Classic Sudoku

Each row, column and 3 × 3 box contains the digits 1–9 exactly once.

1. Select an empty cell, then choose a digit or switch Notes on.
2. Ask for a gentle hint: attention first, proof next, then the conclusion only when you request it.
3. Undo uncertain moves or pause. Every puzzle is open; daily selections use a separate save.

Select a cell · 1–9 fill · N notes · arrows move · Delete erase · Ctrl/Cmd Z undo

A note records an option, not a commitment. If a cell sees 1, 2, 4, 5, 6, 7, 8 and 9 in its row, column or box, its only candidate is 3. Read all three units before filling it.

For a hidden single, scan a whole unit for one digit. Several cells may have multiple notes, yet only one cell can hold that digit. Notes are manual; the optional candidate tool changes notes as one reversible action.

Try a pair only when exactly two cells in the same unit contain the same two options. Remove those options from other cells in that unit. An uncertain digit without a rule conflict is not automatically marked wrong.

Game progress belongs to this browser and this address. Use the game’s own save tools where available. Changing addresses or clearing browser data does not transfer your save.