Nonogram rules

A nonogram grid has rows and columns of empty cells. Numbers next to each row and column are the clues.

A clue such as 3 1 means two blocks in that line. The first block has 3 filled cells. The second block has 1 filled cell. The blocks appear in the same order as the clue numbers. In a row, that order runs left to right. In a column, the order runs top to bottom, as the Wikipedia article on Nonograms explains.

Each block needs at least one empty cell before the next block of the same colour. A clue of 0 means the line stays empty.

You mark cells with one of two symbols while you solve a puzzle. A filled cell is part of a picture block. An X marks a cell that must stay empty.

The X mark is optional for reaching the solution. Many players use X marks to record cells that are already ruled out. Marking a cell with X can prevent you from testing it again by mistake.

This example uses a 5 by 5 grid. The row clues, from top to bottom, are 1, 1, 5, 1, 1. The column clues, from left to right, are also 1, 1, 5, 1, 1.

Row 3 has a clue of 5. Because the grid is 5 cells wide, the whole row must be filled. Column 3 has the same clue. The whole column must be filled too.

Row 1 has a clue of 1. Cell 3 in row 1 is already filled, from the column 3 deduction. That one filled cell already satisfies the row 1 clue. Every other cell in row 1 must stay empty.

The same logic solves every other line with a clue of 1. Those lines are rows 2, 4 and 5, and columns 1, 2, 4 and 5. Each of those lines has exactly one filled cell, where it crosses row 3 or column 3. Every other cell in those lines stays empty.

The finished picture is a plus sign. Here is the solution, row by row, with # for a filled cell and . for an empty cell.

Row 1: . . # . .
Row 2: . . # . .
Row 3: # # # # #
Row 4: . . # . .
Row 5: . . # . .

Every step in this example uses only the clues and already known cells. No step needs a guess.

A finished line should match its clue exactly. If a row or column does not match, one of its cells is wrong.

Check tools compare your board to the solution and mark wrong cells. Use a check often while you learn, so you catch mistakes early. Once you trust your logic, check less often and finish the puzzle on your own.

A colour nonogram uses two to four colours instead of one. Each clue number is shown in the colour of its block.

Two blocks of the same colour always need at least one empty cell between them. The same rule applies to black and white puzzles. Two blocks of different colours can sit right next to each other. No empty cell is required between different colours, as the Wikipedia article on Nonograms explains.

A puzzle is line-solvable when you can find the full solution from the row and column clues alone. You work one line at a time and never need to guess a cell. Jan Wolter's survey on webpbn.com defines the term this way.

Every puzzle on this site is line-solvable. The generator only keeps puzzles that have exactly one solution and need no guessing.

This site rates each puzzle by the hardest technique its solution needs, not by size. A larger grid is not always harder to solve.

Easy puzzles need only overlap and edge logic, the simplest techniques. Medium puzzles add glue, forcing and punctuating. Hard puzzles need full line logic and many passes over the whole grid before they are solved.

Read the techniques guide for a full explanation of each technique.