Rocket Kakuro: Kakuro Cross Sums

What is Rocket Kakuro?

Rocket Kakuro is the cross sums puzzle, free in your browser on phone, tablet or computer. It plays like a crossword made of numbers: every run of white cells has a clue, and you fill the run with digits from 1 to 9 that add up to that clue without using any digit twice. A new daily puzzle arrives every midnight, the same for everyone, and you can build as many fresh grids as you like from a quick 6×6 to a sprawling 14×14.

There are four levels, graded by the logic a puzzle needs rather than its size. Easy falls to unique sums and crossing runs, Medium asks you to weigh sum combinations, Hard needs cross-elimination between runs, and Expert brings in short what-if chains. Every grid is built on the spot, has exactly one solution and never needs a guess. A combination helper lists every way to make the selected cell's sums, pencil-mark notes and auto-candidates keep track of the options, and hints explain the next deduction instead of just filling in a number.

How to play Rocket Kakuro

1. The goal: fill every white cell with a digit from 1 to 9 so each run adds up to its clue and no run repeats a digit.
2. Clues sit in the dark cells. The number above the diagonal is the sum of the run to its right; the number below the diagonal is the sum of the run beneath it.
3. Tap or click a white cell (or move with the arrow keys), then tap a number or type 1 to 9. The cell's across and down runs light up and their clues turn gold.
4. Check the combination helper under the grid: it lists every set of digits that makes each of the cell's sums, strikes out sets your digits rule out, and shows the digits every remaining set needs.
5. Turn on Notes (or press N) to pencil in candidates, or switch on Auto-candidates in Settings. Wrong digits turn red if you like, and Hint fills one cell and explains why. Fill the last cell to finish.

Rocket Kakuro tips and strategy

• Learn the unique sums. 3 in two cells is always 1+2, 4 in two is 1+3, 16 in two is 7+9 and 17 in two is 8+9; in three cells 6 is 1+2+3, 7 is 1+2+4, 23 is 6+8+9 and 24 is 7+8+9.
• Where an across run and a down run with few combinations cross, the shared cell can only hold a digit both allow. These crossings break most Easy grids open.
• Watch for digits every combination needs: if 10 in four cells must be 1+2+3+4, a 4 has to go somewhere in that run, and often only one cell can take it.
• Big digits can't go in small runs: a cell in a run of 4 in two cells can never be more than 3, which in turn limits the run crossing it.
• Finish a run as soon as only one cell is left: its digit is the clue minus the digits already in.
• On Hard and Expert grids, turn on Auto-candidates to skip the bookkeeping and look for the cross-eliminations and chains.

Kakuro rules

A Kakuro grid mixes dark clue cells with white cells. Each horizontal or vertical run of white cells has a clue, the sum its digits must make. You write a digit from 1 to 9 in every white cell so that every run adds up to its clue and no digit appears twice in the same run. A digit can repeat in a row or column as long as it is in different runs.

A good Kakuro has exactly one solution and can be solved by logic alone. Every Rocket Kakuro grid is checked twice before you see it: our step-by-step solver finishes it with human techniques, which proves the solution is unique, and an independent search confirms there is no second solution.

Kakuro combinations: the combination helper

Kakuro is about combinations. A run of two cells adding up to 4 can only be 1 and 3; a run of five cells adding up to 35 can only be 5, 6, 7, 8 and 9. Most sums have several combinations, and the art is finding which one fits the crossing runs.

Rocket Kakuro shows them for you. Select a cell and the combination helper lists every set of digits that makes its across sum and its down sum, crosses out the sets your digits have already ruled out, and shows the digits every remaining set needs. It's a learning aid you can switch off in Settings once the common sums are second nature.

Difficulty levels and grid sizes

Easy grids need only unique sums and crossings: cells where an across run and a down run together leave one digit. Medium needs sum combinations, keeping only the sets that fit the digits a run's cells can still hold. Hard needs cross-elimination, placing each combination cell by cell against the crossing runs (pairs and triples inside a run). Expert needs chains: suppose a digit, follow the consequences, and rule it out when they break.

Pick any size from 6×6 to 14×14 at any level: small grids make a coffee-break puzzle, big ones a long session with zoom and pan. Leaderboard times are kept for Easy 8×8, Medium 10×10, Hard 10×10 and Expert 12×12, the same sizes as the daily puzzles.

The daily Kakuro

The daily puzzle changes at midnight and is the same for every player. Its level follows the week: Monday is Easy, Tuesday, Wednesday and Friday are Medium, Thursday and Saturday are Hard and Sunday is Expert. Solve it on its day to build your streak, see your solved days on the calendar, and play any past day you missed.

Rocket Kakuro FAQ