Sudoku with no givens: fill 1 to 9 so every row, column and box is complete and every dashed cage adds up to its total
Killer sudoku keeps the ordinary sudoku rule, 1 to 9 exactly once in every row, column and 3×3 box, but starts with an empty grid. Instead of given digits, the grid is split into cages drawn with dashed lines, and each cage shows the total its digits must add up to. No digit may repeat inside a cage. Ours builds a new puzzle every time you press New, at three levels, and checks each one with a solver before showing it: if a second answer exists, a cage is split into two smaller ones until only one answer is left.
Pick a level. Easy uses cages of up to three squares, medium up to four and hard up to five.
Press New puzzle. Each dashed outline is a cage; the small number in its top-left corner is the total its digits must reach.
Tap a square, then tap a number on the pad to write it. Clear removes it.
Under the grid, the helper lists every set of different digits that can make the selected cage's total, for example 3 in 2 is 1+2 only.
On a keyboard, move with the arrow keys, type 1 to 9, and press Backspace to clear. Ctrl+Z undoes.
With Show clashes on, a digit that repeats in a row, column, box or cage turns red, and so does a cage whose digits go over its total or finish on the wrong one.
Fill all 81 squares correctly and the puzzle ends; your time is saved as a best for that level.
Arithmetic under constraints and structured deduction. Each cage is a small sum you solve by listing which sets of different digits can reach the total, then narrowing that list with the row, column and box rules. Good solves also lean on a counting fact: every row, column and box adds to 45, so the part of a cage that sticks out of a box can be worked out by subtraction. It is mental arithmetic that has to be exact, combined with the bookkeeping of ordinary sudoku.
Learn the one-answer cages: 3 in two squares is always 1 and 2, 4 in two is 1 and 3, 16 in two is 7 and 9, 17 in two is 8 and 9, and 6 in three is 1, 2 and 3.
Use the helper under the grid. When it shows a single set of digits, those digits must go in that cage in some order.
Every row, column and box adds up to 45. If the cages inside a box total 38 and one square of the box is outside those cages, that square is 7.
The same trick works across several boxes: three full rows add up to 135.
A cage of one square is just a given digit. Write it in straight away.
Leave Show clashes on while you learn; turn it off for a harder solve where only the finished grid tells you whether you were right.
Killer sudoku is sudoku with sums. The usual rule still applies: each row, column and 3×3 box contains 1 to 9 once. The grid also has cages, groups of squares marked with dashed lines, and the digits in each cage must add up to the number in its corner with no digit repeated inside the cage. There are no starting digits; the totals are the only clues.
No. A digit may appear only once in a cage, even when the cage crosses from one box into another.
Yes. Before a puzzle is shown, a solver searches for a second answer. If it finds one, the generator splits a cage where the two answers differ and checks again, and it repeats until only one answer is possible.
The largest cage size. Easy grows cages of up to three squares, medium up to four and hard up to five. Larger cages have more digit sets that reach the same total, so they take more reasoning to pin down.
For the cage of the square you have selected, it lists every set of different digits from 1 to 9 that adds up to the cage's total with the right number of squares. It does not look at the rest of the grid, so some of those sets may already be ruled out.
Because each of the nine rows adds up to 1 + 2 + … + 9 = 45, and 9 × 45 = 405. Every square is in exactly one cage, so the cage totals add up to the same 405.
It is free with no sign-up. Your best time for each level, your number of solved puzzles and the Show clashes setting are saved in this browser only.