Sudoku Written and built by Brian Hamilton. Reviewed by Karan Hamilton.
Brian handles the technical puzzle logic, while Karan checks the page for clarity, usability, and player experience.
Puzzle tools are tested in the browser against Sudoku rules, example grids, and common player workflows. See how we make and test puzzles, our editorial standards, or report a problem.
Jigsaw Sudoku Solver: solve irregular Sudoku online
Our free Jigsaw Sudoku Solver helps you solve jigsaw sudoku puzzles — 9x9 irregular grids where the normal square boxes are replaced by nine jigsaw-shaped regions. Draw each region exactly as it appears in your puzzle, enter the printed givens, and solve the grid using row, column, and custom region rules. The tool is designed for players who need to solve or check a Jigsaw Sudoku answer without translating irregular regions into a confusing text code.
Jigsaw Sudoku keeps the familiar goal of placing the digits 1 to 9 in every row and every column. The difference is the box rule. Instead of nine fixed 3x3 boxes, the grid is divided into nine irregular regions, and each region must also contain the digits 1 to 9 exactly once. Those regions may bend, stretch, wrap around corners, or touch each other in shapes that look nothing like standard Sudoku boxes. Because the regions define a core part of the logic, our classic Sudoku solver cannot solve a Jigsaw Sudoku at all — it has no way to be told where the boxes are.
This page combines a visual region editor with a Sudoku solving engine. You can trace the regions, save each 9-cell area, switch to number entry, add the givens, solve, and export the puzzle state. The solver also checks common setup mistakes, including repeated digits, missing cells, regions that are too small or too large, and layouts where not all 81 cells belong to exactly one region.
What is Jigsaw Sudoku?
Jigsaw Sudoku is also called Irregular Sudoku, Nonomino Sudoku, Geometry Sudoku, or Region Sudoku. The word nonomino simply means a shape made from nine connected cells. In a standard 9x9 Jigsaw Sudoku, there are nine nonomino regions. Each one acts like a Sudoku box, even though it may be shaped like a staircase, hook, snake, island, or blocky puzzle piece.
The solving rules are simple to state: every row must contain 1 to 9, every column must contain 1 to 9, and every jigsaw region must contain 1 to 9. No digit can repeat inside any of those units. The challenge is that the irregular regions create different intersections from standard Sudoku. A digit might be forced because of an unusual region boundary, or a candidate might be removed because two cells share a region even though they are far apart visually.
Good Jigsaw Sudoku puzzles feel familiar and surprising at the same time. You still use scanning, candidates, singles, pairs, and eliminations, but the shape of the regions changes where those techniques apply. That is why a dedicated irregular Sudoku solver is useful: it lets you define the actual regions rather than pretending the puzzle has normal boxes.
How much the regions are actually doing
The paragraph above says a normal Sudoku solver cannot reliably solve a Jigsaw Sudoku. That is easy to assert, so here it is measured. We generated a grid, then counted its solutions twice — once with the nine irregular regions, once reading the very same digits as an ordinary Sudoku.
That is worth holding on to when a puzzle will not solve. The region map carries as much of the puzzle as the digits do, and it is the half people transcribe carelessly.
How to use the Jigsaw Sudoku solver
- Choose Regions mode before entering numbers. Drag across connected cells to mark one jigsaw region.
- Save the region only when it contains exactly nine cells. Repeat until all nine regions are defined.
- Compare the colored region borders with your source puzzle. Delete and redraw any shape that does not match.
- Switch to Numbers mode and enter the givens printed in the puzzle.
- Click Solve to complete the grid and check whether the puzzle appears to have one solution.
- Use Import and Export if you want to save the region layout, share the puzzle, or return to the same puzzle later.
The best workflow is to define all regions first, then add digits. If the layout is wrong, even one misplaced cell can change the entire puzzle. When tracing from a book, screenshot, or PDF, work region by region and check the borders after every save. A valid 9x9 Jigsaw Sudoku must cover all 81 cells with nine separate 9-cell regions; no cell should be outside a region and no cell should be counted twice.
After the region map is correct, number entry is straightforward. Select a cell and use the number buttons or keyboard to enter the clues. Only enter the givens from the original puzzle before solving. If you enter a guess as if it were a clue, the solver may report no solution even though the original puzzle is valid.
Drawing irregular regions accurately
The region editor is the most important part of a Jigsaw Sudoku solver. Text-based region codes can be compact, but they are also easy to mistype. A single wrong character can move a cell into the wrong region, creating duplicate digits or an impossible puzzle. The visual editor lets you draw the layout the same way you see it on the page.
Each region must be connected, and the editor enforces it rather than trusting you: when you release a selection it walks the shape from one cell to the next through shared edges, and refuses to save with "Region cells must touch orthogonally" if any cell cannot be reached that way. Diagonal contact does not count — two cells meeting only at a corner are, as far as the check is concerned, not touching. If a source puzzle looks like it has a disconnected region, zoom in and re-read the outline; it is nearly always a faint border or a low-resolution scan rather than an exotic ruleset.
Use the colors as a final audit. Once all nine regions are saved, scan each row of the grid and confirm that every cell has a region color. Then scan the source puzzle and compare the thick boundaries. If a region bends around another region, verify both sides of the bend. These small checks save time because a wrong layout can produce a plausible but incorrect completed grid.
What one misplaced cell actually costs
The warning above — that a single misplaced cell can change the whole puzzle — sounds like ordinary caution. It is not. Here is the same grid with two cells traded between neighbouring regions.
This is why "no solution" so rarely means the published puzzle was broken. A region border traced one cell wide of the mark produces a grid that passes every check and cannot be solved, and the error is in the part of the screen you stopped looking at once the numbers went in.
What the solver checks before solving
Before solving, the tool checks the structural rules that make a Jigsaw Sudoku valid. It confirms that nine regions exist, that each region contains nine cells, and that every grid cell belongs to exactly one region. It also checks the givens for repeated digits in rows, columns, and regions. These validations catch most input errors before the solver spends time searching for an answer.
When a puzzle has no solution, the cause is often an input problem rather than a flawed published puzzle. Check whether a digit was copied into the wrong row, whether a region includes eight or ten cells, or whether two adjacent region shapes were accidentally swapped. If the solver reports multiple solutions, the puzzle may be underconstrained, or a given may have been omitted during entry.
The uniqueness check is useful for puzzle makers as well as solvers. If you are designing an irregular Sudoku, a beautiful region pattern is not enough. The clue set must lead to one fair solution. A solver that can report multiple solutions helps you tune the puzzle before printing, sharing, or publishing it.
Jigsaw Sudoku solving strategies
Start with the same basics you would use in classic Sudoku. Look for rows, columns, and regions that already contain many digits. If a cell has only one possible digit after checking its row, column, and region, place it. If a digit can appear in only one cell within a row, column, or region, that hidden single is also safe.
Then pay close attention to region-row and region-column interactions. In standard Sudoku, these are often called box-line reductions. In Jigsaw Sudoku the same idea applies, but the shapes are irregular. If all possible positions for a digit inside one region lie in the same row, that digit can be removed from the rest of that row outside the region. If all possible positions lie in the same column, remove it from the rest of that column. Irregular shapes often create strong versions of this pattern.
Pairs and triples work too. If two cells in a region can contain only the same two digits, those digits can be removed from every other cell in that region. If the same pair lies in one row or column, it can also affect the row or column. The unusual shape of a jigsaw region can make these patterns easier to miss, so it helps to scan each region as its own unit rather than only reading the grid row by row.
Advanced solvers can use X-Wing, Swordfish, colouring, and chain logic in Jigsaw Sudoku, but the region layout often provides enough extra structure for many puzzles. Before using advanced techniques, recheck the region boundaries and candidate notes. A wrong candidate caused by a missed region conflict can make the puzzle look harder than it really is.
Importing, exporting, and saving puzzle layouts
Jigsaw Sudoku has more information than a normal Sudoku grid because the region layout must be saved alongside the givens. That is why export is useful. It can preserve both the digits and the custom region map, making it easier to continue later or share the exact puzzle state with someone else.
If you import a saved puzzle, review the region colors before solving. The givens may look correct, but the region map is just as important as the numbers. If you paste only a givens string without region data, you still need to draw or import the irregular regions before the solver can apply the correct rules.
Exporting is also handy for teachers and puzzle creators. You can build a region layout once, test several clue sets, and keep a record of which versions were unique. For classroom use, export the puzzle before revealing the answer so you can return to the original state later.
Common mistakes with irregular Sudoku
The most common mistake is drawing a region with the wrong number of cells. Every region must contain exactly nine cells. The second most common issue is a copied digit in the wrong cell, especially when the source puzzle has heavy borders or small print. A third issue is assuming that jigsaw regions work like normal boxes. They do not; the only boxes that matter are the custom shapes you draw.
If the solver cannot solve the puzzle, do not immediately assume the source is broken. Compare the givens row by row, then compare the region borders. Look for a repeated digit in a single region. Look for one uncolored cell. Look for two neighboring cells that should belong to different regions but were dragged together. These small entry errors explain most failed irregular Sudoku solves.
If the solution looks wrong, check whether you entered extra working notes as givens. A solver treats every entered digit as fixed. Clearing guesses before solving gives the engine the same puzzle that appeared in the source.
Before solving, treat the region map as seriously as the givens. Count the cells in each saved region, scan for any blank or uncolored cell, and compare the outline with the original puzzle from top left to bottom right. If the puzzle came from a photo, check whether a heavy border has been blurred, because one unclear edge can join two regions that should be separate.
Next, review the givens as fixed clues rather than as working notes. A Jigsaw Sudoku solver assumes every entered digit is part of the puzzle. If you were experimenting by hand, erase guesses before pressing Solve. This habit separates puzzle errors from solving errors and makes the uniqueness report more useful.
For difficult puzzles, export the clean starting state before testing ideas. You can return to the original layout, compare a partial grid with the finished answer, or share the exact custom regions. Because irregular Sudoku depends on both digits and shapes, a screenshot of numbers alone is not enough.
For puzzle makers and teachers
A Jigsaw Sudoku solver is not only an answer checker. It is a useful design tool. Puzzle makers can test whether a region pattern supports interesting logic, whether a clue set has a single solution, and whether a puzzle remains fair after removing clues. Region shape matters: long narrow regions create different interactions from compact regions, and symmetrical layouts often feel different from chaotic ones.
Teachers can use Jigsaw Sudoku to show that logic depends on constraints, not on the visual habit of 3x3 boxes. Students who already understand Sudoku can see how changing one rule changes the solving process. The region editor also makes it possible to demonstrate mistakes: move one cell into the wrong region, solve again, and show how the entire logic changes.
If you would rather solve than check, there is a daily jigsaw sudoku, and the printable jigsaw sets are 100 puzzles apiece with the answers in the back. For everyday solvers, the practical benefit here is simple. You can draw the puzzle as printed, check your work, recover from a stuck position, and learn which irregular-region patterns matter. Whether you call it Jigsaw Sudoku, Irregular Sudoku, Nonomino Sudoku, or Region Sudoku, this solver is built to handle the custom shapes that define the puzzle.
Learning from the solved grid
After the solver completes the grid, do not only copy the answer. Look at placements forced by unusual region shapes. Many Jigsaw Sudoku breakthroughs come from a region that occupies several cells in one row or column, creating eliminations that would not exist in classic Sudoku.
If the puzzle has multiple solutions, compare the flexible areas. They often reveal where another given is needed or where the design is too open. If there is no solution, compare the first contradiction with the region borders. Most failed entries come from the map, not from arithmetic.