chordup › Killer Sudoku AI Coach
Killer Sudoku AI Coach
Killer Sudoku AI Coach is a free app that teaches killer sudoku by showing how to think your way to the next number. It explains killer-specific reasoning — cage combinations, the Rule of 45, innies and outies — by highlighting the board step by step.
Play in your browser Learn the techniques
What is killer sudoku?
Killer sudoku is sudoku with cages: dotted outlines with a total in the corner. As in sudoku, every row, column, and box holds 1 to 9 once each. On top of that, the numbers in each cage add up to its total, and no number repeats inside a cage.
Most puzzles start with few or no numbers, so the cage totals are your clues. It takes a different way of thinking from regular sudoku, which is why many people get stuck at first.
Three-step hints
Like Sudoku AI Coach, hints come in three steps: where to look, how to think, and the answer and why.
- Where to look — highlights the cage, row, column, or box to focus on
- How to think — explains the reasoning, such as a cage combination or the Rule of 45
- The answer and why — shows the number and the cells that prove it
Killer-specific techniques
- Cage combinations — narrow down a cage's digits from its total and size
- The Rule of 45 — every row, column, and box adds up to 45, so you can work out the cells that stick in or out
- Cage pointing, the Rule of 45 across several lines, and innie–outie differences
Together with standard sudoku techniques (pairs, X-Wing, and more), that's 26 techniques you can learn in order.
Hints you can trust
Moves are found by a solver that uses human techniques, and every puzzle is generated and checked by it: each has exactly one solution and needs no guessing. If you're still stuck, you can ask the owl AI coach.
What's inside
- Six difficulties from Beginner to Master
- Daily puzzles and free play
- Technique guides, practice puzzles, and a cage combinations chart
- Records and rankings
- 71 languages
Price and ads
It's free to play. It may show ads to cover running costs.
Techniques you can learn (easiest first)
Each technique has its own guide with a worked example, cages included.
- Hidden Single (only one place for it)
- Naked Single (only one number fits)
- Cage Combinations
- Rule of 45 (Innies & Outies)
- Cage Pointing
- Pointing Pair (lined up inside a box)
- Box/Line Reduction (a line decides the box)
- Naked Pair
- Hidden Pair
- Naked Triple
- Hidden Triple
- Rule of 45 (Several Rows or Columns)
- X-Wing
- Swordfish
- XY-Wing
- XYZ-Wing
- Innie-Outie Difference
- Skyscraper
- 2-String Kite
- Unique Rectangle
- Empty Rectangle
- W-Wing
- Naked Quad
- Hidden Quad
- Finned X-Wing
- Jellyfish
Read on the site
- Killer sudoku rules: how to play
- How to solve killer sudoku, step by step
- Cage combinations chart (all 502)
FAQ
- Do I need to be good at math?
- No — only single-digit addition and subtraction. The combinations chart is always there to check, and the common ones stick after a few puzzles.
- Can I play if I've never done regular sudoku?
- Yes. The app asks if you're new to killer sudoku and, if so, walks you through the rules first.
- Can I play without installing anything?
- Yes. The browser version has the same puzzles and hints.
- Which languages does it support?
- 71 languages, including English and Japanese.