Sudoku
Tap a cell and pick a number so every row, column and box holds 1 to 9 once; pencil in notes, and wrong entries turn red.
Built with
How it was made
Written with Claude Code as a single web page with no libraries; each puzzle is generated on the spot by filling a random grid, then removing cells in pairs and re-counting the solutions after every removal, putting a cell back whenever a second solution appears.