Sudoku

The classic logic puzzle: fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1–9 exactly once. No guessing is ever needed — a proper sudoku always has one solution you can reason your way to. Easy, Intermediate and Hard boards arrive daily at midnight UTC, each with its own clock and daily best.

1. 1

   Read the board

   Printed digits are the givens — they never move. Your own entries appear in blue, and a wrong digit turns red the moment you place it. Mistakes cost time, not lives, so an experiment is never fatal.

   5Given

   3Yours

   7Wrong

   123456789Notes
2. 2

   Select and fill

   Click a cell and type a digit. To work faster, drag across several cells — or Shift/Ctrl-click to build up a selection — and one keystroke fills them all. Handy when a digit’s remaining homes are all decided at once.
3. 3

   Pencil in notes

   Switch to Notes mode (or hold the thought and press N) to jot candidate digits into empty cells, just like pencil marks on paper. Place a correct digit and it sweeps itself out of the notes in its row, column and box.
4. 4

   Keep your hands on the keys

   The whole board plays from the keyboard:

   ← ↑ ↓ →move between cells

   1–9enter a digit

   Backspaceerase

   Ntoggle Notes mode

   CtrlZundo