What is Chaos Sudoku?

Chaos sudoku — also called jigsaw or irregular sudoku — uses the same rules as classic sudoku, with one difference: the nine 3×3 boxes are replaced by nine irregular regions.

The rules haven't changed

The goal is exactly what you already know. Fill the 9×9 grid so that every row, every column and every region contains the digits 1 to 9 exactly once. No digit may repeat in a row, a column, or a region.

So what's different?

In classic sudoku the nine regions are always the same tidy 3×3 boxes. In chaos sudoku each region is an irregular shape of nine connected cells. You read the regions from their colours instead of counting 3×3 boxes, and the usual box-scanning methods no longer apply, so you have to look at the grid differently.

What is Double Chaos?

Double chaos adds a second layout. The same puzzle is shown in two grids side by side, each with a completely different region layout — but both share a single solution. Every digit you place appears in both grids at once, and the answer has to satisfy both sets of regions. Because each grid gives different clues, you switch between them and use what you find in one grid in the other.

Is chaos sudoku harder?

It is different rather than simply harder. Irregular regions remove the visual shortcuts of classic sudoku, but they also allow solving techniques that do not exist in the standard game, such as the "law of leftovers". If you're new to it, our guide on how to solve jigsaw sudoku explains the main techniques.