Stuck? Turn on Notes and pencil in every candidate — the singles reveal themselves.
Sudoku — free online sudoku puzzles in your browser
Sudoku is the world's favorite logic puzzle: place the digits 1–9 so that each row, each column and each 3×3 box contains every digit exactly once. This version generates a fresh puzzle every game — each one checked by a solver to guarantee exactly one solution, so pure logic always gets you home, never guessing. Pencil notes, error highlighting and a timer are built in.
Play free with no download or sign-up, on your phone or computer. Your fastest time for each difficulty and your lifetime solve count are saved on your device.
How to play
- Tap a cell, then tap a number on the pad (or press 1–9 on a keyboard; arrow keys move the selection).
- Bold digits are givens — they can't be changed. Yellow digits are yours.
- Toggle ✏️ Notes to pencil small candidate digits into empty cells; ⌫ Erase clears a cell.
- With ⚠️ Errors on, any digit that clashes with its row, column or box turns red.
- Complete a row, column or box correctly for a satisfying flash — fill the whole grid to win and set a best time.
Sudoku strategy: from scanning to pencil marks
Every sudoku yields to the same ladder of techniques. Start by scanning: pick a digit that already appears often and cross-hatch the rows and columns it occupies — in many boxes only one cell remains for it (a hidden single). Next look for naked singles: cells whose row, column and box together already contain eight digits, leaving just one choice. Easy puzzles fall entirely to these two moves.
When singles dry up, switch to pencil marks. Note every candidate in the empty cells of one unit, then hunt for pairs: if two cells in a row share exactly the candidates 4 and 7, no other cell in that row can hold 4 or 7 — eliminate them and new singles appear. Harder puzzles chain these eliminations (locked candidates, box-line reduction), but the discipline matters more than the jargon: update your notes after every placement, and never write a digit you can't justify. Because this generator guarantees a unique solution, a logical path always exists — if you're stuck, the puzzle isn't broken; a single is hiding in plain sight.
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