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What is a nonogram?

A nonogram (also called Picross or Griddler) is a logic puzzle where you must fill in cells on a grid according to numerical clues given for each row and column. The numbers tell you how many consecutive filled cells appear in each line, separated by at least one empty cell.

The overlap method

For a clue of length k in a row of length n, the run must fit somewhere within n cells. The cells in the overlap zone - the middle (2k − n) cells - are guaranteed filled regardless of where the run starts.

Example: clue 6 in a 10-cell row. The run could start as early as cell 1 (fills 1–6) or as late as cell 5 (fills 5–10). Cells 5–6 are covered in both cases - they are definitely filled.

Clue: 6  in 10 cells
Earliest: [■ ■ ■ ■ ■ ■ □ □ □ □]
Latest:   [□ □ □ □ ■ ■ ■ ■ ■ ■]
Overlap:  [        ■ ■         ]
                  ^5 ^6

Solving techniques

Full determination: if the sum of all run lengths plus minimum gaps equals the line length, every cell's state is known. Example: clues 3 2 in 6 cells -> only one arrangement fits: [■ ■ ■ □ ■ ■].
Cross-hatching: use a confirmed cell in a row to restrict which columns that run can occupy, and vice versa. Switch between row and column constraints repeatedly to narrow down unknowns.
Forced empty cells: after placing a run, the cells immediately before and after it must be empty. Mark them with ✕ to prevent accidental fills.
Edge anchoring: if the first clue value equals or nearly equals the distance from the edge, the run is pinned - it cannot start far from the wall.

Controls

Action	Control
Fill a cell	Left-click / tap
Mark cell empty (✕)	Right-click / long press
New puzzle	New Game button

Solving logic by clue type

Clue pattern	Guaranteed result	Example
Single clue = row/column length	Fill the entire line	Clue: 10 in 10-cell row -> all cells filled
Clue of 1 in a 1-cell gap between filled/marked cells	That cell is definitely filled	✕ _ ✕ with clue 1 -> middle cell is ■
Sum of clues + minimum gaps = row length	Entire row is fully determined	Clues 3,2 in 6 cells: 3+1+2 = 6 -> [■■■□■■]
Clue larger than half the row length	Overlap zone is always filled	Clue 6 in 10: cells 5–6 guaranteed filled

History of nonograms

Nonograms were invented independently by two Japanese puzzle designers in 1987: Non Ishida created a painting competition where participants guessed an image from a number grid, and Tetsuya Nishio published logic picture puzzles in a Japanese magazine. The name "nonogram" is attributed to Non Ishida.

They were introduced to Western audiences by James Dalgety, who licensed the puzzle to the Sunday Telegraph as "Griddlers" in November 1990. Nintendo popularized them in video games as the Picross series (first released 1995), which has sold millions of copies and continues with new entries.

Difficulty scaling

Several factors make a nonogram harder:

Grid size: more rows and columns increase the number of constraints to track simultaneously.
Cross-row/column interdependence: when determining a cell requires reasoning about multiple rows and columns simultaneously rather than one line at a time, difficulty spikes.
Sparse clues: rows with many short clues leave more possible arrangements than rows with one large clue.
Unique solvability: well-designed nonograms have exactly one solution reachable by logic alone - no guessing required. Puzzles that require trial and error are considered poorly constructed by the community.

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