The rules of a nonogram fit in one paragraph. The numbers beside each row and column list the lengths of the unbroken runs of filled cells in that line, in order, with at least one empty cell between them; fill the grid so every line matches its numbers, and a small picture appears. Most explanations stop there. But that paragraph leans on a handful of rules it never states — about gaps, edges, and what the clues leave out — and the unstated ones are where beginners actually stumble. Here is the whole contract.
What are the rules of a nonogram?
Fill cells so that every row and every column matches the clue beside it. Each number in a clue is one unbroken run of filled cells; runs keep the clue’s order, never touch one another, and account for every filled cell in the line. That is the entire game. Spelled out, it comes to eight rules:
- Each number is one run. A clue number gives the exact length of one unbroken block of filled cells in its line. A 4 means four filled cells side by side — never three, never five, never four scattered.
- Runs keep the clue’s order. A row’s clue reads left to right and its runs sit left to right; a column’s clue reads top to bottom and its runs sit top to bottom. The first number is always the first run.
- Runs in the same line never touch. At least one empty cell separates consecutive runs — at least. One is the minimum gap, not its size.
- Runs owe the edges nothing. Any number of empty cells may sit before the first run and after the last, including none.
- The clue is a complete inventory. Every filled cell in the finished line belongs to exactly one clue number. No stray cells, no extra runs, nothing the numbers do not mention.
- A clue of 0 is an inventory with nothing in it. The line contains no filled cells; all of it stays empty.
- Every cell answers to two clues at once. It sits in exactly one row and one column, and the finished grid must satisfy both.
- The grid is solved when every line matches its clue. Not when the picture looks right — when the counts are right. The picture is a consequence of the rules, not one of them.
The contract is the same under every name the puzzle wears — picross, griddlers, and hanjie are publishers’ labels for identical rules. Learn it once and every masthead’s grid opens the same way.
What does a legal line look like?
Take a row ten cells wide with the clue 3, 2. The rules allow more arrangements than most beginners expect, and forbid three kinds of mistake worth naming.
All of these are legal: three filled cells at the left edge, one empty cell, then two filled — the tightest version. Three at the left edge and the two-run pushed to the far right, five empties between them. Four empties first, so the three-run sits in cells five through seven and the two-run ends the row. The gap stretches, the runs float free of the edges, and every version honors the same clue.
None of these is: a two-run placed before the three-run — order broken. Three filled cells with two more directly against them — the gap gone, and the line now shows a single run of five the clue never promised. A legal three and two plus one extra filled cell near the end — a third run the inventory does not list.
The clue never says where its runs sit. It says what they are: three then two, separated, complete. Where they sit is the whole puzzle.
Which rules do beginners misread?
Three, reliably. The minimum gap gets read as the exact gap. The first run gets assumed to start at the edge. And the clue gets treated as a partial list instead of a complete one. Each misreading produces confident marks with no rule behind them.
The gap first. Between two runs there is at least one empty cell, and the gap can be any size the line affords. A clue of 4, 2 on a ten-cell row can hold its runs one, two, three, or four cells apart — all four versions legal. Reading 4, 2 as “four cells, one gap, two cells” solves a stricter puzzle than the one in front of you.
The edge next. Nothing pins the first run to the border. A lone 6 on a fifteen-cell row has ten legal starting cells, exactly one of which touches the left edge. Where the run actually begins is deduction’s job; the rules only rule placements out.
And the inventory. The clue lists everything. Once a line’s runs are all found, every remaining cell is empty — not unknown, not probably: empty. This is also why the rules never need to mention the small X most solvers write in proven-empty cells. The X is not in the contract; it is how you keep what you have proven, and the line-by-line discipline treats it as half the game.
How do the rules change in color nonograms?
One clause moves, and only one. Clue numbers take the color of their runs, and the mandatory gap now applies only between runs of the same color — differently colored runs are allowed to sit directly against each other. Everything else, from run order to the complete inventory, carries over unchanged.
Wikipedia’s summary of the rules puts the new freedom concretely: a black 4 followed by a red 2 can mean four black cells, some empty space, then two red — or four black cells with the two red ones immediately against them. Both readings stay legal until the crossing lines settle which is true. The puzzle archive Nonograms.org words the other half plainly: in color puzzles, an empty square still separates groups of the same color.
Color adds vocabulary, not grammar. If the black-and-white rules feel settled in your hands, the colored ones are the same eight in brighter ink.
Do the rules promise one solution?
No — but every good nonogram has exactly one solution. Read the eight rules again and notice that none of them promises it: uniqueness is a design standard, built in by the maker, never guaranteed by the grammar.
The smallest grid in the game shows how the grammar falls short. Take a 2×2 square and give every row and every column the clue 1. Fill the top-left and bottom-right cells: each line holds exactly one filled cell, and all eight rules are satisfied. Now fill the other diagonal instead. Satisfied again. Two different pictures, both perfectly legal — and no deduction can choose between them, because there is nothing to deduce. The first certain cell never arrives; the grid simply waits for you to guess.
Behind that toy example sits real mathematics. Handed an arbitrary clue set, even deciding whether any solution exists is NP-complete — computer science’s label for problems where checking an answer is quick but finding one has no known fast method. That is the puzzle’s own experience written as theory: confirming a finished grid matches its clues is a minute’s work, while producing that grid is the whole game. A constructor who wants a grid with exactly one solution, reachable by logic alone, has to build toward it deliberately.
Most of the puzzles you will meet are built exactly that way. The main requirement of the craft, as the puzzle archives put it, is one logical solution, reachable without trial and error — and well-made collections hold themselves to it. But a carelessly generated grid can obey every rule on this page and still break the promise. So if a puzzle ever genuinely offers you two answers, the fault belongs to its maker, not to your logic. The rules decide what is legal. The craft makes the one legal answer yours to find.
Where do the rules leave you?
At the start of the actual game. The rules fit on one page; playing is learning what they imply — that a crowded clue pins its middle cells before you mark anything, that an empty line’s X’s feed every column crossing it, that certainty in one direction becomes certainty in the other. None of that is written in the contract. All of it follows from it.
The opening moves are where implication starts to pay: empty and full lines first, forced lines next, then the guaranteed middles of the fattest clues. The rules are eight lines long. The game is everything they imply.
Questions
Do the numbers in a nonogram clue have to be in order?
Yes. Runs appear in exactly the order the clue lists them — left to right along a row, top to bottom down a column. A clue of 3, 1 can never legally place the single cell before the three-run.
Can two runs of filled cells touch each other?
Not in the same line of a black-and-white puzzle — at least one empty cell must separate them, or they would read as one longer run. In color nonograms, runs of different colors may sit directly against each other.
Are picross rules the same as nonogram rules?
Yes. Picross, griddlers, hanjie, and paint-by-numbers are publishers' names for the same puzzle, and every rule here applies unchanged. Individual apps may add features like timers or mistake penalties, but those belong to the software, not the puzzle.
Does the first run have to start at the edge of the grid?
No. The rules let the first run begin flush against the border or any distance into the line, and the last run end the same way. Where it actually begins is what deduction is for; the clue alone rarely pins it.