Sudoku Basics

Sudoku is a logic puzzle that fits inside a 9×9 grid, divided into nine 3×3 boxes. The rule is simple: every row, every column, and every 3×3 box must contain the numbers 1 through 9, with no repeats. The puzzle starts with some cells already filled in — these are the givens — and your job is to deduce the rest using only logic. That single rule produces an enormous amount of structure. Once you know there is already a 1 in a row, you know the 1 in that row's three boxes must sit in one of the remaining cells. Once you spot a 3×3 box that already has eight numbers, you can fill the last one without thinking. The whole puzzle is solvable from the rule plus careful reading — no math beyond the digits 1 through 9, no guessing if the puzzle is well-formed. If you've never solved a sudoku before, the most useful first skill is systematic scanning. Pick a digit — say, 5. Look at each 3×3 box in turn and ask: where could the 5 go? If the row above, the column beside, and the existing fives in nearby boxes leave only one cell, you've found a placement. Repeat for the next digit. After a few passes through all nine digits, easy puzzles start solving themselves. When scanning runs out of new placements, the next step is to track candidates — the numbers that could still go in each cell — either mentally or by writing small pencil marks. Candidate tracking is what separates a casual solver from a consistent one, and it's the foundation for every advanced technique covered in our Strategies section. The articles in this category cover the rules in full, the vocabulary used by experienced solvers (givens, units, candidates, scanning), and the path from your first complete grid to confidently tackling medium and hard puzzles. Start with the rules guide, work through a few easy puzzles on our /play page, then come back here when you're ready for the next step.