Sudoku with cage sums. Four difficulty levels and a daily puzzle, every one with a single proven answer, notes, a cage-combination helper and a number pad that fits a phone.
Killer sudoku is a sudoku variant in which the 9 by 9 grid is cut into dotted cages, each showing a sum in its top left corner, and you fill every cell with 1 to 9 so that no digit repeats in any row, column, 3 by 3 box or cage, and the digits of each cage add up to its sum. A cage of two cells with the sum 3 can only hold 1 and 2. A cage of three cells with the sum 24 must be 7, 8 and 9. There are no starting digits except for cages of one cell, which this page fills in for you because their sum is the digit. Every puzzle has exactly one answer. Easy, Medium and Hard puzzles can be finished by logic alone; Expert puzzles may need longer chains or trial and error.
The first skill in killer sudoku is knowing which sets of digits can make a sum. Two cells adding to 17 must be 8 and 9. Three cells adding to 15 have 8 possible sets, such as 1 5 9 or 4 5 6. Four cells adding to 10 can only be 1 2 3 4. The line under the board lists the possible sets for the cage you have selected, and it narrows as you place digits in that cage. The second skill is the 45 rule: every row, column and box adds up to 45, so if cages fill a unit except for one cell, that cell equals 45 minus the cages. If a cage sticks out of a unit by one cell, that outside cell is the cage sum minus the part inside. Looking for these single cells is how most Medium and Hard puzzles begin.
Each puzzle starts from a random complete sudoku grid, which is cut into random connected cages of 1 to 5 cells with no repeated digit. A solver then counts the solutions. If there is a second one, a cage is split so that the second solution breaks, and the count is repeated until exactly one solution is left. The result is stored as cage shapes and sums only, and your browser re-solves it when you open it, so a puzzle with more than one answer would never load. Difficulty is measured by logic, not by guesswork: a second solver that uses only human techniques solves each puzzle, and the hardest technique it needs sets the level. Easy needs only singles and cage combinations. Medium adds the 45 rule for one cell, locked candidates and pairs. Hard adds the 45 rule over several cells or units, hidden pairs and naked triples. Expert puzzles are the ones that solver cannot finish, so they need longer chains or trial and error. On average Easy has about 38 cages and Expert about 25. There are 365 puzzles at each level, shown in 8 orientations, and the daily puzzle picks one by the date.
Tap a cell to select it, then tap a number on the pad. The Notes button switches the pad to pencil marks, which sit in a small 3 by 3 layout inside the cell. By default, placing a digit removes that digit from the notes of its row, column, box and cage; turn that off in the ⋯ menu if you prefer to manage notes yourself. Show conflicts outlines repeated digits and cages that can no longer reach their sum. Undo and Redo step through your last 400 changes. On a keyboard, use the arrow keys to move, 1 to 9 to fill, P to toggle notes, Backspace to erase, U or Ctrl+Z to undo, Ctrl+Y to redo, and H for a hint. Hint fills the selected cell with the right digit, and Check for mistakes outlines every wrong digit. Both mark the game as helped, so it does not set your best time.
The Daily puzzle uses the date on your device, so everyone with the same date gets the same puzzle at the level they choose. Each level has its own daily. Your digits, notes and time are saved in this browser for each puzzle, and the last 12 puzzles are kept. Win streaks, best times and the daily streak are kept per level, in this browser only. The puzzles are built into the page, so no puzzle is requested while you play and nothing you enter is uploaded. The page sends anonymous Google Analytics events when it opens, when you make your first move and when you finish a puzzle. They never include your board, digits or time.
Fill the 9 by 9 grid with 1 to 9 so no digit repeats in a row, column, 3 by 3 box or dotted cage, and each cage adds up to the small number in its corner. A cage of 2 cells with the sum 4 must be 1 and 3.
Every row, column and box holds 1 to 9 once, so it adds up to 45. If the cages inside a row add to 38 and one cell is left over, that cell is 7. It also works in reverse: a cage that sticks out of a unit by one cell gives that cell's value.
Yes. The generator counts solutions and splits cages until exactly one is left, and the page checks again when it loads a puzzle. A solver that uses only human techniques grades each one, and 1,460 stored puzzles are tested for a single answer.
Yes. Select any cell and the line under the board lists every set of digits for its cage, for example 4 cells adding to 10 shows only 1234. It drops the sets that clash with digits you have already placed in that cage.
Easy needs only single digits and cage combinations, with about 38 cages. Medium adds the 45 rule for one cell and pairs. Hard needs the 45 rule across several cells or units. Expert has about 25 cages and goes beyond those techniques.
Press Daily in the ⋯ menu for a puzzle seeded by your local date, such as 2026-10-25. Hint and Check mark the game as helped. It still counts as a win and keeps your streak, but it does not set your best time.