Sudoku guides

Written explanations of the techniques that actually solve puzzles, in roughly the order worth learning them. Every diagram is a real position taken from a generated puzzle, and every deduction shown is verified against the puzzle’s unique solution before it ships.

If you would rather be shown a move on your own board than read about one, the game explains the next step on whatever position you are looking at.

• How to solve Sudoku: a beginner’s guideLearn Sudoku from scratch: the one rule that matters, how to scan a grid, the first two techniques that solve most easy puzzles, and what to do when you get stuck.8 min read
• Naked singles and hidden singles explainedThe two techniques that finish most Sudoku puzzles, and the difference between them. Worked grids for each, plus why hidden singles are so much harder to spot.7 min read
• Sudoku pencil marks: how to use notation properlyWhen to start marking candidates, how much to write down, and how to keep marks from going stale. The habit that separates people who finish hard puzzles from those who stall.7 min read
• Naked pairs, triples and quads in SudokuHow locked sets work: two cells sharing two candidates, three sharing three, and why the counting argument behind them is the same every time. With verified grids.7 min read
• Hidden pairs and hidden triples in SudokuHidden subsets are the mirror image of naked ones, and often easier to spot once you know to count digits instead of comparing cells. Worked example on a real grid.6 min read
• Pointing pairs and box/line reductionLocked candidates in both directions: when a digit in a box is stuck on one line, and when a digit on a line is stuck in one box. Both shown on the same grid.7 min read
• The X-wing technique in Sudoku, explainedThe first advanced Sudoku pattern worth learning: what an X-wing is, the argument that makes it work, how to find one, and when it is a waste of time to look.8 min read
• How to solve Sudoku fasterSpeed in Sudoku comes from search order, not from thinking quicker. A concrete scanning routine, what to do when stuck, and the habits that waste the most time.7 min read
• Nine common Sudoku mistakes, and how to stop making themGuessing, stale pencil marks, checking only one line, restarting instead of debugging. The specific errors that cost solvers the most time, and the fix for each.8 min read
• What actually makes a Sudoku puzzle hard?Clue count is a bad measure of difficulty, and here is why. How puzzles are really graded, why 17 clues is the minimum, and what “unique solution” guarantees.7 min read