Diag (Mind Loft)

Diag adds one rule to classic sudoku: the two long diagonals, corner to corner, are extra houses that must each hold 1 through 9 exactly once. Rows, columns and 3x3 boxes still follow the normal rules. The diagonals are tinted and ruled across the grid, and selecting a square on one highlights the whole diagonal along with its row, column and box.

A diagonal works like any other house, so it can give you a hidden single, and the centre square, which sits on both diagonals, sees more of the board than any other. Mind Loft builds every board so the diagonals are needed: read as an ordinary sudoku, the same printed digits would allow more than one solution. Every grid still has a single solution reachable by logic. Wrong entries are not flagged, and a clean solve scores a perfect 10, with the leaderboard decided on time.

The number of printed digits falls through the week, from 26 on Monday to 16 on Saturday, and the Sunday Edition prints only fourteen. Notes, Undo, Erase, Clear, auto-move and a hint are all available. A new board arrives every day at midnight Eastern, and past boards stay in the archive. Mind Loft runs a whole row of daily sudoku variants beside it, among them Suds (classic), Knight (anti-knight), Cages (killer), Frame and Polka.