Goal: Fill the 9×9 grid so each row, column, and 3×3 box contains digits 1-9. Red numbers show errors.
Controls: Click cells and use number buttons or keyboard (1-9). For faster entry: select a number button first and enter into the proper location, then double-click on cells to quickly place that number. Press 'N' for notes mode, 'H' for hints, 'U' for undo. Ask for a hint if it looks like there isn't a unique solution (the master puzzles are not all perfect!).