Arrow

Arrow is one of the sudoku variants on Mind Loft, a free puzzle site played in the browser with no app and no account needed. The grid follows the usual sudoku rules: every row, column and 3x3 box holds the digits 1 to 9 once each. On top of that, arrows are drawn across the grid. Each arrow starts in a circle and runs through a short line of squares, and the digit in the circle is the sum of the digits on its line.

A new board arrives every day at midnight Eastern time and is the same for everyone. The week has a shape: Monday's board prints 28 digits and each day prints fewer, down to 13 on Saturday, while the Sunday Edition gives just eight printed digits under twelve arrows, so most of the work is done by the sums.

The deductions are mostly about combinations. A circle of 3 on a two-square arrow can only hold 1 and 2, and a big circle on a long arrow forces small digits along it. A digit may repeat along one arrow only where the two squares share no row, column or box. Mind Loft says every board has a single solution reached by logic alone.

Wrong entries are not flagged while you play, so checking your own work is part of the puzzle. A clean solve scores a perfect 10, and the daily leaderboard is ranked by time. There are notes for pencil marks, a hint button, and an archive of past boards. Arrow suits sudoku players who know the classic grid and want arithmetic in the logic; Mind Loft's Cages (killer), Sando (sandwich) and Mercury (thermo) are its sibling variants.