Evil Sudoku
Every grid has a knot that only a chain of linked pencil marks will untie.
How to play
- Fill the grid so every row, column and 3×3 box contains 1 to 9, with no repeats.
- Turn on Notes and pencil in every candidate — the chains that crack these grids run through your pencil marks.
- When the simple moves run out, trace a candidate: if it were true, what else would have to be? Where two threads of that reasoning meet, a candidate falls.
- Repeated numbers are highlighted gently and nothing ends the run, so you can erase a thread and try another. The Hint covers the simple steps only.
What it trains
- Chains, not scanning — every grid stops at least twice where only linked pencil marks move it on
- 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 evil sudoku online, for players who have run out of road on expert: every 9×9 grid here stops at least twice where the simpler techniques will not move it, and the way through is a chain — coloring one candidate across the grid, or following an X-chain, XY-chain or alternating inference chain until a candidate has to fall. Every puzzle 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 a grid can stay open until the chain shows itself. No account and no sign-up. Plays on phone, tablet or computer.
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