Kakuro, also called Cross Sums, is a crossword made of numbers. Instead of words you write digits from 1 to 9, and instead of definitions each clue gives the sum of a run of squares. Every puzzle here has exactly one solution and can be solved by reasoning, without guessing.
Write one digit from 1 to 9 in every white square. A clue square is split by a diagonal: the number above the diagonal is the sum of the white squares to its right, and the number below it is the sum of the white squares beneath it. Each unbroken line of white squares is a run.
Within a run, a digit can be used only once, so a run of two squares adding up to 4 must be 1 and 3, never 2 and 2. The same digit can appear again in a different run.
Some sums can be made in only one way. Learn them and look for them first: where two runs with few combinations cross, the shared square often has only one possible digit.
Start where an across run and a down run share only one digit: if the across run can only use 1 and 3 and the down run can only use 3, 5 and 7, the square where they cross must be 3.
Once a digit is placed, remove it from the rest of its runs. Large sums limit the small digits: a run of three squares adding up to 22 can never use 1, 2, 3 or 4. Use Pencil to keep track of the candidates, and turn on Combinations to list every way to make a sum.
On harder grids, follow one candidate: if putting 2 in a square leaves another run with no possible combination, that square cannot be 2.
Choose a puzzle from 3 × 3 to 10 × 10. As on most Kakuro sites, the size counts the area of white squares; the grid adds a row and a column of clues, so a 6 × 6 puzzle is a 7 × 7 grid. Larger puzzles need more reasoning. 3 × 3, 4 × 4 and 6 × 6 can be solved by crossing combinations alone. 8 × 8 asks you to look at a whole run, for example two squares that must share a pair of digits. 10 × 10 sometimes asks you to follow a candidate until it leads to a contradiction. Every puzzle is checked by computer for a single solution and for the reasoning its size needs.
Yes. Each puzzle is solved by computer using only logical steps before it is added, which also proves that no second solution exists.
Not within the same run. The same digit can appear in different runs, including runs that do not cross.
Kakuro uses the digits 1 to 9 only, so a run can hold at most nine squares and its sum is between 3 and 45.
Both use the digits 1 to 9 without repeats, but Kakuro has no fixed rows of nine: its clues are sums, so arithmetic and combinations decide each square.
Yes. There is no account and nothing to install, and the puzzles are checked in your browser.
Kakuro