For the satisfying moment when two possibilities become one clear path.
A fresh daily set is ready.
Choose an empty square, then a number. You’ve got this.
Keyboard friendly 1–9 numbers N notes ⌫ erase ← ↑ ↓ → move
Classic Sudoku rules Fill every row, column and 3×3 box with the digits 1–9, using each digit exactly once. The given numbers stay fixed. Start with an empty square and check all three groups.
Our hard boards require naked pairs in addition to singles and locked candidates. Difficulty systems vary between Sudoku publishers. These boards are rated by our logical solver, so a hard label here describes the techniques needed rather than a promised solve time.
If two cells in the same row can each contain only 2 or 8, those two digits must occupy those two cells in some order. Remove 2 and 8 from the remaining cells in that row. The same principle works within a column or a box. Both cells must have exactly the same two candidates.
Keep notes tidy and inspect one group at a time. Undo lets you explore a change and return to the previous state. If you made a wrong entry, the hint system can identify a cell to review. For a valid position, hints show the reasoning behind the next logical placement.