What are the three Hitori rules?

Among unshaded cells, each number may occur at most once in a row and at most once in a column. Shaded cells cannot share a horizontal or vertical edge, although diagonal contact is allowed. Every unshaded cell must connect to every other through horizontal and vertical steps. Mark every cell Shade or Keep before the board can be complete.

Which board sizes are supported?

Choose any square size from 4 by 4 through 8 by 8 and a whole-number seed from 0 to 4294967295. The version 1 generator constructs an original numbered board and counts solutions up to two. It publishes only a proved unique candidate, within 512 candidate attempts, 250000 search nodes and an eight-second worker limit. A failed or canceled generation keeps the previous puzzle.

How do I use the keyboard?

Tab to a numbered cell and use the arrow keys, Home or End to move focus. Press S to shade, U to keep unshaded, or X, Delete or Backspace to clear to Unknown. Enter and Space apply the selected Shade, Keep or Unknown tool. The grid scrolls within its own region on narrow screens, and every cell has a 44-pixel target and a spoken row, column, number and current state.

Does Check rules reveal an answer?

No. The displayed feedback evaluates only your current marks against the three rules. Unknown cells may still connect white regions, so an unfinished board without a current conflict is not necessarily solvable. Show one cell corrects a cell using the verified solution; that hint, revealing the solution or printing an answer key makes an unfinished run assisted practice.

How does the 6 by 6 challenge work?

Complete a fresh canonical 6 by 6 board without answer assistance. The score is max(0, 1000 minus final decisive moves), from 0 to 964; higher is better. A decisive move changes a cell to Shade or Keep. A repeated mark or clearing to Unknown adds none. Undo removes the undone decisive move, and redo restores it, so only the retained history counts. The recipient explicitly starts the same seeded board, completes it, sees both self-reported scores and the signed difference, then shares a new link with their score.

Why is a repeated or restored board practice only?

Previously opened boards, hints, revealed answers, restored sessions and sizes other than 6 by 6 cannot produce a fresh canonical score. Exposure is tracked by the actual numbered board as well as the seed, including rotations, reflections and a global renaming of its numbers. Reviewing an already completed fresh result preserves its earned score. Completed results remain fixed; use Replay same puzzle to practice again.

Can I save progress or print the puzzle?

Touched settings and recorded moves save under this tool's local browser key without the solution. On reload, Resume saved puzzle regenerates the seed, verifies the exact numbered board and checks the move history before restoring practice. If browser storage is blocked or full, the page reports it. Print puzzle includes only the original numbers. Print puzzle and answer key adds a separate requested solution page.

What is included in a shared link or result card?

A challenge link contains only the tool, seed, fixed 6 by 6 configuration and self-reported score. It contains no solution or move history. You can copy the link, use the device share dialog or download a 1200 by 630 PNG result card. The same score and comparison remain selectable as text when clipboard, share or image export is unavailable.

Hitori Puzzles

Shade cells so the kept numbers are unique in every row and column, shaded cells never share an edge, and all kept cells form one connected region. Generate an original numbered board, use keyboard or touch controls, undo decisions and print an exercise. Every offered puzzle has one solution proved by bounded exact search.

Original numbered puzzles. Every offered board has exactly one proved solution.

Choose a puzzle4 × 4 through 8 × 8

Board sizePuzzle seed

Seed: whole number from 0 to 4294967295.

All three Hitori rulesCurrent feedback

Unique kept numbers
Among unshaded cells, each number appears at most once in each row and in each column.

No shaded edge contact
Shaded cells cannot share a horizontal or vertical edge. Diagonal contact is allowed.

One connected white region
All kept cells connect through horizontal and vertical steps. Unknown cells must be decided before completion.

Original Latin-based construction adds repeated numbers, then exact search counts solutions up to two. Only a proved unique candidate is published, within 512 candidates, 250000 search nodes and an 8-second worker limit.

Choose a size and seed, then generate an original Hitori puzzle.

Board: Not started

Status: Not started

Decisive moves: 0

Unknown cells: Not started

Worked rules

Two kept 3s in one rowRepeated unshaded value
Invalid. At least one of those equal numbers must be shaded.
Two shaded neighborsHorizontal or vertical
Invalid edge contact. Shaded cells may meet diagonally.
An isolated white cornerBoth neighboring cells shaded
Invalid when other white cells remain. All white cells need a connecting path.

A decisive move changes a cell to Shade or Keep. Repeating its current mark or clearing to Unknown adds no decisive move. Undo removes the undone move, and redo restores it; only the final retained history is scored. Completed results remain fixed. Touched progress saves locally, without the solution, and is revalidated as practice on reload.

Accuracy. Unshaded numbers are unique within each row/column, shaded cells cannot share an edge, and all unshaded cells connect orthogonally. Uniqueness-checked original generation only.

Common questions

What are the three Hitori rules?: Among unshaded cells, each number may occur at most once in a row and at most once in a column. Shaded cells cannot share a horizontal or vertical edge, although diagonal contact is allowed. Every unshaded cell must connect to every other through horizontal and vertical steps. Mark every cell Shade or Keep before the board can be complete.
Which board sizes are supported?: Choose any square size from 4 by 4 through 8 by 8 and a whole-number seed from 0 to 4294967295. The version 1 generator constructs an original numbered board and counts solutions up to two. It publishes only a proved unique candidate, within 512 candidate attempts, 250000 search nodes and an eight-second worker limit. A failed or canceled generation keeps the previous puzzle.
How do I use the keyboard?: Tab to a numbered cell and use the arrow keys, Home or End to move focus. Press S to shade, U to keep unshaded, or X, Delete or Backspace to clear to Unknown. Enter and Space apply the selected Shade, Keep or Unknown tool. The grid scrolls within its own region on narrow screens, and every cell has a 44-pixel target and a spoken row, column, number and current state.
Does Check rules reveal an answer?: No. The displayed feedback evaluates only your current marks against the three rules. Unknown cells may still connect white regions, so an unfinished board without a current conflict is not necessarily solvable. Show one cell corrects a cell using the verified solution; that hint, revealing the solution or printing an answer key makes an unfinished run assisted practice.
How does the 6 by 6 challenge work?: Complete a fresh canonical 6 by 6 board without answer assistance. The score is max(0, 1000 minus final decisive moves), from 0 to 964; higher is better. A decisive move changes a cell to Shade or Keep. A repeated mark or clearing to Unknown adds none. Undo removes the undone decisive move, and redo restores it, so only the retained history counts. The recipient explicitly starts the same seeded board, completes it, sees both self-reported scores and the signed difference, then shares a new link with their score.
Why is a repeated or restored board practice only?: Previously opened boards, hints, revealed answers, restored sessions and sizes other than 6 by 6 cannot produce a fresh canonical score. Exposure is tracked by the actual numbered board as well as the seed, including rotations, reflections and a global renaming of its numbers. Reviewing an already completed fresh result preserves its earned score. Completed results remain fixed; use Replay same puzzle to practice again.
Can I save progress or print the puzzle?: Touched settings and recorded moves save under this tool's local browser key without the solution. On reload, Resume saved puzzle regenerates the seed, verifies the exact numbered board and checks the move history before restoring practice. If browser storage is blocked or full, the page reports it. Print puzzle includes only the original numbers. Print puzzle and answer key adds a separate requested solution page.
What is included in a shared link or result card?: A challenge link contains only the tool, seed, fixed 6 by 6 configuration and self-reported score. It contains no solution or move history. You can copy the link, use the device share dialog or download a 1200 by 630 PNG result card. The same score and comparison remain selectable as text when clipboard, share or image export is unavailable.

Unshaded numbers are unique within each row/column, shaded cells cannot share an edge, and all unshaded cells connect orthogonally. Uniqueness-checked original generation only.