The rules of nonograms

A nonogram is a grid with numbers running along the top and the left edge. Every cell is either filled or empty. The numbers tell you, for each row and each column, the lengths of the consecutive runs of filled cells in order. Solve the puzzle and a small picture appears.

That is the whole game.

The clue 3 on a row says: somewhere in that row, three filled cells sit next to each other, with empty cells on either side. The clue 3 1 says: a run of three, then at least one empty, then a run of one. Order matters; gaps are at least one cell wide. A clue of 0 (sometimes shown as a blank) means the row is entirely empty.

The puzzle is logically solvable from the clues alone — you never have to guess. If a puzzle has more than one valid solution it isn't really a puzzle, and good nonograms are designed so that exactly one combination of filled and empty cells satisfies every clue at once. That is the discipline the form holds itself to, and it's why every move you make can be justified by the numbers in front of you.

You'll often see solvers mark cells they've ruled out with a small X or a dot. Those marks don't solve anything on their own — the puzzle is finished when every filled cell is filled and every empty cell stays empty. The crosses are bookkeeping, and worthwhile bookkeeping at that, because a cell you've already eliminated isn't a cell you'll have to think about again. Most modern nonogram interfaces, including this one, give you a dedicated tool for X-marks alongside the fill tool.

Sizes range from a single-line warm-up to grids large enough that you'll want a cup of tea. The smallest sensible nonogram is around 5×5 — enough room for a clue or two per line, finishes in a minute. Standard sizes are 10×10 (the bread and butter), 15×15 (longer runs and more cross-line reasoning), and 20×20 (a proper sit-down). You don't need to start at the bottom, but starting at the bottom is more pleasant than people expect.