Fourfold Observatory
Fill rows, columns and 2×2 boxes with 1–4. This diagonal variant also requires both long diagonals to contain 1–4. Select a cell then digit; Check validates.
How to play & source
Fill rows, columns and 2×2 boxes with 1–4. This diagonal variant also requires both long diagonals to contain 1–4. Select a cell then digit; Check validates.
Touch the tiles and controls. Keyboard: Tab, Enter or Space activate any button; arrows move in movement games. R restarts; Z undoes calm puzzles. Cell numbers are shown in each tile’s upper-left corner.
Mechanic research: Ultimate Sudoku CollectionOriginal small-board interpretation, not an official port. Original code, names, layouts and CSS-drawn tiles. No external assets, trackers or network requests.
New tactical layer
The Starlight lens computes candidates from row, column, box and both diagonal peers. It inks only a forced singleton and otherwise shows the remaining possibilities.