Classic Sudoku
Fill a 9x9 grid so every row, column and 3x3 box holds the digits 1 to 9 once. The classic puzzle and the best place to start.
This wiki explains the rules of every Sudoku69 game, the techniques that solve them and the guides that tie it together. It helps beginners learn a first puzzle and experienced players reach the harder levels, in all six difficulty levels of every mode.
Fill a 9x9 grid so every row, column and 3x3 box holds the digits 1 to 9 once. The classic puzzle and the best place to start.
A 9x9 grid split into cages with target sums. No digit repeats inside a cage, and harder levels give no starting digits at all.
A bigger grid with 16 symbols (1 to 9 and A to G) and 4x4 boxes. Same logic as classic, but each solve takes much longer.
Solving techniques form a ladder, from simple singles up to forcing nets. There are 37 in total, and learning them in order works best. Each article has a worked example and matches a difficulty level, so the full solving techniques list shows what to learn next.
Learn how to play Sudoku: the three rules, how the 9x9 grid works, a worked first move, pencil marks and how to start as a beginner.
Learn how to solve a sudoku puzzle with a repeatable method: scan for singles, add pencil marks, use pairs. Includes a real puzzle solved move by move.
Sudoku tips and strategies for beginners: scan the grid, use crosshatching and pencil marks, check as you go, and never guess. Includes a worked Easy example.
How sudoku difficulty is rated: six levels from Easy to Legendary, what each one needs, why clue count misleads and how to pick the level that suits you.
Killer sudoku rules explained: cages, sums, no repeats, and how it differs from classic sudoku. Learn the 45 rule and your first moves, then play online.
Killer Sudoku combinations chart for cages of 2 to 9 cells: every digit set for every sum, with single-combination sums marked. Use it as a cheat sheet.
Innies and outies use the 45 rule to read a digit straight off a Killer Sudoku cage layout, before you write a single candidate.
Killer Sudoku cage combinations show which sums have only one possible digit set. Learn the forced sums and lock digits in on your first pass.
Learn about Killer Sudoku and other math-based Sudoku variants that combine logic with arithmetic.
Naked and hidden singles are the two ways a Sudoku forces a digit into a cell. Learn to spot both and finish easy grids without guessing.
Naked and hidden pairs lock two digits into two cells. Learn to spot both patterns and clear the candidates that block your next single.
Pointing pairs lock a digit into one row or column inside a box, clearing it from the rest of that line. Learn to spot and use the pattern.
The X-Wing Sudoku technique explained: how one digit locked into two columns across two rows lets you delete it everywhere else in those columns.
The Y-Wing Sudoku technique explained: how a pivot cell and two pincers with three shared digits force an elimination in every cell that sees both pincers.
Explore different types of Sudoku puzzles including Killer Sudoku, Giant Sudoku, and constraint variants.
Who invented Sudoku and what the name means: Howard Garns, Dell Number Place in 1979, Nikoli in 1984 and The Times in 2004, with a timeline.
How many sudoku grids exist, why 17 clues is the minimum, whether every puzzle has one solution, and whether sudoku is maths. Numbers, sources and our own data.
What makes a sudoku the hardest: rating, not clue count. Our hardest home puzzles (killer 12.8, classic 11.1, 16x16 10.4) and how to attack a Legendary grid.
Does sudoku help your brain? What studies on number puzzles, memory and dementia risk found, where the evidence is weak, and how to get the most from playing.