60
seconds
A slab swings back and forth over your tower and a word floats above it. Type the word and the swing calms down; finish it and the slab drops. Land it straight and the tower keeps its width. Land it crooked and the overhang is cut off for good.
Each new slab arrives from the side and swings over the top of the tower, first along one axis and then the other. While it swings, a word sits above it. Every correct letter pulls the swing tighter and closer to the middle. A wrong letter jolts it back outward, and if you stop typing the swing slowly widens again. The moment you type the last letter, the slab drops exactly where it is.
Any part of the slab that hangs past the edge of the floor below is sliced off and tumbles away. The next slab is only as wide as what survived, so a sloppy landing early on makes every later floor harder. If a slab misses the tower completely, or the tower gets too thin to stand on, the run is over and the camera pulls back to show what you built.
If the slab lands within a hair of the centre, it snaps into place with no cut at all and a chime plays. Each perfect in a row raises the chime a note. From the third perfect in a row, every further perfect also grows the slab back a little, so a long streak can repair an old mistake.
Under the word is a small gauge. The two marks are the edges of the tower, the green bar in the middle is the perfect window, and the dot shows where the slab is right now. A fast, clean typist usually has the swing settled by the last letter. If it is still drifting, you can hold the last key for a beat and press it as the dot crosses the middle.
Stack rewards two things that also make you faster in a normal typing test: starting a word the instant you see it, and keeping a steady rhythm without slips. Speed alone is not enough, because one wrong key undoes the calm you built up. Your accuracy and words per minute at the end are counted the same way as the main test, so you can compare them directly.
The letter does not count, the word flashes red and the slab is kicked outward. Type the right letter and the swing starts calming again. Spaces are ignored, so a habit of hitting space after a word never costs you.
A landing very close to the centre snaps exactly into place with no cut. Three perfects in a row, and every perfect after that while the streak lasts, grow the slab back a little.
The swing settles toward the centre in proportion to your pace for that word. If it is still moving when you reach the last letter, wait for the gauge dot to cross the middle before pressing it.
Yes. The tower and the word scale down to small screens and the game works with an on-screen keyboard, though a physical keyboard makes high floors much easier.