Killer Sudoku (BrainBashers)

Killer Sudoku on BrainBashers keeps the classic sudoku rules (every row, column and 3x3 block holds 1 to 9) and adds cages. Each cage is outlined with a dotted line and shaded in a colour, and the small number in its corner is the total its digits must reach. A digit may not repeat inside a cage. The page points out that this differs from CalcuDoku, the site's other cage puzzle, where numbers can repeat in a cage and other operations are used.

Every day brings four puzzles graded Easy, Easy/Medium, Medium and Medium/Hard. Each opens on its own dated page made by Kevin Stone, with check, pencil marks, undo, answer, print and restart buttons, options to show mistakes or duplicates, and an on-screen clock if you want one. A help page explains the method, and a separate page lists the possible digit combinations for each cage total and size, which is the main tool for this kind of puzzle.

The puzzles change at midnight GMT, or at the time zone you set, and a date list keeps the last few weeks available. The site has no adverts and needs no account.

It suits sudoku players who like a bit of arithmetic and want a set of graded grids each day.