Samurai Sudoku
Five overlapping 9×9 grids. Shared boxes that connect them all. Pick your difficulty and start solving.
Samurai Sudoku
160–200 givens. Grids mostly solvable on their own.
Standard play. Timer runs. Hints available.
What is samurai sudoku?
Samurai sudoku is five standard sudoku grids arranged in an X shape on a 21×21 board. One grid sits in each corner and one in the center. The corners overlap with the center at four 3×3 boxes, so a digit placed in a shared box has to satisfy constraints from two grids at once. Some people call this format 5 grid sudoku, overlapping sudoku, or multi sudoku. In Japan it's sometimes listed as sudoku samurai.
The puzzle was popularized by The Times of London in 2005, though overlapping grid formats had appeared in Japanese puzzle magazines before that. It caught on because it takes the familiar 9×9 rules everyone already knows and adds a new dimension: you can't solve any single grid in isolation. The shared boxes link everything together.
The total grid has 405 cells (five grids of 81, minus the 36 cells in four shared boxes that get counted once instead of twice). On an easy puzzle you might get 180 givens, leaving around 225 cells to fill. On an Einstein puzzle, you get fewer than 50 givens for those same 405 cells.
Samurai vs. standard sudoku
A regular sudoku is 81 cells, one grid, one set of constraints. A samurai sudoku is about five times larger and takes proportionally longer, but the extra shared-box constraints give you more information to work with, not less. An easy samurai puzzle can be simpler to reason about than a hard standard 9×9.
The real difference is the workflow. In a regular sudoku, you can focus on one area of the grid and ignore the rest until you need it. In samurai sudoku, you bounce between grids constantly. Solving a cell in the center grid might give you a digit in the top-left grid through the shared box, and that digit might cascade into filling several more cells in the corner. Getting comfortable with this back-and-forth is the main skill jump.
Compared to killer sudoku (which adds cage-sum constraints) or KenKen (arithmetic cages on smaller grids), samurai sudoku keeps the basic 1-9 rule set and changes the geometry instead. If you like standard sudoku and want something bigger without learning new rules, samurai is a natural step up.
How to play
Tap a cell to select it, then tap a number. The standard sudoku rule applies inside each of the five grids: every row, column, and 3×3 box must contain 1 through 9 exactly once. Shared cells are tinted so you can see which boxes belong to two grids.
On desktop, arrow keys move between cells across all five grids, skipping the dead zones (the four rectangular gaps where no grid exists). On mobile, you can switch to Focus Mode, which shows one sub-grid at a time with five thumbnail buttons to jump between them. Shared cells stay synchronized whichever view you use.
Want the full rundown? Read the rules.
Play modes
Classic
Timer runs up. Up to 3 hints. Undo anytime. The standard way to play.
Timed Trial
Beat the clock. 12 to 30 minutes depending on difficulty.
Challenge
No hints, no undo, no check. Every move is permanent.
How to solve samurai sudoku
Technique by technique, from your first overlapping puzzle to the hardest Einstein grids.
Start from the center
The center grid is the most constrained because it shares a 3×3 box with every corner grid. Any digit you place there has the best odds of cascading outward. Most experienced solvers scan the center first, fill what they can, then move to whichever corner has the most information.
If you're new to samurai and feel overwhelmed by the 21×21 board, Focus Mode helps. Switch to the center grid, treat it like a regular 9×9, and work from there.
Think in shared boxes
Shared boxes are where samurai sudoku gets interesting. When a box belongs to two grids, every cell in that box has double the constraints. That means the candidates for those cells are the intersection of what both parent grids allow.
In practice, this often means shared-box cells have fewer candidates than you'd expect. If you place a digit that leaves only one candidate in a shared cell from the center grid's perspective, but the corner grid already blocked that candidate, something is wrong. Checking shared-box consistency is how you catch errors early.
Bounce between grids
Getting stuck on one grid is normal. When it happens, switch to a grid that shares a box with the stuck one. Placing digits there often unlocks cells back in the original grid through the shared box. This back-and-forth is the core rhythm of samurai solving.
Beginners tend to try finishing one grid before moving on. That rarely works except on easy puzzles. Even at medium difficulty, you'll need information from at least two grids to make progress on any one of them.
Pencil marks and cross-grid candidates
With 405 cells, pencil marks aren't optional past easy difficulty. The auto-candidates mode fills them in for you, and it accounts for cross-grid constraints in shared boxes. If a candidate appears in the auto-fill, it's legal in both parent grids.
Manually maintaining candidates across five grids is tedious and error-prone. Use the auto mode while learning, and switch to manual once you want the extra challenge of tracking candidates yourself.
Cross-grid deduction chains
On hard and expert puzzles, you'll hit situations where no single grid has enough information to solve a cell. The answer depends on a chain of deductions that crosses two or more grids through shared boxes.
Example: eliminating a candidate in the center grid's top-left box forces a naked single in the top-left grid, which completes a row in that grid, which eliminates a candidate in the top-left grid's bottom-right box (shared with center), giving you a hidden single back in the center. These chains are why expert samurai takes longer than five separate expert sudoku puzzles.
Einstein difficulty
Einstein samurai puzzles have fewer than 50 givens across all five grids and are certified solvable by logic alone. No guessing, no bifurcation, just constraint propagation and deduction.
At this level, you need everything: naked and hidden singles, pairs and triples, pointing pairs, box/line reduction, and extensive cross-grid chains. The puzzles often start with almost nothing solvable in any individual grid. Your first placements come entirely from shared-box intersections.
Difficulty levels
Sudoku variants
Standard Sudoku
The original 9×9 format. Start here if you haven't played sudoku before.
Killer Sudoku
No given digits. Cage sums replace givens. Arithmetic meets constraint logic.
KenKen
Arithmetic cages on a Latin square grid. Four operations.
Futoshiki
Inequality signs between cells. Logic on a smaller grid.