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. Standard, Advanced and Expert 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

   123456789Candidates
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. Entering the same digit again clears the cell, which is how you take a placement back on a phone.
3. 3

   Pencil in candidates

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

   Or let Auto do the pencilling

   Turn on Auto candidates(A) and every empty cell shows the digits its row, column and box haven’t ruled out — recomputed after each placement, so the marks are never stale. The real work still happens in Candidates mode: strike a digit out and it stays struck, because your strikes are kept apart from the computed set. Erase a cell to hand it back its full set, and take a wrong entry back and the candidates it was hiding return — minus the ones you had already ruled out. Your hand-written marks wait untouched behind the auto view and come back the moment you switch it off.
5. 5

   Keep your hands on the keys

   The whole board plays from the keyboard:

   ← ↑ ↓ →move between cells

   1–9enter a digit

   Backspaceerase

   Ctoggle Candidates mode

   Atoggle Auto candidates

   CtrlZundo

   Ctrl⇧Zredo