How to play Nonogram

A nonogram is a picture hidden in a grid. Beside every row and above every column is a list of numbers, and each number is a run of filled cells in that line, in order. A row marked 3 1 holds a run of three filled cells, then at least one empty cell, then a single filled cell - but where those runs sit is for you to work out. Put the rows and the columns together, one line at a time, and the picture appears.

Nonograms are also known as Japanese crosswords, paint by numbers, griddlers and hanjie. On skill.games every puzzle is new: it is drawn by the game when you start, and it is checked before you see it. Each one has exactly one solution, and you can always reach it by reasoning about one row or one column at a time. You never have to guess and hope.

How to play on skill.games

When you open the game, the settings popup appears. Pick a difficulty - Easy, Normal, Hard or Crazy - and how mistakes are handled (see "Mistakes" below), then press PLAY. Your choices are remembered for next time. A new puzzle takes a moment to draw.

• Filling cells: tap a cell to fill it. Tap it again to clear it. On a computer, click.
• Painting runs: put your finger on a cell and drag along the row or the column. Every cell you pass over is filled, so a run of seven takes one stroke. The stroke stays on the line you started along, and if you drag back, the cells you leave are cleared again.
• The first cell decides: a stroke that starts on an empty cell fills empty cells; one that starts on a filled cell clears filled cells. Nothing else is changed along the way.
• Marking empty cells: switch the tool at the bottom of the screen from the filled square to the cross. Now taps and strokes put crosses in cells you know stay empty. Crosses are only notes for you: the game never needs them. On a computer, right-click or right-drag to cross.
• Undo: the UNDO button takes back your last stroke, as many times as you like. It's free.
• Zooming: the large grids can be zoomed on a phone. Pinch with two fingers or tap the magnifier button; drag the numbers along the edge, or use two fingers, to move around. The numbers stay pinned to the edges, so you can always see the clues for what is on screen. On a computer, the mouse wheel zooms.
• Keyboard: Z undoes, X or the space bar switches between filling and crossing, + and - zoom.

The row and column of the cell under your finger are lightly highlighted, so you can follow the line to its clue. When a line's filled cells match its numbers exactly, its numbers turn grey. The clock at the top shows your time.

The menu button in the top-left corner pauses the game and the clock, starts a new game or switches the sound on or off. The game is saved as you play, so if you close the page you can press CONTINUE and carry on with the same puzzle.

Rules

The clues. The numbers beside a row (and above a column) are the lengths of the runs of filled cells in that line, from left to right (or top to bottom). Runs are separated by at least one empty cell. A 0 means the whole line is empty.

The goal. Fill exactly the cells of the hidden picture. The puzzle is solved the moment every row and column matches its numbers - crosses don't matter, and you don't need to mark the empty cells.

Mistakes. In the settings you choose one of two ways to play:

• Unlimited: nothing is checked while you paint. You can fill a wrong cell and find out later, when a line refuses to fit. Most players find this the purest way to play.
• 3 lives: every cell is checked as you mark it. Filling a cell that belongs empty puts a red cross there instead; crossing a cell that belongs filled fills it with a red dot. Either way the cell is locked and costs one life, and a stroke stops at the mistake. The third mistake ends the game. Undo never gives a life back.

A puzzle you leave unfinished for a new one counts as a loss in your statistics.

Solving techniques

Every puzzle here can be finished with the techniques below, applied one row or column at a time. The higher levels need the later ones more often.

• Big runs overlap. In a line of 10, a run of 7 must cover the middle cells whichever way you push it: pushed fully left it covers cells 1 to 7, fully right cells 4 to 10, so cells 4 to 7 are filled for sure. Do the same with several runs: push them all as far left as they go, then as far right, and every run covers the cells where its two positions overlap.
• Count the line. Add up the numbers and the gaps between them. If a row of 10 says 4 5, that's 4 + 1 + 5 = 10: the line is completely determined.
• Empty lines and zeros. A 0 line is all empty. Cross it out straight away; it often gives the crossing lines a start.
• Cells nobody can reach. Once some cells are known, the runs can no longer go everywhere. Cells that no run can reach are empty - cross them.
• Use the edges. A filled cell at the very edge of a line must belong to the first run, so the run's full length can be filled from the edge and the next cell crossed.
• Finished runs get caps. When a run is complete, the cells on both sides of it are empty. Crossing them is often what unlocks the line next to it.
• Work back and forth. Every cell you settle in a row is a new clue for its column, and the other way round. Go over the lines that changed since you last looked.
• When the simple tricks stop. On Hard and especially Crazy you will reach points where pushing runs left and right doesn't settle anything new. Then think about all the ways a line can still be filled: a cell that is filled in every possible arrangement is filled, and a cell that is empty in all of them is empty, even when no single overlap shows it. Lines with many small runs and a few known cells are the usual place to find these.

Strategy tips

• Start with the biggest numbers. Runs that are long compared with their line give the most overlap, and on a blank grid they are the only place to start.
• Cross as you go. Crosses cost nothing and make the next deductions visible. A line with its runs placed and the rest crossed is finished and won't distract you again.
• Grey numbers are free information. When a line's numbers turn grey, its filled cells already match. Cross the rest of the line if you haven't.
• On the big grids, zoom in on one area. Finish a corner or a band of rows before moving on; the clues stay visible while you scroll.
• For a fast time, paint long runs with one stroke instead of separate taps, and don't spend strokes on crosses where you can simply carry on filling.
• If you're stuck, look at the lines that changed last. A newly settled cell matters only to the line that crosses it, and that line is usually where the next step is.

Difficulty levels

The difficulty sets the size of the grid and how deep the logic goes. Every puzzle is checked by a solver that works one line at a time, the way you do.

• Easy: 5 by 5. Solved in a few quick passes over the lines with simple overlaps.
• Normal: 10 by 10. Overlaps and reaching are enough, but the deductions chain from line to line.
• Hard: 15 by 15. Long chains of deductions; now and then a line needs every arrangement considered.
• Crazy: 20 by 20. The biggest grid, built so that you will hit several points where the simple tricks stop and only careful reasoning about a whole line gets you further.

The results screen shows your time, your best time at that difficulty (marked when you set a new one), the mistakes you made when playing with 3 lives, the size of the grid and the puzzle's code. Your statistics - wins, losses, win rate and streaks - are kept separately for each difficulty.