Jigsaw Sudoku (also called Irregular Sudoku) keeps the Classic rule for rows and columns and swaps the 3×3 boxes for nine irregular regions of nine cells. The regions change from puzzle to puzzle, so the first job is reading the shapes.
The rules
Fill the 9×9 grid so that every row and every column holds the digits 1 to 9 exactly once, as in Classic Sudoku.
Instead of 3×3 boxes, the grid is cut into nine regions with thick borders. Each region has nine connected cells and must hold 1 to 9 exactly once. The 3×3 blocks mean nothing here: a digit can repeat inside one.
Regions are numbered in reading order, so region 1 is the one holding the top-left cell. Next Step uses those numbers and lights the region it means.
What the regions change
A box always meets a row in exactly three cells. A region can meet a row or column in anything from one cell to five on this site’s layouts. That changes where digits can lock, and it is where most of Jigsaw’s new ideas come from.
Every layout here is symmetric: turn the grid half a turn and the regions land on each other, and so do the clues. There are 196 layouts, shared by the 4,000 puzzles.
In Classic every cell sees exactly 20 others. In Jigsaw it depends on how a cell’s region overlaps its row and column: on these layouts, anywhere from 17 to 23. The familiar Classic techniques all still work once you can see the shapes.
How to solve it
Start with the regions, not the rows. Odd shapes hide singles: a region that snakes across several rows can have only one place left for a digit that the rows around it already hold.
Look where a region and a row overlap by several cells. If a region’s only places for a digit all sit in one row, that row cannot have the digit anywhere else. It works the other way too, from a row into a region.
Keep the 3×3 blocks out of your head. Scanning a 3×3 block for a missing digit is a Classic habit, and in Jigsaw it leads nowhere.
Worked examples
Three positions from real puzzles on this site, walked through by the same Next Step teacher you get in a game. Step through each one.
A hidden single in a region
Look at region 4. The digit 2 must go somewhere in this region. Where can it go?
A region locks a digit into a row
In region 2, find every cell that can still take 9.
A row locks a digit into a region
In row 1, find every cell that can still take 9.
The four levels
Jigsaw levels are graded on the same scale as Classic, so a Medium Jigsaw needs the same techniques as a Medium Classic puzzle. Every puzzle is solvable by logic alone, which is why there is no Diabolical level.
Classic techniques, with regions in place of boxes
Every Classic technique still works; where a lesson says "box", read "region". These lessons teach them on Classic boards:
Frequently Asked Questions
Is Jigsaw Sudoku harder than Classic?
Not by its levels: they use the same technique scale as Classic. The shapes do make scanning slower at first, until you stop looking for 3×3 boxes.
Do the 3×3 boxes still count?
No. Only rows, columns and the thick-bordered regions have a rule. A 3×3 block may hold the same digit twice.
Are the regions always the same shape?
No. There are 196 layouts here, shared by the 4,000 puzzles, all symmetric under a half turn, each with nine connected regions of nine cells.
How are the regions numbered?
In reading order: region 1 holds the top-left cell, and the numbers continue left to right, top to bottom, by where each region first appears.
Why is there no Diabolical level?
Every Jigsaw puzzle on this site can be solved by logic, up to Extreme techniques. Diabolical puzzles need trial and error, so they are left out.
What is it also called?
Irregular Sudoku, and sometimes Nonomino Sudoku, after the nine-cell shapes.
Which tools can I use?
All of them: pencil marks in corner or centre notation, candidates, Auto Check, Check Cell and Check Puzzle, and Next Step, which names the region whenever it is the reason for a move.
Try one now. Easy is a good place to start.