Nonogram Generator

What this generator does

Produces a nonogram — a grid where numbers along each row and column give the lengths of the filled runs in order — together with its solution. The guarantee is the part that takes the work: the clues are proved to admit exactly one picture, and to be reachable by line-by-line deduction alone, so no step of the solve requires a guess. Puzzles that fail either test are discarded and another is generated.

How to use this tool

1. Choose a grid size between 5 and 15.
2. Press Make nonogram.
3. Fill squares that the row and column clues force, and cross out the ones they rule out.
4. Reveal the picture when you are finished, or print the grid to solve on paper.

Understanding the controls

Grid size

Between 5 and 15 squares each way. Size affects how long a puzzle takes far more than how hard it is: a 15x15 that solves in three passes is easier than a 10x10 that needs seven, which is why the difficulty shown is measured rather than assumed from the size.

Shape

Square or oblong. Non-square grids behave slightly differently — the shorter dimension tends to give up its cells first, which changes where a solve naturally starts.

Seed

Leave it blank for a new puzzle each time. Enter a word and the same puzzle comes back, so a class can all work on the identical grid or a lost sheet can be reprinted.

Worked examples

A 10x10

Clues like 3 1 2 down the side and 4 2 across the top; one picture fits them all.

The ambiguous case that is rejected

Rows [1],[1] with columns [1],[1] — two diagonals, identical clues, no puzzle.

Difficulty is measured

'Line solving needed 7 passes' rather than a guess from how full the grid is.

Reprintable

The seed 'friday-quiz' always produces the same grid.

Common use cases

• A logic starter that needs no explanation beyond the rules
• Printable puzzles for a cover lesson or a quiet activity
• Practising deduction where every step can be justified rather than guessed
• Puzzle pages for a newsletter or a club sheet
• Teaching that a puzzle needs a unique solution to be a puzzle at all

How this generator works

The generator proposes a random pattern of filled squares, derives the row and column clues from it, then throws the pattern away and solves the clues from scratch. The solver uses one rule and no others: for each line, enumerate every arrangement of its clues consistent with what is already known, and fill in any square that every arrangement agrees on. It repeats over rows and columns until nothing changes. If that reaches a complete grid, the puzzle has exactly one solution and needs no guessing, and it is offered. If squares remain unknown, the clues are ambiguous and the puzzle is thrown away. The classic failure this catches is the 2x2 switch — four squares at the corners of a rectangle whose two diagonals produce identical clues, so nothing can distinguish them.

Randomness and fairness

The candidate pattern is drawn with the browser's cryptographic random number generator, and everything after that is deterministic: the clues follow from the pattern and the uniqueness check follows from the clues. A seed switches to a reproducible generator so the same puzzle can be printed twice; that mode is deterministic, not cryptographic, which is exactly what makes it reproducible.

For how randomness is produced across the whole site, see how Generate Random works.

Assumptions this tool makes

• Clues read left to right for rows and top to bottom for columns, with at least one blank square between runs, which is the standard convention.
• A row or column with no filled squares is written as 0.

Limitations and good to know

• Only black-and-white nonograms. Multi-colour variants have a different clue format and a different solving procedure, and are not generated here.
• Grids are capped at 15 squares each way. The uniqueness check enumerates line arrangements, which stays fast at these sizes and does not beyond them.
• Puzzles are random patterns rather than recognisable pictures. A nonogram whose solution is a cat needs a hand-drawn bitmap, and this generates rather than draws.
• Difficulty describes how much deduction the solve needs, not how long it feels. A large gentle grid can take longer than a small tricky one.
• It has no solving surface — squares are not clickable. Print it or copy the clues into your own grid.

Common mistakes

Guessing when a line seems stuck

No puzzle here needs a guess. If a line will not move, another line has information you have not used yet — work the columns against the rows rather than pressing on down one.

Only marking filled squares

Cross out the squares you have ruled out as well. Known-empty squares constrain the neighbouring lines just as strongly as known-filled ones, and leaving them blank throws that away.

Reading a clue as positions rather than lengths

A clue of 3 1 means a run of three, then at least one gap, then a run of one — somewhere in that line. It says nothing about where they start.

Practical tips

• Start with the longest clues in the largest lines. A run of 8 in a 10-wide row overlaps itself no matter where it sits, so it hands you filled squares immediately.
• When a row is finished, immediately cross out the empty squares in it. That is usually what unlocks the columns.
• For a class, use a seed and print once. Everyone working the same grid makes it possible to talk about a step rather than about a puzzle.

Troubleshooting

I reached a contradiction

Something earlier was filled in on an assumption. Every puzzle here is solvable by deduction alone, so a contradiction means a guess was made — retrace to the last square you were certain about.

The generator says it could not find a puzzle

Random patterns are often ambiguous, and at some sizes the search occasionally comes up empty rather than serving something unchecked. Press again, or change the size slightly.

Privacy and your data

Nothing is entered and nothing is stored. Puzzles are generated in your browser, no grid is uploaded or written into the page address, and analytics records only that the tool ran and at what size — never a puzzle or its solution.

Frequently asked questions

How do you know there is only one solution?

Because it is solved before it is offered. The generator derives the clues from a pattern, discards the pattern, and then solves the clues from nothing using line deduction only. Reaching a single complete grid that way proves both that the solution is unique and that no guessing is needed. Anything that does not reach one is discarded.

Is a nonogram the same as a picross?

Yes. Nonogram, picross, griddler, hanjie and paint-by-numbers are all names for the same puzzle. The rules and the clue format are identical.

Why not bigger grids?

The uniqueness check enumerates the possible arrangements of each line, which is fast up to about fifteen and grows sharply beyond it. Rather than drop the check for larger grids — which would mean dropping the guarantee that makes these puzzles — the size is capped.