How do you play Killer Sudoku?

It is Sudoku with sums instead of given digits. Every row, column and 3 by 3 box holds the digits 1 to 9 once. The grid is also split into cages, drawn as dashed outlines with a small sum in the corner of each: the digits in a cage add up to that sum, and a cage never repeats a digit, even when its squares sit in different rows and columns. A two-square cage with sum 3 can only hold 1 and 2, in either order; 2 and 2 would add up to 4 but is never allowed. All the cage sums together always total 405, because each of the nine rows adds up to 45. The board here counts as solved only when every square is filled and every rule holds.

Does every Killer Sudoku here have exactly one solution?

Yes. Each puzzle starts from a complete, valid grid that a seeded search fills in. Every square begins as a cage of its own, squares left alone are joined to a neighbour first, and after that cages are joined two at a time in a seeded order, up to five squares each and never so that a cage would hold the same digit twice. After every join a solver narrows the digits each square can take and then searches on past the first solution for a second one. The join is kept only when it proves there is exactly one; a join it cannot settle within 3,000 steps is refused, not kept. Joining stops when the puzzle reaches a cage count its seed draws between 26 and 30, or when no join passes. If a build spends 60,000 steps first, leaves a square with no cage to join, or ends with more than 30 cages, the page opens one of 12 fixed seeds whose puzzles a separate brute-force solver has checked, and says why and which seed it opened.

What does the small number in a cage mean?

It is the cage's sum: the digits in the squares inside that dashed outline add up to it. The number sits in the cage's first square, reading left to right from the top row. The side pane lists every cage with its sum as text, and when you select a square it names the square's cage, how many squares it has, its sum and the digit sets that still fit it, given the digits already in its rows, columns and boxes. A screen reader hears the cage letter, its size and its sum for every square.

Press Notes under the grid, or N on a keyboard, and the digits add or remove small pencil notes in the selected square instead of filling it. Press it again to go back to digits. Notes only go in empty squares, and typing a digit into a square clears its notes. Notes never count as filled squares or as a solution: a board full of notes is still an empty board. They are saved with your progress, and Undo takes them back like any other move.

What do Check, Reveal cell and Hint do?

Check compares every digit you typed with the puzzle's one solution and outlines the ones that differ until your next move. Reveal cell fills the selected square from the solution and locks it. Hint looks at the board in order: a digit twice in a row, column or box; a cage with a repeat or a total it can no longer reach; a digit that breaks no rule but is not part of the solution; then a square with only one digit left, with the reason each other digit is out, or a digit with only one place left in a row, column or box. If none of those settles anything, it names one answer in words. Hint never types a digit for you. Every check of your digits, every reveal and every hint marks the game assisted, the status shows how many of each you used, and Undo does not remove that mark. A clash you type yourself is marked red by the rules alone and is not an assist.

Can I print a Killer Sudoku puzzle?

Yes. Print puzzle prints the grid with its dashed cages and sums, headed with the seed and the cage count, with the rules underneath; tick the box under the tool to add the answer key on a second page. Print answer key prints the solved grid alone, with the same cages and sums. The grid prints 162 mm square. Copy puts the puzzle on the clipboard as text instead: a cage letter for every square with your digits, then every cage's sum.

What is the seed, and can I play the same puzzle again?

The seed is a whole number from 1 to 999999. The build draws its random numbers from a fixed formula seeded by it and counts the solver's steps rather than timing them, so the same seed makes the same puzzle on any device. The seed of the puzzle on the board is shown above the grid and in the Seed box. To open a puzzle again, type its seed and press Play seed. New puzzle picks a random seed.

Is my progress saved, and is there a timer?

Progress is saved in this browser only: the puzzle on the board, your digits and notes, revealed squares, how many checks, reveals and hints you used, and the timer, along with up to 9 earlier puzzles you left with a digit, a note or an assist used. A saved game reopens only when its seed rebuilds exactly the same cages and sums; an edited save is refused and the page says so. Undo reaches back through up to 400 moves made since the puzzle was opened in this visit. The timer is off until you switch it on; it then counts while the tab is visible and the puzzle is unsolved. Nothing is uploaded, and the Start over button at the top of the page forgets all of it. If the browser refuses storage, the side pane says the puzzle is not being saved, and it still plays.

Killer Sudoku

Fill the grid so that every row, column and 3 by 3 box holds 1 to 9 once, and the digits inside each dashed cage add up to the small sum in its corner without repeating. There are no given digits: the cage sums are the only clues. Every puzzle here is original and built on this page from its own solved grid. Each square starts as a cage of its own, cages are joined two at a time, and a join is kept only after a solver proves the puzzle still has exactly one solution, so what you get is a grid of 26 to 30 cages of 2 to 5 squares. The label on a puzzle counts its cages instead of claiming a difficulty. Tap a square and type a digit, or use the pad under the grid, which also moves between squares at phone size; Notes switches the digits to pencil notes. A square turns red the moment its digit repeats in a row, column, box or cage, or its cage can no longer reach its sum, and the side pane lists the digit sets that still fit the selected cage. Check, Reveal cell and Hint are there when you want them, and each marks the game assisted. Undo and redo, an optional timer, progress saved in this browser, and print for the puzzle and its answer key round it out.

puzzleno puzzle yet

Setting up the board

Your saved puzzle, or a new one, appears here in a moment.

cagessaved once you play

rules: Each row, column and 3 by 3 box holds the digits 1 to 9, each once. The digits in each dashed cage add up to the small sum in its corner, and a cage never repeats a digit.
sums: none yet
status: none yet
timer: off
keys: arrows move, 1 to 9 enter, N notes, Delete erases

Setting up the board.

Filled

none yet

Cages

none yet

Notes

none yet

Status

none yet

Seed

Print puzzle adds the answer key on a second page

Tap a square, or move to it with the arrow keys, then type a digit or press one on the pad under the grid. Notes (or N) switches the digits to notes and back; notes never count as filled squares. Delete, Backspace or 0 erases, and Ctrl+Z or Cmd+Z undoes. A square turns red the moment its digit repeats in a row, column, box or cage, or its cage can no longer reach its sum. Check compares your digits with the solution, Reveal cell fills the selected square from it, and Hint names a clash or a broken cage first, then a digit that is not part of the only solution, then the next square you can work out and why; each of these marks the game assisted, and undo does not remove the mark. The seed on the board makes the same puzzle again anywhere, and your progress stays in this browser.

Your recent puzzles

No earlier puzzles yet. Each puzzle you leave with a digit, a note or an assist used is kept here with its seed and your progress, up to 9, so you can go back to it.

How the rules are checked

Two-cell cage, sum 31 and 2, or 2 and 1
the only fill; 2 and 2 fails even in a sum 4 cage, since a cage never repeats a digit
Reveal one cellany empty cell
the answer is filled in and locked, and the puzzle is marked assisted; undo removes the digit, not the mark
Save, reload or print31 digits and 2 cells of notes
the same cages and sums; notes stay notes and never count as solved digits

Accuracy. Every row, column and 3 by 3 box holds 1 to 9 once, and each cage's digits add up to its sum without repeating; a clash or a cage total that cannot work is marked as soon as it is typed. Every puzzle is original, built on this page from its own solved grid by joining cages, and each join is kept only after a solver working within a set step limit proves the puzzle still has exactly one solution. The label on a puzzle counts its cages; it is not a tested difficulty, and there is no daily puzzle schedule.

Common questions

How do you play Killer Sudoku?: It is Sudoku with sums instead of given digits. Every row, column and 3 by 3 box holds the digits 1 to 9 once. The grid is also split into cages, drawn as dashed outlines with a small sum in the corner of each: the digits in a cage add up to that sum, and a cage never repeats a digit, even when its squares sit in different rows and columns. A two-square cage with sum 3 can only hold 1 and 2, in either order; 2 and 2 would add up to 4 but is never allowed. All the cage sums together always total 405, because each of the nine rows adds up to 45. The board here counts as solved only when every square is filled and every rule holds.
Does every Killer Sudoku here have exactly one solution?: Yes. Each puzzle starts from a complete, valid grid that a seeded search fills in. Every square begins as a cage of its own, squares left alone are joined to a neighbour first, and after that cages are joined two at a time in a seeded order, up to five squares each and never so that a cage would hold the same digit twice. After every join a solver narrows the digits each square can take and then searches on past the first solution for a second one. The join is kept only when it proves there is exactly one; a join it cannot settle within 3,000 steps is refused, not kept. Joining stops when the puzzle reaches a cage count its seed draws between 26 and 30, or when no join passes. If a build spends 60,000 steps first, leaves a square with no cage to join, or ends with more than 30 cages, the page opens one of 12 fixed seeds whose puzzles a separate brute-force solver has checked, and says why and which seed it opened.
What does the small number in a cage mean?: It is the cage's sum: the digits in the squares inside that dashed outline add up to it. The number sits in the cage's first square, reading left to right from the top row. The side pane lists every cage with its sum as text, and when you select a square it names the square's cage, how many squares it has, its sum and the digit sets that still fit it, given the digits already in its rows, columns and boxes. A screen reader hears the cage letter, its size and its sum for every square.
How do notes work?: Press Notes under the grid, or N on a keyboard, and the digits add or remove small pencil notes in the selected square instead of filling it. Press it again to go back to digits. Notes only go in empty squares, and typing a digit into a square clears its notes. Notes never count as filled squares or as a solution: a board full of notes is still an empty board. They are saved with your progress, and Undo takes them back like any other move.
What do Check, Reveal cell and Hint do?: Check compares every digit you typed with the puzzle's one solution and outlines the ones that differ until your next move. Reveal cell fills the selected square from the solution and locks it. Hint looks at the board in order: a digit twice in a row, column or box; a cage with a repeat or a total it can no longer reach; a digit that breaks no rule but is not part of the solution; then a square with only one digit left, with the reason each other digit is out, or a digit with only one place left in a row, column or box. If none of those settles anything, it names one answer in words. Hint never types a digit for you. Every check of your digits, every reveal and every hint marks the game assisted, the status shows how many of each you used, and Undo does not remove that mark. A clash you type yourself is marked red by the rules alone and is not an assist.
Can I print a Killer Sudoku puzzle?: Yes. Print puzzle prints the grid with its dashed cages and sums, headed with the seed and the cage count, with the rules underneath; tick the box under the tool to add the answer key on a second page. Print answer key prints the solved grid alone, with the same cages and sums. The grid prints 162 mm square. Copy puts the puzzle on the clipboard as text instead: a cage letter for every square with your digits, then every cage's sum.
What is the seed, and can I play the same puzzle again?: The seed is a whole number from 1 to 999999. The build draws its random numbers from a fixed formula seeded by it and counts the solver's steps rather than timing them, so the same seed makes the same puzzle on any device. The seed of the puzzle on the board is shown above the grid and in the Seed box. To open a puzzle again, type its seed and press Play seed. New puzzle picks a random seed.
Is my progress saved, and is there a timer?: Progress is saved in this browser only: the puzzle on the board, your digits and notes, revealed squares, how many checks, reveals and hints you used, and the timer, along with up to 9 earlier puzzles you left with a digit, a note or an assist used. A saved game reopens only when its seed rebuilds exactly the same cages and sums; an edited save is refused and the page says so. Undo reaches back through up to 400 moves made since the puzzle was opened in this visit. The timer is off until you switch it on; it then counts while the tab is visible and the puzzle is unsolved. Nothing is uploaded, and the Start over button at the top of the page forgets all of it. If the browser refuses storage, the side pane says the puzzle is not being saved, and it still plays.

Every row, column and 3 by 3 box holds 1 to 9 once, and each cage's digits add up to its sum without repeating; a clash or a cage total that cannot work is marked as soon as it is typed. Every puzzle is original, built on this page from its own solved grid by joining cages, and each join is kept only after a solver working within a set step limit proves the puzzle still has exactly one solution. The label on a puzzle counts its cages; it is not a tested difficulty, and there is no daily puzzle schedule.