Usowan Puzzle Generator
Usowan — 'the liar' — is a shading puzzle where you cannot trust every number. The grid is cut into rooms. Each number counts the shaded cells beside it, except that in every room exactly one number is false. Shaded cells never touch side by side, numbered cells stay unshaded, and the unshaded cells all join up. This makes fresh puzzles at 6 or 7 squares a side, each with a single answer proved from the printed grid alone, and prints the puzzle and its answer in black and white.
What this generator does
Cuts the grid into rectangular rooms, draws a valid shading, gives every room one false number, then adds true numbers only until one answer remains and takes away any that turn out not to be needed. Hitori and Nurikabe trust every clue; here the deduction is finding which clue lies.
How to use this tool
- Choose the grid size and press Make a puzzle. Add a puzzle code if you want to make the same puzzle again.
- Solve with paper beside you, or print the puzzle and answer pages.
- Press Show the answer to check: shaded cells are dark and each room's false number is struck through.
Understanding the controls
- Grid
- 6 or 7 squares a side. 8 × 8 is not offered: proving one answer took up to nine seconds on a test machine, too long to hold up a page.
- Puzzle code
- Leave empty for a new puzzle from the browser's secure generator. With a code, the same code and size make the same puzzle again; the code is a seed, not a secret.
Worked examples
- Code harbour, 6 × 6
- 10 rooms and 18 numbers (10 of them false, one a room); 10 cells shaded.
- Code harbour, 7 × 7
- 14 rooms and 21 numbers (14 false); 13 cells shaded.
Common use cases
- A shading puzzle with a twist for solvers who know Nurikabe and Hitori
- A printed puzzle sheet with the answer on the next page
- A club or class working the same puzzle from a shared code
How this generator works
Rooms are rectangles of two to six cells cut by repeated splitting. A search decides each cell in reading order — shaded or not — never letting two shaded cells touch, and checks the unshaded cells can still join up; run once in a shuffled order it draws one genuine answer. Every room then gets one number on an unshaded cell that disagrees with the real count. The same search, now counting answers from the printed numbers alone, looks for a second answer: as each number's neighbours are all decided, it tallies false numbers room by room and abandons a branch with two false numbers in a room, or none once the room is complete. While a second answer exists, a true number goes on a cell whose count differs between the two. Then every true number is removed in turn and put back only if the count no longer finds exactly one answer. A search that reaches its step limit proves nothing, so that layout is dropped. Afterwards the answer is re-read against every rule, each room's false number is found again by counting, and the count is run once more from the printed puzzle; a stopped count shows as not decided.
Randomness and fairness
Rooms, the drawn shading, the false values and the choice of numbers come from a random sequence: the browser's secure generator, or a seeded one when you give a code. A code repeats a puzzle while the generator is unchanged. Codes are deterministic, not cryptographic.
For how randomness is produced across the whole site, see how Generate Random works.
Assumptions this tool makes
- Nikoli's published rules for Usowan, restated on the page.
- Rooms are rectangles, as in Nikoli's examples; every room holds at least one number, because it must hold a false one.
Limitations and good to know
- 6 × 6 and 7 × 7 only; about half the cells carry a number, because every room needs its false one.
- No difficulty grade is given; how hard a puzzle feels depends on where its false numbers fall.
- Rooms are generated, not hand-designed.
Common mistakes
- Trusting a number because it fits so far
- Every room has exactly one false number. Find it by playing numbers in the same room against each other.
- Counting diagonal neighbours
- A number counts only the cells directly above, below, left and right of it.
- Shading a numbered cell
- Numbered cells are never shaded, whether their number is true or false.
Practical tips
- A 4 beside any other number must be false: numbered cells are never shaded, so it cannot have four shaded neighbours.
- In a room with one number, that number is the false one — its count tells you only what is not there.
- Keep checking that the unshaded cells can still join up; it often decides a corner.
Privacy and your data
Usowan puzzles are made in your browser. With analytics consent, usage counts record that a puzzle was made or failed; the numbers, the shading and any puzzle code are never sent.
Related generators
- Nurimeizu Puzzle GeneratorMakes Nurimeizu puzzles — paint whole rooms so the white cells form a maze from S to G — each proved to have exactly one answer, with a printable answer page.
- Hitori Puzzle GeneratorShade out the repeats without letting two shaded cells touch or the rest come apart, with a single answer proved by construction and by search.
- Nurikabe Puzzle GeneratorNurikabe grids where each number is an island of that size, the wall is one piece, and no two-by-two block is allowed.
- Nuritwin Puzzle GeneratorMakes Nuritwin puzzles — shade two equal blocks in every region, all joined up — each proved to have exactly one answer, with a printable answer page.