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Building a puzzle with a single solution…
Killer learning studio
Turn cage totals into proven moves
Killer Sudoku becomes clear when every cage is read together with the row, column and box around it. Start with the information that is forced, keep combinations visible, then let a complete unit prove the next step.
01
Three signals, one proof
- 1A cage total tells you which digit combinations can exist.
- 2No digit may repeat inside a cage, so the combination remains precise.
- 3Rows, columns and boxes still total 45, linking local cages to the whole grid.
02
A cage total becomes a safe digit
A two-cell cage totalling 3 has only the digits 1 and 2. When the row already contains 1, the open cage cell is proven to be 2 — no guess is involved.
- 1Read the cage total and its number of cells.
- 2Remove combinations that repeat a digit or conflict with the grid.
- 3Place only the remaining digit the evidence allows.
03
Four levels, one connected method
Each difficulty strengthens one Killer skill. Pick the level that matches your current evidence, then move on when the next technique feels explainable rather than merely familiar.
Easy
- Best for
- Your first cages and calm, verifiable openings.
- Practice focus
- Extreme two- and three-cell combinations.
- Ready to progress when
- You can use cage digits with row and box constraints.
Medium
- Best for
- Solvers comfortable with basic cage combinations.
- Practice focus
- The Rule of 45 across one row, column or box.
- Ready to progress when
- A missing total becomes a useful candidate restriction.
Hard
- Best for
- Players keeping clean candidate combinations.
- Practice focus
- Innies and outies across a useful boundary.
- Ready to progress when
- You can explain an inside or outside remainder.
Expert
- Best for
- Experienced solvers who combine several constraints.
- Practice focus
- Multi-unit totals of 90 and 135.
- Ready to progress when
- You can choose a region with a provable multi-unit remainder.
04
Continue with real Killer tools
Read the underlying method, practise its exact technique, verify a position in the solver or print a fresh Killer grid — each route keeps the same cage-first logic intact.
Killer start
From cage to a safe move
Killer Sudoku becomes manageable when you read each cage as information, not arithmetic pressure. Build from forced combinations to the Rule of 45, then let the grid confirm every deduction.
Your first Killer routine
Read the cage
Start with its size and total. Extreme sums leave only a few possible digits.
Exclude repeats
A digit cannot occur twice in one cage. This turns a sum into a precise combination.
Use the 45 total
Every row, column and box totals 45. Subtract known cage sums to uncover what remains.
Learn Killer Sudoku step by step
Start with cage combinations, then build toward the Rule of 45, innies and outies, and precise cage exclusions.
Frequently asked questions
What is Killer Sudoku?
Killer Sudoku combines Sudoku with simple addition. The grid starts almost empty; instead of given digits you get dotted cages, each labelled with the total its digits must reach. Normal Sudoku rules still apply on top of that.
Can a digit repeat inside a cage?
No. Every digit inside one cage must be different, which is what makes the sums informative. A two-cell cage totalling 10 can be 1+9, 2+8, 3+7 or 4+6 — never 5+5.
How do I start a Killer Sudoku?
Look for the extreme sums first. A two-cell cage of 3 can only be 1+2, a three-cell cage of 6 only 1+2+3, and a four-cell cage of 30 only 6+7+8+9. Those forced cages give you the first real footholds.
Explore Cage combinationsWhat is the rule of 45?
Every row, column and box contains 1 to 9 exactly once, so its digits always add up to 45. If the cages inside a box account for 40, the remaining cell must be 5. This single observation solves a surprising number of positions.
Explore Rule of 45Is Killer Sudoku harder than normal Sudoku?
At first it feels harder because nothing is given. In practice the cage sums carry more information than a handful of starting digits, so once you know the standard combinations an easy Killer plays much like an easy classic puzzle.