How to play
Kakuro is a crossword made of numbers. The grid has dark clue cells and white cells. Every unbroken line of white cells, across or down, is a run, and it starts right after a clue cell. The number in the upper right half of a clue cell is the total for the run to its right; the number in the lower left half is the total for the run below it. Fill every white cell with a digit from 1 to 9 so that each run adds up to its clue and no digit appears twice in the same run.
Pick a size and a level, press Start, select a cell and enter a digit. The clock stops when you pause or switch tabs, and your puzzle, notes and undo history are saved in this browser.
Controls
- Mouse: click a cell, then a digit on the number pad. Clicking a clue cell jumps to the first cell of its run.
- Touch: tap a cell, then a digit. On big grids, Zoom in makes the cells finger sized; drag inside the board to move around.
- Keyboard: arrow keys move, 1–9 enter a digit, Backspace, Delete or 0 clear it, N switches notes, Shift plus a digit writes a note, Z undoes, Y redoes, H gives a hint, C checks, P pauses and F toggles full screen.
With notes on, digits go in as small pencil marks, and entering a real digit removes the same note from the rest of its runs. Check marks every wrong entry with a red slash. Hint fills the selected cell if it is empty or wrong, otherwise the empty cell with the fewest possible digits; hint cells are locked and get a green corner. A digit repeated in a run gets a red background, and the clue of a full run with the wrong total gets a wavy underline.
The combination helper
For the selected cell, the panel lists every set of different digits that can make each of its two runs. A set is struck out when it lacks a digit already entered in another cell of that run. “Fits here” shows the digits that belong to a remaining set of both runs and are not used elsewhere in them.
How it works
For a run of k cells the lowest possible total is 1 + 2 + … + k and the highest is 9 + 8 + … + (10 − k):
lowest = k(k + 1) / 2 highest = k(19 − k) / 2
Totals at both ends of that range have exactly one combination: 3, 4, 16 and 17 for two cells (3 is always 1 + 2), 6, 7, 23 and 24 for three cells, 10, 11, 29 and 30 for four. Every total of eight cells is unique, since eight different digits are all nine minus one. Middle totals are the most open: 20 in four cells and 25 in five can each be made in 12 ways.
The puzzles were made in advance. A program draws a symmetric grid, fills it without repeats, computes the clues and searches for a second solution; if one exists, it changes a digit where the two solutions differ and tries again. A separately written solver then confirmed that every puzzle here has exactly one solution. A grading solver sets the level: Easy puzzles can be finished cell by cell from the combinations of the two runs through each cell, Medium ones also need you to test whether a whole run can still be completed, and Hard ones need at least one step of “what if” – try a candidate and watch it break a run.
Each of the 60 stored puzzles per size and level can also appear mirrored along the diagonal, or with every digit d replaced by 10 − d (a run of k cells with total S then totals 10k − S). Neither changes the solution count or the logic needed, so each choice offers 240 puzzles. In all, the page can show 2,880 puzzles (720 stored puzzles in four versions each), and two independent solvers checked every one of them.
Tips and strategy
- Start with runs that have only one combination, such as 3 or 17 in two cells, 6 or 24 in three, or 45 in nine.
- Look where two runs cross. A cell in both “3 in 2” (1 and 2) and “4 in 2” (1 and 3) can only be 1.
- Big totals rule out small digits: 23 in three cells needs 6, 8 and 9, so no cell of that run can hold a 7 or less.
- When all but one cell of a run is filled, the last digit is the total minus the rest.
- Use notes on crossing cells and watch for two cells of a run with the same two candidates.
Frequently asked questions
What does the size mean?
It counts the whole grid, including the clue cells along the top and left. A 6×6 puzzle has about 17 white cells, a 12×12 puzzle about 77.
Why can a digit repeat in a row?
The no-repeat rule applies only within one run, and a clue cell in the middle of a row splits it into two runs.