Sudoku Guides

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How to solve a sudoku: a step-by-step beginner walkthrough

One real easy puzzle, solved in front of you, with the reason for every digit and grids showing the progress.

Hidden singles and naked singles

The two ideas behind almost every digit you place, each worked through on a real puzzle, plus a routine for spotting them.

Pencil marks: how to take notes without drowning in them

When to start writing candidates, full versus partial marking, how our game's notes work, and how notes reveal patterns like pairs.

Common sudoku mistakes and how to get unstuck

The habits that stall most solvers, how to catch a wrong digit before it spreads, and a step-by-step routine for when you're stuck.

Techniques for hard puzzles

Locked candidates: pointing and claiming

The first technique that removes candidates instead of placing digits, with real examples of pointing and claiming.

Naked and hidden pairs, triples and quads

Squares that share digits so tightly the rest of the unit loses them, with worked naked and hidden pairs and triples.

Techniques for expert puzzles

X-Wing: how to find it and why it works

The rectangle pattern that clears a digit from two whole lines, with a real example and a step-by-step check of why it holds.

Swordfish and Jellyfish

The X-wing stretched to three and four lines, with a real swordfish, a rare real jellyfish, and how often each was needed.

XY-Wing and XYZ-Wing

Three two-candidate squares that together rule out a digit, plus the XYZ-wing variant, each on a real puzzle position.

Killer sudoku

Killer sudoku cage combinations

Every possible set of digits for every cage size and total, with the digits each total always and never uses.

Killer sudoku strategies: the 45 rule, innies and outies

The rule of 45, innies and outies worked through on a real grid, and how cages in the same row or box limit each other's digits.

Behind the puzzles

How sudoku puzzles are made, and why one solution matters

How our generator builds a full grid, removes digits while the answer stays unique, and grades each puzzle by the techniques a person would need.

For a one-page summary of every technique, see the techniques page. New to the game? Start with how to play.