Daily Killer Sudoku (SudokuWiki)

SudokuWiki.org is Andrew Stuart's site about sudoku solving strategies and solvers, and the Daily Killer Sudoku is one of its long-running daily puzzles, past number 6,700 by October 2026.

A killer sudoku has the normal sudoku rules, with 1 to 9 once in every row, column and 3x3 box, but few or no given digits. Instead the grid is divided into cages outlined with dotted lines, each with a small number showing the sum of its cells, and no digit may repeat inside a cage. Solving relies on cage sum combinations as much as on sudoku logic.

The daily follows a weekly cycle: Monday and Tuesday are Gentle, Wednesday and Thursday Moderate, Friday Tough, and Saturday and Sunday Diabolical. The page says the new puzzle arrives at midnight GMT, but in practice the previous day's grid stays up until about 03:00 to 03:15 UTC. The player supports notes, prefilling candidates, automatic clearing of notes, keyboard shortcuts, undo and redo, colour options and links to print or open the puzzle in the killer solver. A 30-day calendar beside the board lists recent puzzles and their solutions, and All-Access supporters can play all four grades each day.

It suits sudoku players who enjoy arithmetic as well as logic, and the weekly difficulty curve lets newcomers start early in the week.