and fullscreen are the same controls as the main online timer.
Press start and the display steps about ten times a second, while the end is computed from a timestamp so a tab that is briefly covered does not lose the whole minute. Pause keeps the remainder. Reset returns 25:00, not a blank zero you must fill in again. Fullscreen enlarges the digits. Three short beeps play when the remainder hits zero, as long as the start click has opened the audio context and the tab is still alive.
The length is not a promise about a recipe, a nap, or a lesson. A packet, a teacher, and your own body can disagree with 25 minutes. The page only counts. If a neighbour is a better fit, open 20 minute timer and 30 minute timer. The stopwatch counts up when the real question is how long something has already been going, not when it should stop.
The sound will not cross into another tab and it will not come back after you close this one. Browsers can also block autoplay until there is a gesture; the start button is that gesture. If the machine is muted, check the tab switch and the system switch before you blame the timer. The digits still reach zero whether the speaker is on or not. That is useful in a room that does not want noise, and it is dangerous if you were relying on a beep you cannot hear.
There is no account and nothing is uploaded. 25 minutes are not stored on a server, because there is no server on this path. Refresh the page and a running countdown is gone. For anything that must ring when a phone is locked, use the clock on the phone. This page is for a timer you are deliberately leaving on the screen: a classroom, a kitchen you are watching, or a work block you want to see tick.
The sibling pages in the same cluster are 20 minute timer and 30 minute timer. Those links stay on this site, in the language you are reading, under /ms or /zh when that is the language of the page. The path after the language stays English, including /timer/25-minute, so a link does not break between languages.