What is a Nonogram solver?
A Nonogram solver is a tool that takes the number clues from a picture logic puzzle and calculates which cells must be filled and which must stay empty. Nonograms are also widely known as Picross, Griddlers, Hanjie and Japanese crossword puzzles, so the same solver can help with all of those names.
The clues describe runs of filled cells. A row clue of 4 2 means there is a block of four filled cells, at least one empty cell, then a block of two filled cells. The solver compares every row clue with every column clue until the only matching picture grid remains.
- Enter row clues and column clues from a puzzle.
- Check whether the clues have a valid answer.
- Reveal the completed picture grid.
- Spot clue sets that are impossible or ambiguous.
How to use this Nonogram solver
Start by choosing the width and height of the puzzle. Width means the number of columns, and height means the number of rows. Then choose the group size, which controls how many clue number boxes appear for every row and column.
After you create the grid, type the column clues above the board and the row clues beside the board. Leave unused boxes blank. If a whole line has no filled cells, you can leave it blank or enter 0. Press Solve to calculate the answer.
- Choose Width, Height and Group size.
- Press Create grid.
- Enter the column clues from top to bottom.
- Enter the row clues from left to right.
- Press Solve to fill the answer grid.
How Nonogram clues work
Every clue number is a length of a filled block. Multiple numbers in one line always appear in the listed order, and separate blocks need at least one empty cell between them. The spaces before the first block and after the last block can be any length, including zero.
That simple rule is what makes Nonograms logical. If a run is long enough that all possible placements overlap, the overlapping cells must be filled. Once a run is fixed, the cells around it often become empty separators.
- A clue of 5 fills one group of five cells.
- A clue of 1 1 fills two single cells with at least one empty cell between them.
- A clue of 0 or a blank line means no cells are filled in that line.
- Rows and columns must agree on the same filled cells.
Why a puzzle can have no solution or many solutions
A valid Nonogram needs row clues and column clues that describe the same total number of filled cells. If the row clues add up to 32 filled cells but the column clues add up to 30, no solution can exist.
Some clue sets are balanced but still ambiguous. That means more than one picture grid satisfies every clue. A good published Nonogram usually has one unique solution, because uniqueness lets solvers progress by logic instead of guessing.
How this Nonogram solver works
The solver first generates all legal patterns for each row and column. It then removes patterns that contradict confirmed cells. Whenever all remaining patterns for a line agree on a cell, that cell is forced.
If forced logic does not finish the grid, the solver uses a controlled backtracking search. It chooses the row or column with the fewest remaining possibilities, tests one pattern, and keeps only branches that still satisfy every crossing clue.
How to solve a Nonogram by hand
You do not need the solver to enjoy Nonograms — they are designed to be cracked by pure logic. Start with the most constrained lines. When a clue's blocks plus the gaps between them nearly fill the line, the overlap method guarantees cells: slide the blocks as far one way as they go, then as far the other, and any cell covered both times must be filled.
Then alternate between rows and columns, letting each filled cell narrow the crossing lines. Mark cells you have proven empty with a dot or cross, not just the filled ones — those marks are what stop blocks from spreading too far. A finished line's clue can be ticked off so you do not re-read it.
- Begin with the rows and columns whose clues leave the least slack.
- Use the overlap method for any block longer than half its line.
- Mark certain empty cells with a dot or cross, not only filled cells.
- Alternate between rows and columns as new cells appear.
- Use the solver afterwards to confirm your answer.
Picross, Griddlers, Hanjie and the Nonogram name
Nonograms go by many names. The puzzle was popularised in 1980s Japan, and the name 'Nonogram' comes from Non Ishida, the designer credited with bringing it to a wide audience. Nintendo's Picross games carried it to consoles worldwide, while British newspapers printed it as Hanjie and the name Griddlers spread through puzzle magazines and websites.
Despite the different labels, the rules never change: number clues give the lengths of filled runs in each row and column, and you shade cells to reveal a hidden picture. Because the mechanics are identical, this solver handles Picross, Griddlers, Hanjie and Japanese crossword puzzles equally well.
Using the solver to design and check Nonograms
The solver is just as useful for making puzzles as for solving them. If you have drawn a picture and want to turn it into a Nonogram, work out the clues, then feed them back into the solver to check the result. A good puzzle should solve to exactly one picture; if the solver finds several, the clues are ambiguous and the design needs tightening.
Two quick quality checks help. First, the row clues and column clues must describe the same total number of filled cells, or no solution exists at all. Second, aim for puzzles the forced-logic stage can finish without backtracking, because those are the ones a person can solve by reasoning rather than guessing.
- Solve your own clues to confirm a single, unique picture.
- Multiple solutions mean the clues are ambiguous — tighten them.
- Check that the row and column clue totals match.
- Prefer puzzles solvable by logic alone, without guessing.
- Re-check after any edit to the picture or the clues.