Press Hint for one cell, or Solve to reveal everything.
How a Kakuro solver works
A solver treats the puzzle as a constraint problem. Each white cell starts with the candidate set 1 to 9. Two constraints then do the work: every run's digits must be distinct, and they must sum to the clue. From those, the solver repeatedly prunes candidates.
Constraint propagation
For each run, the solver computes which digit combinations are still possible for its clue and length, then removes any candidate that no surviving combination uses. When a cell is reduced to a single candidate, that digit is removed from every other cell in both of its runs, which often triggers a cascade of further reductions. Many easy and medium puzzles fall to propagation alone, with no guessing.
Backtracking search
When propagation stalls, the solver picks the most constrained cell, the one with the fewest candidates, and tries each in turn. After each trial it propagates again; if a run becomes impossible (a contradiction), it undoes the choice and tries the next. This depth-first search with propagation is fast because the constraints prune the tree aggressively. The same routine also lets the generator confirm a puzzle has a single solution.
Practise the technique by hand
The fastest way to need the solver less is to learn the human methods on the strategy page and keep the combinations reference handy. Then test yourself on a fresh puzzle.
Frequently asked questions
Can this solve any Kakuro?+
The built-in solver completes the puzzles generated on this site. Press Hint to reveal a single correct cell when you are stuck, or Solve to reveal the whole grid. A paste-in solver for puzzles from other sources is on the roadmap.
How does a Kakuro solver work?+
It assigns each white cell a candidate set of digits, then prunes those sets using the rules: a run's digits must be distinct and sum to its clue. Where a cell has one candidate left it is fixed, which prunes its neighbours. When deduction stalls it backtracks, trying a candidate and undoing it if it leads to a contradiction.
Is using a solver cheating?+
It is your puzzle, so use it however you like. Most players use Hint to break a single blockage and learn the technique they missed, then finish the rest themselves. Auto-solve is there for when you simply want to see the answer.