Kakuro - Free Online Number Crossword Puzzle

Select a white cell, then enter a digit

About Kakuro Puzzle Online — Kakuro Puzzle Online

Kakuro puzzle online is often called the "number crossword" because it merges the structure of a crossword grid with arithmetic constraints. Black cells divide the grid into white "runs" — consecutive sequences of empty cells. Each run has a clue number printed in an adjacent black cell: this number is the exact sum that the digits in that run must total. Fill every white cell with a digit from 1 to 9 so that each run sums to its clue, with no digit repeated within any single run. Every cell satisfies both a horizontal across constraint and a vertical down constraint simultaneously.

Kakuro originated in Japan and was popularised by puzzle publisher Nikoli, which standardised the format and published it widely in Japanese puzzle magazines from the 1980s onward. The puzzle is deeply rooted in mathematical logic: each clue constrains both the sum and the composition of its run. A clue of 3 for a two-cell run, for instance, can only be filled with the digits 1 and 2. This candidate-restriction technique is the core analytical tool used by Kakuro solvers at every level.

Controls

Click a white cell — Select it for digit input (selected cell highlights in blue)
Number keys 1–9 — Enter a digit into the selected cell
Delete / Backspace — Clear the selected cell
Arrow keys — Move the selection to an adjacent white cell
On-screen numpad — Tap digits 1–9 or the ✕ erase button on touch devices
Check button — Highlight correct cells in green and errors in red

How to Play Kakuro Puzzle Online

Each kakuro puzzle online has exactly one valid solution reachable through logical deduction — no guessing is needed.

Read the clue cells: Black cells that contain numbers are clue cells. A number in the lower-right triangle of a clue cell is an "across" clue — the sum of the white cells immediately to its right. A number in the upper-left triangle is a "down" clue — the sum of white cells directly below it. A clue cell can have both an across and a down clue, or just one.
Identify forced combinations: Many sum-and-length combinations have only one possible set of digits. A run of 2 cells summing to 3 must be {1, 2}. A run of 2 cells summing to 17 must be {8, 9}. A run of 9 cells summing to 45 must contain all digits 1 through 9. Memorising or deriving these forced combinations is essential for making early progress.
Apply the no-repeat rule: No digit may appear twice within a single run. When a run's candidate digits are narrowed to two options, and one of those digits already appears elsewhere in the same run, the other digit is confirmed. Cross-checking across and down runs with this rule eliminates candidates rapidly.
Cross-reference perpendicular runs: Every white cell belongs to exactly one across run and one down run. A digit candidate eliminated from the down run automatically removes it from the across run's possibilities for that cell, and vice versa. Always re-examine both runs through a cell after any new deduction about it.
Use the Check button strategically: Press Check after completing a section of the grid to confirm your progress before continuing. Seeing which cells are correct (green) versus incorrect (red) focuses your attention on the region where a logical error was made rather than requiring you to recheck the entire puzzle.

The puzzle is solved when every white cell contains a correct digit and all runs sum exactly to their clues with no repeated digits.

Tips & Strategies for Kakuro Puzzle Online

These techniques apply directly to the 5×5, 6×6, and 7×7 puzzles in this kakuro puzzle online collection.

Start with uniquely determined runs: Look for runs where the clue and length combination has only one valid digit set. A 3-cell run summing to 6 must be {1, 2, 3}; a 2-cell run summing to 16 must be {7, 9}; a 4-cell run summing to 10 must use digits from a very limited set. These force placements in specific cells and give you confirmed digits to cross-reference everywhere else.
Build combination tables mentally: With practice, you will memorise the most common forced combinations. Key examples: sum 3 in 2 cells = {1,2}; sum 4 in 2 cells = {1,3}; sum 16 in 2 cells = {7,9}; sum 17 in 2 cells = {8,9}; sum 6 in 3 cells = {1,2,3}; sum 23 in 3 cells = {6,8,9}. Recognising these instantly accelerates solving time significantly.
Use the intersection of across and down constraints: When an across run has two candidate digits for a cell and the down run through that same cell can only contain one of those digits, the correct digit is pinned immediately. This intersection technique resolves ambiguous cells without requiring any guessing.
Work on runs with the fewest remaining cells first: A run with only one empty cell has no flexibility at all — you simply subtract the sum of filled cells from the clue to find the missing digit. Always resolve these single-remaining-cell runs before touching more open runs.
Track pencil candidates mentally: For each unfilled cell, track which digits remain possible given both the across and down run constraints. When a cell's candidate list narrows to one digit, fill it immediately. Then update the candidate lists of all other cells in both runs through that cell.

Skills You Develop Playing Kakuro Puzzle Online

Kakuro puzzle online builds arithmetic reasoning within a logical deduction framework. Unlike Sudoku, which requires only placement logic with no arithmetic, Kakuro demands simultaneous management of sum constraints, digit restrictions, and cross-run interactions. Regular solving develops mental arithmetic fluency — specifically the ability to quickly decompose target sums into valid digit combinations — as well as the methodical constraint-satisfaction thinking that underlies mathematical proof and algorithm design.

Pattern recognition improves with sustained Kakuro play as solvers internalise the catalogue of unique sum-length combinations. This mental library reduces the analytical load on each new puzzle. The dual-constraint nature of every cell — belonging to both an across and a down run — trains attention to multi-dimensional dependencies, a skill that transfers to spreadsheet analysis, database queries, and any domain requiring simultaneous satisfaction of multiple conditions.

Frequently Asked Questions about Kakuro Puzzle Online

A run is a consecutive, uninterrupted sequence of white cells in a single row or column, bounded by black cells or the grid border on both ends. Every run has exactly one clue — either an across clue (for horizontal runs) or a down clue (for vertical runs). Each white cell belongs to exactly two runs: one horizontal and one vertical. Your digit entry must satisfy both runs simultaneously.

No — within any single run, each digit 1 through 9 may appear at most once. A run of length 3 summing to 9 cannot be filled with {3, 3, 3} even though 3 + 3 + 3 = 9. It must use three distinct digits that sum to 9, such as {1, 2, 6}, {1, 3, 5}, or {2, 3, 4}. This no-repeat rule combined with the sum constraint dramatically reduces the number of valid digit combinations for each run.

Clue cells are black cells with numbers divided by a diagonal line. The number in the lower-right triangle is the across clue — the sum of all white cells immediately to the right of this clue cell in the same row. The number in the upper-left triangle is the down clue — the sum of all white cells immediately below this clue cell in the same column. A clue cell may have one or both clue numbers, depending on whether it borders an across run, a down run, or both.

Yes — all 10 puzzles in this kakuro puzzle online collection are handcrafted to have exactly one valid solution reachable through pure logic without guessing. If at any point you feel you need to guess, it is a signal to return to unfilled cells and look more carefully at the intersection of their across and down run constraints. There is always a logical deduction available that uniquely determines a cell.

The most immediately useful technique is learning the uniquely determined combinations — run lengths and sums where only one valid digit set exists. Examples: a 2-cell run summing to 3 can only be {1,2}; summing to 17 can only be {8,9}; a 3-cell run summing to 6 can only be {1,2,3}; summing to 24 can only be {7,8,9}. Committing a dozen of these to memory lets you immediately confirm digits in constrained runs and begin cross-referencing from there.

Sudoku and Kakuro are both number placement logic puzzles, but they differ fundamentally in their constraints. Sudoku uses fixed 9×9 regions with no arithmetic — only placement uniqueness within rows, columns, and 3×3 boxes matters. Kakuro uses variable-length runs with an exact sum requirement, meaning arithmetic reasoning is central rather than incidental. Kakuro grids are also irregular, with black cells placed at varied positions rather than following a fixed pattern, making each puzzle structurally unique.

Pressing Check compares every filled white cell against the puzzle solution. Cells containing the correct digit are highlighted green; cells with incorrect digits are highlighted red; unfilled cells are not affected. You can press Check at any point during the solve — it does not reveal the solution, only whether your current entries are right or wrong. Use it after completing sections you are confident about to confirm them before moving on to harder regions.

Yes — the game includes an on-screen numeric keypad designed for touch input. Tap any white cell to select it (it highlights in blue), then tap a number button on the numpad to enter that digit, or tap the ✕ button to erase it. Arrow key navigation is also supported on keyboards. The grid and numpad scale responsively to the available screen width, making the puzzle fully playable on smartphones and tablets without zooming.