Place stars so that every row, every column and every region holds the same number of them, and no two stars ever touch — not even corner to corner. The regions are irregular shapes, which is where the difficulty lives.

• 2,004grids produced and checked
• 12solving techniques, in five levels
• 364daily challenges, a year per weekday

Five shapes of puzzle

From 8×8 with one star per region up to 14×14 with three. The largest are the hardest to make: a single 14×14 grid at the top level takes about six and a half minutes of computation, and two tries in five are abandoned.

One solution, proved by a second opinion

Every grid is passed to a SAT solver that shares no reasoning with the logic solver and counts the solutions. A grid with two never enters the bank. The stored answer is then checked against the one the SAT solver found, and the difficulty is recomputed from scratch.

The level is earned, not assigned

A grid's level is the hardest of the twelve techniques the solver had to use, easiest first. The top level never appears on its own — it has to be forced, and only the larger multi-star shapes can reach it at all.

No technique that leans on the answer

The solver never argues that the puzzle has one solution, therefore this. Two of the twelve do test an idea in order to refute it, which is a different thing from keeping a guess.

There is no app. Not a line of Swift, no project, no icon. What exists is the content and the machinery that grades it: 2,004 verified grids, a solver that does not guess, and a year of daily challenges ready for the day the game is built.