Extreme puzzles get stuck where even the bigger patterns can't help. To move on you need a chain: an X-Chain that follows one digit through alternating links, or an XY-Chain through cells that can only be two numbers.
We grade every puzzle by the hardest step it needs, the way sudoku experts do: every grid on this page needs at least one chain, and every one can be solved with chains — none needs guessing. Our hints walk through each chain step by step.
Tips for extreme puzzles
Start with complete, accurate pencil marks. Auto-notes fills them in one tap.
Clear everything simpler first: singles, pairs, fish and wings. Chains are for when nothing else moves.
For XY-Chains, start from cells with two candidates and follow the forced numbers. For X-Chains, follow one digit through units where it has just two places.
Questions
How is extreme different from expert?
Expert puzzles need patterns like X-Wings and XY-Wings. Extreme puzzles get stuck even after those, and need a chain to continue.
Is every extreme sudoku solvable without guessing?
Yes. Each one has exactly one solution and is graded by a logical solve that finishes with chains, so there is always a path. The hint button names the chain and walks through it.
Can I play extreme sudoku with a friend?
Yes. "Play this with a friend" opens a multiplayer room at extreme. Two pairs of eyes help a lot with chains.
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