Sudoku

Preparing the board…

Rules and controls

Fill each row, column and 3×3 box with the digits 1–9, each exactly once. Given numbers cannot be changed. Select an empty cell and use the keypad or type a number; arrow keys move between cells. Notes record candidates; Erase clears a value or notes. Conflicts are marked when a digit repeats in a row, column or box.

For example, if a row already contains 1, 2, 3, 4, 5, 6, 7 and 8, its empty cell must be 9 — and 9 must also fit that cell’s column and 3×3 box. Notes are pencil marks for possible answers, not answers in the grid; switch Notes on before entering one, and entering a value clears that cell’s notes. A conflict marker only means a digit repeats in a row, column or box; a wrong answer can still be wrong without creating a duplicate.

Reveal cell provides the answer for your selected cell and marks this attempt assisted. Undo reverses edits. Easy starts with extra given numbers and uses singles; Medium adds locked candidates or naked pairs; Hard requires hidden pairs or X-Wing without guessing. Every puzzle is checked for exactly one solution.

A Daily Sudoku link is dated and saves in its own slot. New game on that link opens the ordinary Sudoku page; there, New game picks a fresh random puzzle while Restart keeps the same deal.