Sudoku Technique: XY-Chain
Learn the XY-Chain Sudoku technique: how to spot and build chains of bivalue cells, why the chain can eliminate a candidate, and a clear candidate-grid example you can follow step‑by‑step.
Read articleSudoku Articles
Practical guides for solving, practicing, and understanding Sudoku puzzles.
Sudoku Technique: Unique Rectangles With Missing Candidates
How to spot and use unique rectangles with missing candidates. A practical walkthrough showing when to look, why a previously removed candidate still matters, and a clear candidate-grid example to practice on.
Read articleSudoku Technique: Empty Rectangle
Empty rectangle is a candidate-elimination pattern that uses a box-line absence to link candidates across boxes. This article explains the idea, when to hunt for it, and walks through a clear candidate-grid example you can use at the solver's table.
Read articleSudoku Technique: Jellyfish
Learn the Jellyfish sudoku technique: how to spot a four-row or four-column fish for one candidate digit, when to try it, and how to apply eliminations with a clear candidate-grid example.
Read articleSudoku Technique: Nice Loop / AIC
A clear, practical introduction to Nice Loop (also called AIC) that explains alternating strong and weak links, when to look for them, and a step‑by‑step candidate-grid example you can follow.
Read articleSudoku Technique: ALS-XZ
ALS-XZ is a practical elimination technique that uses two Almost Locked Sets (ALS) which share exactly two common candidates. Learn what an ALS is, when to hunt for ALS-XZ, a step-by-step detection method, and a clear candidate-grid example you can follow.
Read articleSudoku Technique: Remote Pair
Remote pairs use a chain of identical bivalue cells to create a strong link between the same candidate at two distant cells, letting you eliminate that candidate from any cell that sees both ends. Learn when to look for them and follow a clear candidate-grid example.
Read articleSudoku Technique: Naked Single
Learn the naked single sudoku technique: how to spot a cell that has only one possible number, when to look for it, and a clear candidate-grid example you can use while solving.
Read articleForcing Chain Sudoku Technique: Follow the Premise to a Proof
Forcing chains are a practical way to break a stuck Sudoku: assume a candidate and follow the logical consequences until you can place or eliminate a number. This article explains the idea, when to try it, and walks through a clear candidate-grid example you can practice with.
Read articleSudoku Technique: Hidden Triple
A hidden triple occurs when three digits in a row, column or box are confined to exactly three cells. Find those three cells, then remove all other candidates from them. This article explains how to spot hidden triples and gives a clear candidate-grid example you can use as a template.
Read articleSudoku Technique: XY-Wing
A clear, practical introduction to the XY-Wing sudoku technique: how to spot a pivot and two pincers in three bivalue cells and use them to eliminate a candidate. Includes a candidate-grid example you can follow step by step.
Read articleSudoku Technique: Hidden Rectangle
A clear, practical guide to the hidden rectangle sudoku technique: how it relates to Unique Rectangles, where to look, and a step-by-step candidate-grid example that shows how an extra candidate can hide the rectangle and how to eliminate it under the uniqueness assumption.
Read articleSudoku strategy topics
Use these focused guides alongside the articles when you want to practice a specific solving pattern.
Naked Singles Sudoku Strategy
A naked single is an empty cell with only one legal candidate left after checking its row, column, and box.
Hidden Singles Sudoku Strategy
A hidden single appears when a digit can only fit in one cell within a row, column, or box, even if that cell has several candidates.
Naked Pairs Sudoku Strategy
A naked pair is two cells in the same unit that contain the exact same two candidates, locking those two digits into those cells.
Pointing Pairs Sudoku Strategy
A pointing pair or triple happens when every possible location for a digit inside a box lies on the same row or column.
X-Wing Sudoku Strategy
An X-Wing locks a candidate into the same two columns across two rows, or the same two rows across two columns.
Y-Wing Sudoku Strategy
A Y-Wing uses one pivot cell and two wing cells to prove that a shared candidate cannot appear in cells that see both wings.
Swordfish Sudoku Strategy
Swordfish extends X-Wing to three rows and three columns, locking a candidate into a larger line pattern.