💀 Killer Sudoku

🧮 What is Killer Sudoku?

If you have mastered the traditional game and are looking for a fresh puzzle, killer sudoku (also known as Sumdoku or Sumpon) is exactly what you need. It strips away the starting numbers from the board and replaces them with a brilliant mathematical twist. You can read more about how this specific variant was developed on the Killer Sudoku Wikipedia page.

The standard rules still apply—every row, column, and 3×3 block must contain the numbers 1 through 9 without repeating. However, the grid is now divided into dashed outlines called “Cages.”

• Each cage has a small number printed in its top-left corner.
• The numbers you place inside that cage must add up perfectly to that target sum.
• Crucial Rule: You cannot repeat a number within a single cage. For example, a 2-cell cage with a target sum of 4 must be solved with a 1 and a 3 (you cannot use a 2 and a 2).

🎯 How do you play Killer Sudoku?

If you are wondering how to play killer sudoku online, you will be happy to know it requires pure logic and only basic arithmetic. Here is how to conquer the board using our custom interface:

1. Find the “Givens”: Look for the easiest cages first. A 2-cell cage with a target of 3 can only ever be a 1 and a 2. A 2-cell cage with a target of 17 can only ever be an 8 and a 9.
2. Draft with Pencil Marks: Click the ✏️ Notes button to jot down possible combinations inside a cage without committing. When learning how to do a killer sudoku, mastering the notes tool is absolutely mandatory!
3. The “Rule of 45”: Remember that every row, column, and 3×3 block must always add up to exactly 45 (1+2+3+4+5+6+7+8+9 = 45). You can use this trick to mathematically deduce missing numbers that sit just outside of a cage block.
4. Watch Your Mistakes: If your numbers do not add up to the cage total, or if you repeat a number, our conflict scanner will immediately shake the cell and flash red.

⚙️ Built for an Expert Killer Sudoku

Because this variant requires intense focus and complex calculations, we integrated our most powerful platform engines directly into the game board to ensure a flawless experience:

🌍 Rank Up & Explore

Create your free account today to start tracking your completion times and earning XP for every sum-based grid you conquer. Want to challenge your friends? Hit the “Challenge” button after your game to send them a direct link to your exact board layout!

🎚️ The Four Killer Sudoku Difficulty Levels

Killer Sudoku here comes in four tiers — Easy, Hard, Harder and Hardest. What separates them is not the cages, which follow the same rules on every level, but how many ordinary digits are printed on the board before you start. Fewer given digits means more of the puzzle has to be worked out from cage sums alone.

• Easy — around 15 digits are already filled in. Those givens anchor the cages, so you can lean on normal Sudoku scanning while you learn how the sums behave. The right starting point if you have never played Killer before.
• Hard — around 9 givens. You will need to start reading the cages properly: which digit sets can reach a sum, and which cells those sets are forced into.
• Harder — only a handful of digits on the board. Most of the grid now has to come from arithmetic, and techniques such as the Rule of 45 stop being optional.
• Hardest — the board shows only the bare minimum number of digits needed to make the answer unique, typically just one or two. Almost everything is deduced from the cage totals. This is Killer Sudoku in its purest form.

Every layout, on every tier, is verified to have exactly one solution before you see it. There is never a point where two answers fit — if you are stuck, a logical step exists. And the harder the tier, the more XP a finished puzzle is worth on your profile.

🎮 Everything on the Killer Board

Killer Sudoku is free to play in your browser, with nothing to download and no account required — tap Play as Guest and a fresh puzzle is ready. Signing in is optional and only decides whether your times reach the leaderboards and whether your XP builds up across the site.

• Pencil notes. Mark the candidates a cage allows in each of its cells before committing. On Harder and Hardest this is how most people solve.
• Undo. Step back through your moves when a chain of cage arithmetic turns out to rest on a wrong assumption.
• Hints that reveal one verified digit when a board genuinely stalls, without handing you the rest of the grid.
• A live timer with pause — the clock stops and the board hides, so a break never costs you time.
• A mistake counter, so you can tell a careful slow solve from a careless one afterwards.
• Automatic saving of your grid, notes and elapsed time, so you can close the tab and pick the puzzle up later in the same browser.
• Shareable puzzle IDs. Every board has one. Send it to a friend, or paste an ID in to load a specific puzzle, and you both get the identical cage layout.
• Leaderboards for the fastest time on each tier, plus a global ranking by total XP.

🧮 Stuck on a Cage? Use the Calculator

When a cage has four or more cells, listing every digit set that reaches its sum in your head gets error-prone quickly. Our Killer Sudoku calculator lists every valid combination for any sum and cage size instantly, and lets you exclude digits already placed nearby. The same page carries a complete combinations chart covering all 502 possible cage combinations, with the single-solution cages marked.

Prefer pen and paper? The printable Killer Sudoku page generates PDF packs with answer keys, and every printed puzzle carries a QR code that opens the exact same board here if you want to finish it online.

❓ Killer Sudoku FAQs