Sudoku

🎯 Objective

Fill all 81 squares so the digits 1 to 9 appear exactly once in every row, every column and every 3x3 box. There is only ever one solution, and it can always be reasoned out.

📊 How you score

Your score is points, and higher is better. Every day has its own points ceiling that rises with the difficulty, so a Sunday grid is worth four times a Monday one and a fast Monday can never top the all-time board. Solve inside the day's grace period and you keep the whole ceiling; take longer and it decays gently from there. Boo can point out the next forced move up to 3 times a grid, and each hint costs a slice of that day's ceiling, so it is a real trade rather than a free answer. Slips cost a little too, capped so a wobbly patch never sinks a run. Solving on consecutive days builds your solve streak.

💡 Tips

• Scan for the digit that is already placed most often. The more copies on the board, the fewer squares are left for the next one.
• Work a box, a row and a column that all cross the same empty square. A digit ruled out by any one of them is ruled out for good.
• From Thursday on, pencil marks stop being optional. A square with only two candidates is the thread to pull.
• Two squares in a unit holding the same two candidates lock those digits away from every other square in that unit.
• Stuck? Tap Boo above the board. Three hints per grid, and each one names the rule that proves the move, so you learn the pattern rather than just the answer.