How to enter a puzzle
Tap a square and type a digit (or use the buttons under the grid). Arrow keys move around; Backspace clears. Or paste a whole puzzle as 81 characters, row by row, with 0 or a full stop for blanks. The famous example already loaded is the puzzle from the Wikipedia Sudoku article.
Stuck, not lost
Most people don't want the whole answer. They want the one cell they missed. Next step gives you exactly that, names the technique, and highlights the cells that prove it. Turn on candidates to see the pencil marks the solver is working from; eliminated candidates are struck through in red.
The techniques it uses are explained with worked examples on the Sudoku strategy page.
Ask the puzzle coach
Stuck on a rule or a tactic? Ask in plain words. The coach only talks puzzles, and the answer is written for you on the spot.
Questions players ask
How does the Sudoku solver work?
Next step looks for the simplest human technique that makes progress (naked single, hidden single, naked pair, pointing pair) and explains it. Solve all uses a fast backtracking search that also counts solutions, so it can tell you if a puzzle is broken or has more than one answer.
Can it solve any Sudoku?
Any valid 9×9 Sudoku, including the hardest published ones, in well under a second. If the digits you typed contradict each other it tells you so instead.
Why does Next step sometimes say "checked by trial"?
Very hard puzzles need techniques beyond pairs (X-wings, chains). When none of the included techniques applies, the solver reveals one cell from the unique solution so you can keep going.
Is my puzzle sent anywhere?
No. Solving happens entirely in your browser.