Flip a Coin — a fair 50/50 heads or tails online

It's a time-management method: focus on a single task for 25 minutes, rest for 5, repeat that four times, then take a longer 15–30 minute break. Francesco Cirillo started it in Italy in the late 1980s with a tomato-shaped kitchen timer, hence the name "pomodoro", Italian for tomato. If 25 minutes feels long, shorten it in the settings; for deep work you can stretch it to 50 minutes of focus and 10 of rest. Pomodoro Technique® is a registered trademark of Francesco Cirillo.

Yes. Browsers wake timers in hidden tabs only once a second or even once a minute, so a timer that subtracts one every second drifts by minutes. This one fixes the end time when you press start and compares it with the current time on every update, so the remaining time is right even if it wakes late, and with auto-start on, the next round is counted from the moment the previous one actually ended. On a phone, though, turning the screen off or switching apps can pause the page itself, so the sound may come late. In that case, turn on "Keep screen on".

Browsers don't let a page make sound until you've clicked on it once. Sound works from the moment you press Start, and you can check the volume with "Preview" in the settings. For notifications, turn on "Notify me when a round ends" and allow the permission the browser asks for; if you blocked it before, allow notifications again in the site settings to the left of the address bar. Safari on iPhone and iPad only sends web notifications from sites added to the Home Screen.

Only in this browser (localStorage); nothing is sent to a server. It keeps the number of sessions and minutes per day for the last 90 days and isn't shared with other devices or browsers. It disappears when you press "Clear history" or clear the browser's site data. Your task note and the coin and dice history are kept in the same place.

Yes. It uses the browser's built-in cryptographic random number generator (crypto.getRandomValues) to pick heads or tails with exactly 1/2 each. Interestingly, real coins aren't quite 50/50. In 2007 Diaconis and colleagues at Stanford found that a hand-flipped coin lands on the side that was facing up before the toss about 51% of the time, and in a 2023 experiment where 48 people flipped coins 350,757 times, the starting side came up 50.8% of the time. It happens because a spinning coin wobbles around its axis.

No. Flip a fair coin 20 times and there's about a 77% chance of a run of four or more of the same side, and about 46% for five or more. People feel that an even mix of heads and tails looks "random", but real randomness produces streaks more often than we expect. Five heads in a row don't make tails more likely next time, either — every flip is exactly 50/50.

Read it as "number d sides". 2d6 is the sum of two six-sided dice, d20 is one twenty-sided die and d100 (d%) gives 1 to 100. Adding +3 or -2 adds to or subtracts from the total, and you can mix kinds, as in 3d6+1d4. kh3 keeps the highest three, kl1 keeps the lowest one and dl1 drops the lowest one. So 4d6kh3 is the D&D ability score roll, 2d20kh1 is advantage and 2d20kl1 is disadvantage. You can roll up to 100 dice at once, with up to 1,000 sides.

For the roll you just made: the chance of getting exactly that total, the chance of that total or higher, and the average. They're exact, worked out by counting every combination rather than estimated from samples. For example, 7 is the most common total on 2d6 at 6/36 ≈ 16.7%, while 12 is 1/36 ≈ 2.8%. If there are so many dice or sides that the combinations get out of hand, it skips the odds and shows only the possible range.

Yes. After a roll, tap the dice you want to keep; they're held with a lock mark, and the next roll leaves them alone and re-rolls only the rest. It's handy for Yacht-style games where you collect the faces you want from five dice. To release a die, tap it again or press "Release all". Changing the notation releases all dice.