Sudoku techniques
Every technique Sudoku Sova grades its puzzles by, from the first single to the XY-chain — each with a worked example from a real puzzle.
Levels are graded by technique. No puzzle ever needs a guess.
Fast
Easy
Medium
Naked pairTwo cells share the same two options, so those numbers are locked out of the rest of the group.
Pointing pairInside this box the number sits on a single line, so it can leave that line elsewhere.
Pointing tripleInside this box the number sits on a single line, so it can leave that line elsewhere.
Box-line reductionAlong this line the number sits in a single box, so it can leave that box elsewhere.
Hard
Naked tripleThree cells share the same three options — clear those numbers from the rest of the group.
Hidden pairTwo numbers fit in only these two cells, so nothing else can go there.
Hidden tripleThree numbers are confined to these three cells — remove every other option from them.
Expert
X-WingThis number forms a rectangle, which rules it out along two lines.
XY-WingThree linked cells force this number out of any cell two of them both see.
SkyscraperTwo lines hold the number in only two places each and share one of them — so anything seeing both far ends is ruled out.
W-WingTwo cells with the same two options are linked by a third line, so any cell seeing both loses the other option.
Fiendish
SwordfishThe number is confined to three lines that touch only three crossing lines, which clears it everywhere else along them.
ColouringFollow the number's two-place chains, alternating as you go: one colour must be false, and anything seeing both colours is ruled out.
XYZ-WingOne of these three cells must hold this number, so nothing seeing all three can.
Master
JellyfishThe same number is boxed into four lines, so it can leave those columns elsewhere.
Remote pairsA chain of the same two numbers alternates, so the ends differ — clear both from anything seeing both ends.
Empty rectangleInside this box the number sits on one row and one column; pair that with a two-spot line to clear the crossing.
Extreme
Two-string kiteThe number has two places in a row and two in a column, and one of each shares a box — so anything seeing both far ends is out.
Finned X-WingAn X-Wing with a spare place or two in one box: either the X-Wing holds or the number is in that box, and the cells that see both lose it.
Unique rectangleThree corners of a rectangle carry the same two numbers; the fourth can take neither, or the puzzle would have two answers.
BUG+1With every cell down to two candidates a grid would have two answers — so the one cell left with three takes the number that appears three times in a unit.
XY-chainA run of two-candidate cells that starts and ends on the same number: one end must be it, so anything seeing both ends is out.
In the app, Sova teaches the technique behind every move: a hint shows where to look, then names the technique, then shows it. No account, no ads during a puzzle.
Get Sudoku Sova