Sudoku Techniques – From Naked Singles to X-Wing
Every Sudoku technique on one page, ordered the way you actually learn them: from the two ways to place a digit, through the elimination patterns that unstick a grid, to the chains that crack expert puzzles. Each technique has its own page with a real position you can step through — not a screenshot, but a genuine grid where the pattern is provably present.
Basics
The two ways to place a digit, and the scanning habits that find them. Everything else in Sudoku exists to create these situations.
Naked Single
A cell where only one digit still fits. The most direct move in Sudoku, and the one every other technique is ultimately trying to create.
BeginnerHidden Single
A digit that fits in only one cell of a row, column or box — even though that cell looks like it has several options.
BeginnerFull House
The last empty cell in a row, column or box. One cell, one missing digit, no thinking required.
BeginnerLast Digit
When eight copies of a digit are already on the board, the ninth position is forced.
BeginnerScanning
The basic search method: follow a digit's rows and columns to see which cells it can still occupy.
BeginnerCross-Hatching
Scanning applied to a single box: rule out cells row by row and column by column until one remains.
Beginner
Subsets
Groups of cells that reserve a group of digits between them. These are the first techniques that remove candidates rather than place digits.
Naked Pair
Two cells in the same unit holding exactly the same two candidates. Those digits belong to those cells, and can be removed everywhere else in the unit.
EasyHidden Pair
Two digits that fit in only two cells of a unit. Everything else in those cells can be discarded.
EasyNaked Triple
Three cells in a unit that between them use only three candidates. Those three digits are reserved for those cells.
EasyHidden Triple
Three digits confined to the same three cells of a unit, no matter what else those cells show.
AdvancedNaked Quad
Four cells in a unit using only four candidates between them. Those digits are locked into those cells.
AdvancedHidden Quad
Four digits restricted to the same four cells, letting you clear everything else from them.
Hard
Intersections
Where a box meets a line, information flows both ways. The best value for the effort on medium and hard puzzles.
Fish patterns
Single-digit patterns spanning several rows and columns, from the classic X-Wing to its larger and asymmetric relatives.
X-Wing
A digit forming a rectangle across two rows and two columns. One of the two orientations must be correct, which eliminates the digit elsewhere on those lines.
AdvancedSwordfish
The three-line version of the X-Wing: a digit confined to three rows and three columns.
HardJellyfish
The four-line fish. A digit restricted to four rows and four columns clears those columns everywhere else.
ExpertSkyscraper
Two lines sharing a base but with tops in different columns. Cells seeing both tops can drop the digit.
AdvancedTwo-String Kite
A row and a column, each with two candidates, meeting through a shared box. Their far ends cannot both be false.
AdvancedEmpty Rectangle
A box where a digit's candidates form a cross rather than a rectangle, combined with a strong link elsewhere.
Hard
Wings
Short forcing arguments across three or four cells and several digits. Where real logic begins.
XY-Wing
Three bi-value cells forming a hinge and two wings. Cells seeing both wings cannot hold the shared digit.
AdvancedXYZ-Wing
Like an XY-Wing, but the hinge carries three candidates. The eliminations are fewer but the pattern is more common.
HardW-Wing
Two identical bi-value cells connected by a strong link on one of their digits.
Hard
Chains and uniqueness
Longer arguments and techniques that use the puzzle's uniqueness. The tools for expert-level grids.
Simple Colouring
Follow one digit's strong links across the board with two alternating colours, then look for contradictions.
HardRemote Pair
A chain of cells all holding the same two candidates. The ends behave like a pair even when far apart.
HardUnique Rectangle
A pattern that would create two solutions. Since a proper puzzle has only one, it can be ruled out.
HardBUG+1
When every unsolved cell but one has two candidates, the odd cell out must take its third digit.
ExpertForcing Chain
Assume a candidate, follow the consequences, and see whether both assumptions lead to the same result.
Expert