Kakuro is the Japanese cross-sums puzzle — a logic game that looks like a crossword but is built entirely from arithmetic. The grid is split into black clue cells and white input cells. Your job is to fill every white cell with a digit from 1 to 9 so that each run of consecutive whites adds up to its target clue, with no digit repeating inside a single run.

🔢 Reading the Clues

Every black cell that borders a white run carries one or two numbers split by a diagonal. The number in the top-right triangle is the sum for the run going across to its right. The number in the bottom-left triangle is the sum for the run going down below it. Tap any clue to see all valid digit combinations that fit — the combo helper greys out any combination already ruled out by what you've placed.

🧠 The Logic of It

Kakuro lives on two intersecting constraints: every cell sits on both an across run and a down run, and each run forbids repeats. That means a short, extreme sum often resolves itself instantly — a 2-cell run summing to 3 can only be 1+2; a 2-cell run summing to 17 can only be 8+9. Those forced cells then constrain the runs crossing them. Find the locked combos first and let the cascade do the work.

✏️ Notes & Tools

Toggle ✏️ Notes in the toolbar to pencil in candidate digits as small marks — useful when a cell could be 2 or 3 things and you want a record. Hit 💡 Hint if you're truly stuck (it fills one cell with the correct digit but adds 30 seconds to your time). Use ↶ Undo to roll back. Hit ✓ Check any time to flash wrong entries in red — it costs nothing and disappears after 3 seconds.

⚡ Grid Size & Difficulty

Grids run from 6×6 (compact, fast) to 10×10 (long, contemplative). Difficulty ramps from Beginner (short runs, many unique combos, gentle layout) up through Cyborg ☠ (long runs, dense layouts, multiple valid combinations per clue). Daily challenges run at Medium so every player has a fair shot.

Play Kakuro free in your browser — no download, no sign-up. Five grid sizes, seven difficulty tiers, a seeded daily challenge that's the same for every player worldwide, and shareable challenge links so you can send your best time to friends and see if they can beat you.

Kakuro was invented in 1966 by Canadian Jacob Funk for Dell Magazines as "Cross Sums." Japanese publisher Nikoli rebranded it as "Kakuro" (a contraction of kasan kurosu, "addition cross") in the 1980s and it became a phenomenon — second only to Sudoku in Japan's puzzle pantheon. This version preserves the original mechanics with combo-biased puzzle generation that guarantees every layout is logically solvable, plus the modern conveniences: notes, hints, undo, check, daily streak.

• Memorise the unique combos first. A 2-cell run summing to 3 is {1,2}. A 3-cell run summing to 7 is {1,2,4}. A 3-cell run summing to 24 is {7,8,9}. These cells fill themselves.
• Hunt for intersections of short runs. Where a tight across-clue meets a tight down-clue, the cell often has only one digit that satisfies both.
• Subtract to finish a run. When a run has one empty cell left, the missing digit is just clue − (digits already placed). No guessing needed.
• Use the combo tooltip. Tapping a clue reveals every valid combination. As you fill cells, impossible combos cross out — letting you see what's still on the table.
• Pencil notes for high-density grids. On Scientist and Cyborg layouts you'll have cells with 3-4 possibilities. Pencil them in so you don't lose track when crossings narrow them down.
• Save Check for when you're stuck. Don't burn it on every cell — use it when you suspect a contradiction and need to find where you went wrong.