Nonogram — play the free picross number-logic puzzle in your browser

A nonogram — also called picross, griddler or paint-by-numbers — hides a pattern behind arithmetic. Every row and every column carries a list of numbers giving the lengths of its blocks of filled squares, in order, with at least one blank between consecutive blocks. A row labelled 3 2 on this 8-wide board has a run of three filled squares, then a gap, then a run of two, and nothing else. Your job is to work out exactly which squares those are.

This version is an 8×8 grid, free, in the browser, with no download and nothing to install. You get three lives: fill a square that should be blank and you lose one, and the square is crossed off for you so the mistake at least tells you something. Your score is how long the solve took, so faster is better — and the clock does not start until your first tap, which means you can read the clues for as long as you like before committing. Every board is generated fresh and then verified by a solver, so you never have to guess.

How to play

• Tap a square to fill it. Filled squares are the picture; the numbers describe them.
• Switch to ✕ mode with the button to mark squares you have proved are blank. On desktop you can also hold Shift or right-click to use the other mode without switching.
• Marking ✕ is always free — it is only a note to yourself, and tapping it again clears it. Only a wrong fill costs a life.
• Three lives. Run out and the run ends with no time banked, because an unfinished board has no solve time to rank.
• When a line's numbers are all satisfied, its clue dims and the rest of that line is crossed off automatically.
• Fill every square the clues call for to win. Press Space, Enter or F to switch modes mid-solve; Space or Enter starts a new puzzle from the menu.

Overlap and forcing: how to open a nonogram without guessing

The first move on any nonogram is overlap, and it is pure arithmetic. Take a row 8 wide with a single clue of 6. Push the block as far left as it goes and it covers squares 1–6; push it as far right as it goes and it covers 3–8. Squares 3, 4, 5 and 6 are covered either way, so they are filled — no matter where the block actually sits. The rule generalises: for a run of length r in a line of length n, the middle r − (n − r) squares are certain. On this 8-wide board that means any clue of 5 or more gives you free squares immediately, and clues that sum with their mandatory gaps to exactly 8 (3 4, 2 2 2) hand you the entire line at once.

The move most beginners skip is the one that actually unlocks the board: marking the squares you have proved are blank. A nonogram clue is a statement about uninterrupted runs, so a run cannot be measured until you know where it stops. Suppose a column reads 4 and you have already filled its second and third squares from crossings elsewhere. That tells you very little on its own. Cross off the top square — because a neighbouring row proved it empty — and the 4 is suddenly forced to occupy squares 2–5, filling two more squares and, in turn, blanking squares 6, 7 and 8. Each ✕ is a wall, and walls are what convert a vague clue into a determined one. Players who only fill squares stall on boards that are completely solvable; players who cross off blanks as diligently as they fill blocks cruise through them.

From there the loop is simply: work the line with the most information, write down everything it forces, then look at the crossing lines it just changed. Boards here are dealt only after that exact loop — a line solver that repeatedly intersects every legal placement of a clue against what is already known — has proved it finishes the whole grid, so if you are stuck, there is always another line where the deduction is waiting. About two in three random boards pass that test; the ones that would need a coin-flip are thrown away and regenerated before you ever see them.

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