Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
What is Jigsaw Sudoku?
Jigsaw Sudoku is classic Sudoku with the nine 3×3 boxes cut into nine irregular shapes. Everything else is the same. Fill the grid so that:
- every row holds 1 to 9 exactly once;
- every column holds 1 to 9 exactly once;
- every coloured region holds 1 to 9 exactly once, whatever shape it is.
It is sold under four names — jigsaw sudoku, irregular sudoku, nonomino sudoku and squiggly sudoku — and they are all the same puzzle. A nonomino is simply a nine-cell shape, which is what each region is: nine cells joined edge to edge, never a 3×3 square.
Sudoku logic works on houses: groups of nine cells that must each hold 1 to 9 once. A jigsaw grid has the same 27 houses as classic Sudoku — nine rows, nine columns, nine regions — so every technique you already know still applies. Only the shape of nine of them has changed, and with it where they reach.
Where do you start on an irregular grid?
Pick a digit and ask where it can still go inside one region. That is the jigsaw version of cross-hatching, and it is the move that pays, because a region reaches further than a box ever does.
The shape is doing the work. A 3×3 box touches exactly three rows and three columns. Across 1,200 boards from this page, about a third of all regions reach five rows or more, and the longest we have seen stretch across all nine. A region that spans six rows is cut by six rows’ worth of digits, so it is pinned down faster than a box would be — which is why scanning regions first, before filling in pencil marks, finds more than a row scan does.
What is a region-line lock?
This is the one technique that belongs to jigsaw. If a digit’s remaining homes inside a region all sit in the same row, the region must use that row for it — so the rest of the row cannot have it.
It works the other way round too. If a row’s last homes for a digit all fall inside one region, that region spends its copy of the digit on the row, and the rest of the region loses it. Both directions are locked candidates, the same technique that gives you pointing pairs and box-line reduction in classic Sudoku; a bent region just offers more of them, because its cells fall across more rows and columns to begin with.
What do the four levels actually need?
We ran 300 fresh boards per level through a solver that knows one technique at a time, then took each technique away to see which boards stopped. This is what our generator deals:
| Level | Given digits | Singles alone finish it | Needs a region-line lock | Needs a pair, triple or X-Wing | Beyond our solver |
|---|---|---|---|---|---|
| Easy | 40 | 100% | 0% | 0% | 0% |
| Medium | 33 | 99% | 1% | 0% | 0% |
| Hard | 28 | 83% | 12% | 2% | 3% |
| Expert | 25 | 51% | 30% | 10% | 8% |
300 boards per level from this page’s generator, fixed random seed, rounded. Each board is filed under the hardest step it needed. “Beyond our solver” boards still have exactly one answer; they need longer chains than our solver’s techniques cover.
Easy and Medium are not harder than classic Sudoku — they are ordinary Sudoku with odd-looking boxes. Naked and hidden singles finish every Easy board and all but one Medium board in a hundred. The variant only bites from Hard: at Expert, half the boards need more than singles, and if we switch region-line locks off, 28 of 300 Expert boards cannot be finished at all. Pairs, triples and the X-Wing show up on a tenth of them.
The generator takes a finished grid and removes digits one at a time, keeping a removal only while the puzzle still has exactly one answer — and it is honest about a check it could not finish, rather than dealing the board anyway. As a second opinion we re-solved 1,200 fresh boards and all 164 daily puzzles with a separate solver written for the purpose: every one had exactly one answer. A board takes about 15 milliseconds to build, 40 at Expert, so the puzzle is there before the page has finished loading.
Is Jigsaw Sudoku harder than classic Sudoku?
At the level you are likely to start on, no. The numbers above are the honest answer: our Easy and Medium boards want nothing but singles, and Easy starts you with 40 of the 81 digits already filled in. What changes is not the difficulty but the reading. Your eyes know where a 3×3 box ends without looking; they do not know where a region ends, and that is the whole adjustment.
At Hard and Expert it does get harder than the same clue count would be in classic Sudoku, for a structural reason: a bent region shares cells with more rows and columns than a box does, so each region gives its neighbours more to work with, and a generator can take more digits away before the answer stops being unique. Our Expert boards keep 25 given digits and still have exactly one answer.
What goes wrong on a jigsaw grid
- Losing the border. Nearly every mistake is a digit placed by the shape you assumed rather than the one drawn. Follow the colour, not the neighbourhood.
- Solving it as if the boxes were still there. If a move would work on a 3×3 grid, the regions are not earning their place — and on Expert, that is where half the board is hiding.
- Pencilling everything in first. On an irregular grid a full set of notes hides the shapes. Scan the regions while the grid is still readable, then mark up what is left.
What do the buttons do?
Select a cell, then a digit from 1 to 9; the page opens on Medium. Under the grid:
- Notes turns pencil marks on and off. A correct digit clears itself from the notes of its row, its column and the rest of its region; a wrong one leaves your notes alone.
- Erase clears the selected cell, and pressing the same digit twice does the same.
- Undo takes back the last change to a cell, though not the notes a correct digit cleared elsewhere, and not the Mistakes count.
- Hint fills one empty cell with its answer, picked at random rather than the cell you could work out next.
- Solve asks first, then fills the grid and stops the timer.
- New Game deals another board at the level you are on; the level buttons deal one at theirs.
Digits 1–9, the arrow keys, Backspace or Delete and Ctrl+Z all work from a keyboard. The board is saved in this browser after every move, timer included, so it is waiting when you come back. Each region is tinted so that no two touching regions share a colour, and selecting a cell lights up the rest of its region along with its row and column — the fastest way to see a shape you are about to misread.
Daily, printable and solvable elsewhere
The daily Jigsaw Sudoku gives everyone the same board each day, from the same generator, and the whole archive is there to play. On paper, each level is a free PDF with answers: Easy, Medium, Hard and Expert, listed on the printable Jigsaw Sudoku page. Stuck on a puzzle from a book, or want to know whether it has one answer at all? Draw it into the Jigsaw Sudoku solver, regions and all.
If you like what the regions do here, the same trick of adding one more house is what drives X-Sudoku, where the two diagonals join in, and Windoku, which hides four extra boxes inside the grid. Killer Sudoku goes the other way and replaces the given digits with sums.