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Killer Sudoku - Free Cage Sudoku Puzzle Game Online

Killer Sudoku combines the logic of Sudoku with the arithmetic of Kakuro. Fill the 9x9 grid so that every row, column, and 3x3 box contains 1-9, while also ensuring that cells within each cage add up to the displayed sum with no repeated digits. Three difficulty levels from generous givens to cages-only challenge, all generated instantly in your browser.

How to Play Killer Sudoku

Killer Sudoku combines the logic of classic Sudoku with arithmetic. Unlike classic Sudoku, the grid starts completely empty — there are no pre-filled numbers. Instead, cells are grouped into cages with target sums. Your job is to deduce every number using cage sums and Sudoku logic together.

If you know how to play Sudoku, you already know half the rules. Our three difficulty levels — Easy, Medium, and Hard — let you start gently and work your way up as you master the cage arithmetic.

Basics

  • 1

    Understand the Board

    The grid starts completely empty. Dashed borders group cells into cages. The small number in each cage's corner is the target sum — the numbers you place must add up to it.

    7
    12
    23
    22
    28
    15
    9
    6
    15
    4
    15
    22
    12
    28
    12
    20
    9
    11
    6
    10
    25
    15
    26
    25
    8
    12
    8

    Every cell is empty at the start — cage sums are your only clues.

  • 2

    Know the Rules

    Rule 1 — Standard Sudoku

    Each row, column, and 3x3 box must contain the numbers 1-9 exactly once — same as classic Sudoku.

    Each Row

    5
    3
    4
    6
    7
    8
    9
    1
    2

    Each Column

    5
    6
    1
    8
    4
    7
    9
    2
    3

    Each 3x3 Box

    5
    3
    4
    6
    7
    2
    1
    9
    8

    Rule 2 — Cage Sums (the Killer twist)

    The numbers in each cage must add up to the target sum, and no digit may repeat within a cage.

    10 3
    7

    3 + 7 = 10 ✓

    Digits are different

    10 5
    5

    5 + 5 = 10 ✗

    Digits repeat!

  • 3

    Learn Key Techniques

    Forced Combinations

    Some cage sums have only one possible combination of digits. These are your best starting points — you know exactly which numbers go in the cage, you just need to figure out their positions.

    2-cell cage

    3

    1 + 2

    2-cell cage

    4

    1 + 3

    2-cell cage

    16

    7 + 9

    2-cell cage

    17

    8 + 9

    3-cell cage

    6

    1 + 2 + 3

    3-cell cage

    7

    1 + 2 + 4

    3-cell cage

    23

    6 + 8 + 9

    3-cell cage

    24

    7 + 8 + 9

    The Rule of 45

    Every row, column, and 3x3 box always sums to exactly 45 (since 1+2+3+...+9 = 45). When all cages within a row are fully contained except one cell, you can calculate that cell directly.

    7 3
    4
    18 5
    6
    7
    12 1
    2
    9
    ?

    45 − 7 − 18 − 12 = 8

    Use Notes

    Notes mode is essential for Killer Sudoku. Mark all possible candidates in each cell, then eliminate options as you solve cages and apply Sudoku rules.

    Notes Mode

    1 3 5 7 9
    →

    Solved

    5
  • 4

    Complete the Puzzle

    Combine cage arithmetic with Sudoku elimination to fill every cell. Since you fill in every number yourself, the entire completed grid is your work!

    1
    2
    3
    4
    5
    6
    7
    8
    9
    4
    5
    6
    7
    8
    9
    1
    2
    3
    7
    8
    9
    1
    2
    3
    4
    5
    6
    2
    3
    1
    5
    6
    4
    8
    9
    7
    5
    6
    4
    8
    9
    7
    2
    3
    1
    8
    9
    7
    2
    3
    1
    5
    6
    4
    3
    1
    2
    6
    4
    5
    9
    7
    8
    6
    4
    5
    9
    7
    8
    3
    1
    2
    9
    7
    8
    3
    1
    2
    6
    4
    5

Tips & Strategies

Start with Forced Cages

Look for cages where only one combination of digits is possible. A 2-cell cage summing to 3 must be {1, 2} and a 3-cell cage summing to 24 must be {7, 8, 9}. These give you guaranteed digits to work with.

Apply the Rule of 45

Each row, column, and 3x3 box sums to 45. If a cage sticks out of a row by one cell, you can calculate the value of that cell by subtracting the other cages' sums from 45.

No Repeats in Cages

Even if a cage spans multiple rows or boxes, no digit can repeat within it. This extra constraint is a powerful elimination tool — use it alongside standard Sudoku logic.

Cross-Reference Everything

Use notes to mark all possible digits per cell, then cross-reference cage sums, row/column constraints, and box rules together. Each solved cell ripples through multiple constraints.

Controls

Mouse / Trackpad

Click on any empty cell to select it, then click a number (1-9) to fill it in. Click the pencil icon to toggle notes mode, and use Clear to remove a number.

Touch Screen

Tap any empty cell to select it, then tap a number to place it. Tap the pencil icon to enable notes mode for marking possible candidates in each cell.

Frequently Asked Questions

What is Killer Sudoku?
Killer Sudoku is a puzzle that combines standard Sudoku with Kakuro-style cage sum constraints. You fill a 9x9 grid so every row, column, and 3x3 box contains 1-9, while cells in dashed cages must add up to the given sum with no repeated digits within a cage.
How is Killer Sudoku different from regular Sudoku?
In regular Sudoku, some numbers are pre-filled as clues. In Killer Sudoku, cells are grouped into cages with a target sum instead. You must use arithmetic along with Sudoku logic to determine each cell's value. Harder difficulties may have very few or no pre-filled numbers.
Can digits repeat inside a cage in Killer Sudoku?
No. Each cage must contain unique digits that add up to the cage's target sum. This no-repeat rule within cages is a core constraint that provides additional solving information beyond standard Sudoku rules.
What do the difficulty levels mean in this Killer Sudoku game?
Easy puzzles provide around 20 pre-filled givens alongside cages, making them approachable for beginners. Medium puzzles have around 10 givens, requiring more cage arithmetic. Hard puzzles rely on cages only with no givens, demanding advanced logic and combination analysis.
What strategies help solve Killer Sudoku puzzles?
Start with cages that have only one possible combination (e.g., a 2-cell cage summing to 3 must be 1+2). Use the notes feature to track candidates. Cross-reference cage sums with row, column, and box constraints. Look for "naked singles" where only one digit fits, and eliminate impossibilities systematically.
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