Pick a piece (or press its key) and a tool. The brush paints as you drag, Fill paints an area, Rectangle and Outline a box, and Copy lifts a region to paste (and flip or turn). The right button clears. Play tests the level with the arrows and Space, and Esc stops. Winning it records a solution that the link and the .SP file carry. Edits keep the solution while it still wins, and when one breaks it, the page says when and marks the cell.