How to Use Notes (Pencil Marks) in Sudoku
Notes record which digits can still go in each empty cell. When to start taking them, how to keep them accurate, and how to read them for answers.
Sudoku Blog
Techniques explained one at a time, each with a lesson you can practice in the Technique Journey.
How to Play Sudoku: Rules and Your First Solve
The rules of sudoku in one sentence, the words you need to know, and a simple method to finish your first puzzle. No math required.
Naked Singles and Hidden Singles, Step by Step
The two techniques that solve most easy and medium sudokus. What each one is, how to spot it fast, and where to practice.
Pointing Pairs and Box/Line Reduction, Explained
Two intersection techniques that unlock most Medium puzzles: what pointing pairs and box/line reduction are, how to tell them apart, and how to spot them.
Naked Pairs, Triples and Quads Explained
When two cells share the same two candidates, those digits are taken. How naked pairs, triples and quads work, and how to spot them.
Hidden Pairs and Triples in Sudoku
When two digits can only go in the same two cells, everything else in those cells can go. How hidden pairs and triples work and how to find them.
X-Wing: The First Advanced Sudoku Technique Worth Learning
When a digit fits in the same two columns of two rows, you can clear it from the rest of both columns. How x-wings work and how to spot them.
Swordfish in Sudoku, Explained
A swordfish is an x-wing with three rows and three columns. How the pattern works, why each row doesn't need all three columns, and how to find one.
What Makes a Sudoku Hard? How Difficulty Is Rated
Sudoku difficulty comes from the techniques a puzzle forces you to use, not how empty it looks. The technique ladder, givens, and how to get better.