Killer learning library
Killer Sudoku techniques
Learn the twelve essential Killer Sudoku techniques in a clear order. Every lesson combines a real cage diagram, a verifiable deduction and a focused practice puzzle.
12
12 techniques
12
Interactive examples
12
Practice puzzles
Learning path
From cage sums to advanced regions
Start with forced cage combinations, then use the Rule of 45 and finish with advanced incomplete sums. Each card opens one complete, explainable next step.
01
Cage arithmetic
Use cage size and sum to find the digit sets that can still fit.
Beginner
Cage combinations
A cage sum plus its size limits which digits can appear. A two-cell cage summing to 3 can only be 1 and 2 — no other pair works.
Open lessonBeginner
Last cell in a cage
When every cell of a cage but one is filled, the missing digit is simply the sum minus what is already there.
Open lessonBeginner
Killer Naked Single
A cell still has several Classic candidates, but its cage combinations leave exactly one of them. That surviving digit is a safe Naked Single.
Open lesson
02
Killer rules
Apply the additional Killer restriction that each cage contains distinct digits.
03
Rule of 45
Turn the fixed totals 45, 90 and 135 into visible, checkable deductions.
Intermediate
Rule of 45
Every row, column and box holds the digits 1 to 9 exactly once, so its digits always add to 45. Cages that stick out reveal the difference.
Open lessonIntermediate
Innies and outies
Cells reaching into a unit from outside are innies; cells reaching out are outies. The rule of 45 gives their total.
Open lessonAdvanced
Rule of 45 across several units
Two rows add to 90, three boxes to 135. Larger regions isolate cells that a single unit cannot.
Open lessonAdvanced
Incomplete sums
Use the known total of a complete 45-, 90- or 135-region to constrain several boundary cells.
Open lesson
04
Elimination
Remove candidates that cannot survive the remaining cage combinations and Sudoku rules.
Intermediate
Cage elimination
If a digit appears in none of a cage's possible combinations, it can be removed from every cell of that cage.
Open lessonAdvanced
Cage-Line Reduction
When a compulsory cage digit can occupy only cells on one row, column or box, remove it from the rest of that unit.
Open lessonAdvanced
Killer pairs
Two cells in one cage that share the same two candidates lock those digits — like a naked pair, but driven by the cage sum.
Open lessonAdvanced
Cage subsets (Rule of K)
Cage arithmetic restricts a triple or quad to exactly K digits; those digits are then locked in one row, column or box.
Open lesson
The other track
Looking for Classic Sudoku techniques?
Classic and Killer share the same proof-first hint quality, but their logic differs. Explore the separate Classic library for singles, subsets, fish, wings and chains.