Choose Your Challenge
10 classic difficulty levels — plus an Advanced Lab for power solvers
Reading Candidates
Learn pencil marks — the notation every technique above Level 2 depends on.
FoundationsLevels 1–4
Singles & Pairs
Naked Single
Only one candidate remains in a cell
Hidden Single
Only one cell in a row/column/box can contain a candidate
Naked Pair
Two cells in a unit share the same two candidates
Hidden Pair
Two candidates appear only in two cells within a unit
IntermediateLevels 5–10
Fish & Wings
Pointing Pair
A candidate in a box appears only in one row/column within that box
Box-Line Reduction
A candidate in a row/column appears only in one box
X-Wing
A candidate appears in exactly two rows and two columns forming a rectangle
Swordfish
X-Wing expanded to three rows and three columns
XY-Wing
Three cells with candidates forming elimination patterns
XYZ-Wing
Variation where the pivot cell contains all three candidates
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Beyond Classic Sudoku
Skyscrapers, kites, colors, AICs, ALSs and forcing chains — quirky, rare techniques that don't show up in NYT-style puzzles. Open the Lab if you're hunting them.
Unlock Levels 5–10 + the Advanced Lab
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