A pot that boils eventually — the second you stop watching it.
watchedpot simulates a single pot of water on a stove. Its progress toward boiling climbs on screen, but is mathematically capped at 99% for as long as this tab is the one you're looking at. Turn up the heat, watch the bubbles, click "check the pot" all you want — it will get close, and then it won't.
Switch to another tab, though, and the cap disappears. The moment you look away, the pot is free to actually finish boiling over — and it usually does, given enough time. When you come back, you'll either catch it right where you left it, or find out it boiled without you.
The page listens for the browser's Page Visibility API. While document.hidden is false, progress approaches its cap asymptotically — each tick closes only a fraction of the remaining gap, so it gets closer and closer without ever quite arriving, forever, like the proverb intends.
The instant the tab is hidden, the timestamp is recorded. There is no background timer secretly ticking away while you're gone — browsers throttle those anyway. Instead, the moment you return, the real elapsed wall-clock time since you left is used to calculate, after the fact, whether the pot would have boiled over during your absence. If it would have, it has. You just weren't there to see it.
The simmer is a continuous loop of filtered white noise, generated entirely by the Web Audio API — its pitch and volume rise with the heat setting. The boil-over itself is a short burst of noise swept through a bandpass filter from high to low frequency. No audio files anywhere. Note that the sound keeps playing even while the tab is in the background, so if you listen closely instead of watching, you may actually catch it happening.
Because "a watched pot never boils" is a lie you can finally verify, and because it turns out the internet had never actually tried building the pot that proves it.