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📖 How to Play Kakuro
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Kakuro cross-sums puzzle — fill every white cell with digits 1–9 so each run sums to its clue with no repeats. 5 grid sizes from 6×6 to 10×10, 7 difficulty levels from Beginner to Cyborg, daily challenge.
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.
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.
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.
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.
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. Not every tier is offered at every grid size — the difficulty list changes with the grid, and shows only the tiers that size can actually deliver, so the board you get is always the one you asked for.
Play Kakuro free in your browser — no download, no sign-up. Five grid sizes, up to seven difficulty tiers each, 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.
Kakuro taught me a lesson about engineering honesty that I now apply to every generator on this site. Early builds could hang the main thread while hunting for a guaranteed-unique large board — and a freeze of around 1.2 seconds, in a browser game, reads as a crash. Players don't see mathematical rigor; they see a page that stopped responding. So I made a deliberate trade: generation runs on a wall-clock budget, and if the budget expires, the generator accepts a rare non-unique board at the same size rather than ever freezing. Nobody notices a second valid solution. Everyone notices a hang. I stand by that call completely, and I'd rather say it here in plain words than pretend the trade-off doesn't exist.
The harder design problem, honestly, wasn't generating valid puzzles at all. It was making sure every board gives you real entry points — cells you can start solving from without guessing. A technically-correct Kakuro with no foothold is just a wall of white cells daring you to gamble. Getting the clue structure to offer a few forced openings, on every board, at every size, took longer than the solving engine itself did.
Those entry points come from the game's most beautiful property, and it's exactly the one newcomers ignore. Every run must hit its sum with unique digits, and that combination forces cells far harder than people expect. A three-cell run summing to 6 has exactly one digit set: 1, 2, and 3. A two-cell run summing to 3 must be 1 and 2. A two-cell run to 17 must be 8 and 9. These aren't clever deductions — they're the only possibilities that exist. And yet I watch players brute-force their way through cells the sum-combination already determined, testing digits one by one in a run that mathematics settled before they ever touched the board.
So here's how to actually start. Scan for the extreme runs first — the lowest sums in two cells, then the highest, then the forced three-cell sets like 6 and 24. Pencil those candidate sets in. Where two forced runs cross, the shared cell often collapses to a single digit immediately, and that one digit ripples outward through both runs, resolving neighbours you haven't even looked at yet. That cascade is the game. The feeling of one placement unlocking six others is why this puzzle has survived since the pencil-and-paper era, and it's what I wanted the browser version to preserve above everything else.
Play the small boards until the standard sum-sets live in your memory the way multiplication tables do. After that, the big grids stop being intimidating and start being long, pleasant walks. The daily resets at midnight — every player worldwide gets the same board, entry points and all.