A crossword with digits: every run must add up to the number in front of it, without repeating a digit.
Hunt for runs with only one possible combination. Two cells adding to 3 must be 1 and 2. Three cells adding to 6 must be 1, 2 and 3. Four cells adding to 30 must be 6, 7, 8 and 9. Where such a run crosses another, the intersecting cell often has just one digit that works in both.
Knowing the combination is not the same as knowing the order. Fill a cell only when the crossing run leaves exactly one option.
Each kakuro in Puzelo is checked by a solver written separately from the generator, using a different method. A puzzle is only published if that independent solver finds exactly one solution — so you never need to guess, and the answer we print is never wrong.
More puzzle types: Sudoku · Nonogram · Binary Puzzle · Futoshiki