Nonogram

Nonograms go by a few names — Picross, Griddler, Hanjie, pixel puzzle. The rules are always the same: you get a rectangular grid and a set of number clues for each row and column. The clues describe consecutive groups of filled cells, left to right (for rows) or top to bottom (for columns). Your job is to figure out which cells to fill and which to leave empty.

Smaller grids (5×5) can often be solved by trial and error. That stops working around 10×10. If you want to solve larger puzzles reliably, you need a few techniques. Here they are.

Reading the clues

A clue like [3] on a 5-cell row means there are exactly 3 consecutive filled cells somewhere in the row. The remaining 2 cells are empty.

A clue like [1 2] means: 1 filled cell, then one or more empty cells, then 2 filled cells. The groups always appear in the order listed, and there's always at least one empty cell between them. The minimum space this clue needs is 1 + 1 (gap) + 2 = 4 cells.

A clue of [0] means the whole line is empty. A clue of [5] on a 5-cell line means the whole line is filled. These are free — fill or X-mark the entire line immediately.

Overlap logic (the core technique)

This is the most useful technique in nonograms. Take a clue group and slide it to its leftmost valid position, then to its rightmost valid position. Any cells that are filled in both placements must be filled in the solution.

Example: clue [7] on a 10-cell row. Leftmost position: cells 0 through 6. Rightmost position: cells 3 through 9. The overlap is cells 3 through 6 — those four cells are definitely filled. You can't determine the other cells yet, but you know those four for certain.

The overlap gets bigger as the clue gets longer relative to the line. A clue of [9] on a 10-cell row gives you 8 guaranteed cells. A clue of [3] on the same row gives you none. That's normal — you need other techniques to make progress on short clues.

For multiple groups, the principle is the same: compute the minimum space needed for the group and all groups after it, slide the group within its remaining space, and check for overlap. It gets more complex with multiple groups, but the idea is identical.

Edge logic

When the first cell in a row is known to be filled, the first clue group must start there. If the first clue is [3], fill cells 0, 1, 2 and mark cell 3 as X (the mandatory gap after the group).

The same applies at the right edge for the last group, and at both ends of columns. Edge deductions often trigger a chain: filling a cell at the edge of one line creates a filled cell in the crossing line, which may be on that line's edge too.

X-marking and why it matters

Marking cells with X is just as important as filling cells. An X tells you "this cell is definitely empty," which constrains where groups can go. Every time you place an X, it may reduce the possible positions for a clue group, which may produce a new overlap.

When all groups in a line are satisfied (the filled cells already match the clues), mark every remaining empty cell with X. The auto-strikethrough feature helps you spot these — when a line's clues get a strikethrough, that line is done.

Gap analysis

Once some cells are filled or X-marked, the line breaks into segments. Look at each empty segment between X-marks (or between the edge and the first X). If a segment is shorter than the smallest remaining group, the whole segment must be empty — fill it with X-marks.

If a segment is exactly the size of the next group, the group must go there. Fill it and mark the surrounding cells as X.

Gap analysis gets powerful on 10×10+ grids where earlier deductions create a lot of fragmented segments. It's what turns a half-solved puzzle into a cascade of forced placements.

Cross-referencing rows and columns

Every cell appears in both a row and a column. Filling a cell in one line constrains the other. The standard approach: work through all rows applying overlap and edge logic, then switch to columns and do the same. Each pass fills in more cells, which gives the next pass more to work with.

On hard and expert puzzles, no single row or column may be solvable in isolation. Progress comes from the interplay between rows and columns. You fill a cell in row 4, that cell happens to be in column 7, and column 7's clues now have enough information to determine two more cells. Those two cells feed back into their respective rows. This is the engine that solves large nonograms.

Elimination and contradiction (advanced)

When overlap and cross-referencing don't make progress, you can try hypothetical reasoning. Assume a particular cell is filled (or empty) and trace the consequences. If you hit a contradiction — some line's clues become impossible to satisfy — then your assumption was wrong and the cell must be the opposite.

This is the technique of last resort. On our puzzles, easy through hard levels rarely require it. Expert sometimes does. Einstein puzzles are guaranteed solvable through logic, but the logic may include elimination chains. Our hint system will guide you through them if you get stuck.

What each difficulty level requires

Our five levels scale in both grid size and technique requirements:

• Easy — 5×5 grids, 50–70% filled. Overlap logic handles everything. Great for learning the mechanics.
• Medium — 5×5 to 10×10 grids. Edge logic and X-marking become necessary. Multiple groups per line.
• Hard — 10×10 grids. Gap analysis and row/column cross-referencing are required. Puzzles don't resolve without alternating between rows and columns.
• Expert — 10×10 to 15×15 grids. Dense multi-group clues and multi-step deduction chains. X-marking discipline is critical.
• Einstein — 15×15 grids, logic-only certified. No guessing needed. The hardest nonograms (or picross puzzles, if you prefer) that we offer. Every puzzle is verified solvable through deduction alone.

Quick tips

• Start with the longest clues. A clue of [8] on a 10-cell line gives you 6 guaranteed cells via overlap. A clue of [2] gives you none.
• Always check both the row and the column clues for a cell. One may be ambiguous while the other is definitive.
• Use X-marks liberally. Marking cells as definitely empty is just as valuable as filling them.
• When a line's clues are satisfied (strikethrough), X-mark every remaining empty cell in that line immediately.
• On 10×10+ grids, use the thick gridlines (every 5th line) to orient yourself. It's easy to miscount on larger grids.
• If you're stuck, use the hint system. It points you to one deducible cell and explains the reasoning, which teaches you to spot the pattern yourself.

Putting it together

Start on easy and fill a few 5×5 grids to get comfortable with the interface. Move to medium once overlap logic feels automatic. The hard grids are where the puzzle really opens up — cross-referencing between rows and columns is satisfying once it clicks. And the Einstein puzzles are there for when you want a pure logic workout with no ambiguity.

If you want a deeper walkthrough of the rules, the rules page has step-by-step examples and a FAQ. Or just jump in — you learn faster by doing.

Other grid logic puzzles

If you like nonograms, you might also enjoy these:

• Sudoku — the classic 9×9 number placement puzzle.
• Minesweeper — click to reveal, flag to mark. Uses adjacent-cell counting.
• KenKen — grid puzzles with arithmetic cage constraints.