I built a daily puzzle where a piece of paper is folded and hole-punched, and you predict where all the holes end up when it's unfolded. It's the kind of thing I used to do in grade school with actual paper and scissors, and it turns out the mental version is a surprisingly good spatial reasoning challenge.

Three difficulties each day: easy is a 4×4 grid with one fold, hard is 6×6 with three folds.

It's built with Next.js. The puzzles are generated deterministically on the fly using a daily seed.

The engine runs a forward simulation of the paper folds using 2D coordinate mirroring, then calculates a "cognitive difficulty score." It weights factors that mess with human spatial reasoning, like off-center folds that break obvious symmetry and mixed-axis folding. It then automatically rerolls the daily seed until the easy, medium and hard puzzles form a good difficulty curve.

Would love to hear your feedback!