The rules
The grid starts blank. Beside every row and above every column is a clue: one or more numbers. Each number is a block, a run of that many filled squares side by side.
- Order. The blocks appear in the order of the clue: left to right for a row, top to bottom for a column.
- Gaps. Two blocks in one line are separated by at least one empty square. Otherwise they would join into one longer block.
- Nothing else. Every square that is not part of a block is empty. A clue of 0 means the whole line is empty.
Fill exactly the right squares and you have solved it. Here is a small one, finished. Read the clues against the picture: the top row, 2 2, is two blocks of two with a gap; the second and third rows are one block of seven; the first column, 2, is the two filled squares near its top.
Most people mark the squares they know are empty with a cross (or a dot, on paper). Crosses are only notes: the puzzle is solved when the filled squares are right, crossed or not. But they help a great deal, because each cross tells the line running the other way that no block can pass there.
Technique 1: lines that fit only one way
Add up the clue’s numbers, then add one for each gap between blocks. If the total equals the length of the line, the blocks fit in exactly one way, packed from edge to edge. In a row of 10, the clue 3 1 4 needs 3 + 1 + 4 = 8 squares, plus 2 gaps: 10. So the row is filled at once, and its two gaps are crosses.
Technique 2: the middle of a long block
A block longer than half its line always covers the middle. Picture the block of 7 in a row of 10 pushed as far left as it goes (squares 1 to 7), then as far right (squares 4 to 10). Squares 4 to 7 are filled in both, and in every place between, so they are filled whatever the answer turns out to be.
The same works with several blocks. Push all of them to the left, then all to the right, and see where each block overlaps itself. In a row of 10 with 4 3, the 4 covers squares 1 to 4 or 3 to 6 (so 3 and 4 are filled), and the 3 covers 6 to 8 or 8 to 10 (so 8 is filled).
Short blocks in a long line give nothing at first: 1 1 in a row of 10 could sit almost anywhere. Leave such lines for later.
Technique 3: cross out what no block can reach
Once some squares are known, look at how far each block can stretch. In a row of 10 with the clue 3, suppose the second square is filled. The block of three must include it, so it starts at square 1 or 2 and ends by square 4. Squares 2 and 3 are filled either way, and squares 5 to 10 are out of its reach: cross them out.
Technique 4: finished lines
When a line holds every block of its clue, everything else in it is empty. A row of 10 with 2 2 that already shows two blocks of two needs no more fills: cross out the other six squares, and each of those crosses helps a column.
A whole puzzle, step by step
Put the techniques together and go back and forth: rows, then columns, then rows again. Here is a 5 by 5 puzzle from the start.
The rows first. The middle row’s 5 fills it from edge to edge. The 3s in rows 2 and 5 each cover the middle square of their row, wherever they sit. Rows 1 and 4 have short blocks and give nothing yet.
Then the columns. The first column’s clue is 1, and its middle square is already filled: that is its block, so the other four squares are crossed out. The same goes for the last column. The middle column, 3 1, needs 3 + 1 and a gap: 5 squares, so it fits only one way. The 4s in columns 2 and 4 cover their three middle squares, wherever they sit.
Rows again. Row 1 is 1 and already has its block in the middle; row 5’s 3 must run from the second square to the fourth. The last squares fall into place, and the picture is a little house.
When you get stuck
- Look at every line again. A cross you placed in a column ten minutes ago may now settle a row. Most stuck moments are a line you have not looked at since it changed.
- Count from the edges. Where a line starts with a filled square, the first block starts there; where a crossed square sits close to the edge, a long first block cannot fit before it.
- Mind the biggest block. If a gap between crosses is too short for any block that could go there, cross the whole gap out.
- Check your work. One wrong fill makes later lines look impossible. On this site, a clue turns red when your marks rule it out, and Check shows any wrong square.
Every nonogram on this site can be solved with these techniques alone: each one is worked through line by line before you see it, so you never need to guess. If you do get stuck, Hint settles one row or column and says why in a sentence.
Playing on this site
Tap a square to fill it, drag along a line to fill several, and switch to Cross to mark empty squares (with a mouse, the right button crosses out). Undo takes back a whole drag at once. Clues fade when their line is complete. There are three sizes, Easy, Medium and Hard, and a daily nonogram that is the same for everyone each day.