The rule
A Sudoku grid is 9×9, divided into nine 3×3 boxes. Fill every empty cell so that each row, each column, and each 3×3 box contains the digits 1 through 9 exactly once. There is no arithmetic and no guessing: a well-formed puzzle has exactly one solution reachable by logic alone.
Three techniques that solve most grids
1. Scanning
Take one digit at a time. Look at a 3×3 box and check whether that digit already appears in the rows and columns crossing it. Each appearance eliminates a whole line of cells. Often only one cell survives.
2. Last cell in a unit
When a row, column, or box has eight of its nine cells filled, the last one is forced — it must be whichever digit is missing. This site fills those cells for you the moment they become certain.
3. Naked pairs
Write candidates into empty cells using notes. If two cells in the same unit have exactly the same two candidates, those two digits are locked into those two cells — so you can erase them from every other cell in the unit.
Controls on this site
- Click or tap a cell, then press a number.
- Arrow keys (or W/A/S/D) move the selection.
- N toggles pencil-mark mode.
- H spends a hint — three per game.
- Ctrl/⌘ + Z undoes, Ctrl/⌘ + Shift + Z redoes.
- Backspace clears the selected cell.
Where to go next
Once easy grids stop being a challenge, the next step is pattern-based techniques like X-Wing and Swordfish. Our technique library covers each of them on its own page.