How to play Sudoku

A standard grid has nine rows, nine columns, and nine bold 3×3 boxes. The printed digits are givens and cannot be changed. Your entries must complete all three kinds of region at the same time, so a number that looks possible in a row may still be blocked by its column or box.

The digits are symbols rather than quantities. A row does not need to add to a total, and consecutive numbers do not have to touch. The only test is whether each digit from 1 to 9 appears once in every row, column, and box.

Begin with crowded rows, columns, and boxes because they have fewer missing digits. Suppose a row is missing 2 and 7. If the empty cell in one column already sees a 7, that cell must be 2; the other empty cell is then 7. This is a naked single: the cell itself has one candidate.

Also scan one digit at a time. Pick a box and ask where its 6 can go. Existing 6s in crossing rows and columns may block every square except one. That is a hidden single: several candidates may fit the cell, but only one cell in the region can take that digit.

Candidate notes record the digits that remain legal in a cell. They are most useful when the grid no longer offers obvious singles. Keep them accurate: whenever you place a digit, remove it from peer cells in the same row, column, and box.

Do not treat a short candidate list as permission to choose. A cell containing 3 and 8 is unresolved until another constraint removes one option. Compare repeated candidate patterns across a region instead. Two cells containing the same pair, for example, can reserve those digits and eliminate them from other cells in that region.

The most common error is checking only two constraints. Before placing a digit, verify the row, column, and box. A second error is guessing when progress slows. A guess may appear to work for many moves before creating a contradiction, making the real mistake difficult to locate.

Another trap is scanning the whole grid without a question. Use a repeatable loop: inspect crowded regions, look for a specific missing digit, update notes, then rescan the regions changed by your last placement. A focused loop is both faster and easier to audit.

Start with an easy puzzle and explain each placement to yourself in one sentence. If you cannot name the row, column, box, or candidate pattern that proves the move, pause instead of entering it. Accuracy builds speed more reliably than racing the timer.

When stuck, request an explanatory hint rather than a filled answer. Then find the highlighted evidence on the board before continuing. Clever Pause saves progress locally, so you can leave a difficult grid and return with fresh eyes without creating an account.