The goal of the game is to fill all the white cells using the digits 1 to 9.

the black cells contain hints – the number in the black cell is the sum of the block of white cells associated with it

we’ll start in the upper left side. the number 4 which is in the upper right section of the black cell is the sum of the horizontal block of white cells associated with it.

the block has 2 cells and 3+1=4.

the number 3 which is in the lower left section of the black cell is the sum of the vertical block of white cells associated with it.

the block has 2 cells and 1+2=3

you cannot user the same digit twice in the same block!

Therefore this 3 cannot be {2,1}

it has to be {1,2}

which makes this 3 to be {1,2}

and if you put 5 in the middle it’ll all fit – 8=2+5+1 and 9 = 3+5+1.

Kakuro has unique combinations and it’s easy to start the game searching for them. for example:

in 3 cells, the sum 6 has to be the digits {1,2,3} the sum 24 has to be {7,8,9}, you still have to determine the order of the digits in the block.

click on Blocks on the main page of Online Kakuro and you’ll see a list of unique Kakuro blocks

you can also check the combinations link on the main page to see a list of all possible combinations for Kakuro Blocks (not just unique).

That’s all there is. How hard can it be? Be warned it gets hard and is as addictive as Sudoku.