Extreme Sudoku
Past every pattern, a wall — assume a candidate and follow it until the grid breaks.
How to play
- Fill the grid so every row, column and 3×3 box contains 1 to 9, with no repeats.
- Turn on Notes, pencil in every candidate and work the grid down as far as patterns and chains will take it.
- At the wall, pick a cell with two candidates, assume one and fill in what it forces. If the grid contradicts itself, the other one is the answer.
- Repeated numbers are highlighted gently and nothing ends the run, so erasing a line of reasoning costs nothing. The Hint covers the simple steps only.
What it trains
- The top of the ladder — every grid needs a forcing argument at least twice
- Exactly one solution in every puzzle, graded by the techniques it needs
- No account and no clock — an unfinished grid is kept on your device
Free extreme sudoku online, the hardest grids on the site: every 9×9 puzzle here reaches at least two points where the usual patterns and chains run out, and the way forward is a forcing argument — assume a candidate, follow what it forces, and when the grid contradicts itself, strike that candidate out. Every puzzle still has exactly one solution and is graded by the techniques it needs, not by how many numbers it starts with. Pencil marks are built in, the hint covers the simple steps, and there is no timer and no game over, so you can follow one line, erase it and follow another. No account and no sign-up. Plays on phone, tablet or computer.
Got thoughts on this? Tell us — it's anonymous, and every message is read.