Nonograms (also known as Picross, Griddlers, or Paint by Numbers) are logic puzzles that reward patience and systematic thinking. Whether you have just discovered these puzzles or want to tackle larger, more complex grids, this guide will walk you through essential techniques — from the basics to advanced strategies that experienced solvers rely on every day.
Before diving into techniques, make sure you understand the fundamentals. A nonogram consists of a rectangular grid with numeric clues along each row and column. Your goal is to fill in certain cells to reveal a hidden picture. Each number in a clue represents a consecutive run of filled cells, and runs must appear in the order given, separated by at least one empty cell.
If you are completely new to nonograms, start with small grids (5x5 or 10x10). These puzzles have fewer possibilities per line, so you can practice the core techniques without feeling overwhelmed. As your confidence grows, work your way up to 15x15, 20x20, and beyond.
A key mindset for nonograms: never guess. Every cell you fill or mark as empty should be justified by logic. If you cannot find a definitive move, keep scanning — there is always a logical step waiting to be found.
Each row and column in a nonogram has a list of numbers that describe the pattern of filled cells in that line. Understanding how to read and interpret these clues is the foundation of solving any nonogram.
Single number clue: A clue of "4" in a 10-cell row means there is one group of exactly 4 consecutive filled cells somewhere in that row, with the remaining 6 cells empty.
Multiple number clue: A clue of "2 3 1" means there are three groups — first a group of 2 filled cells, then a group of 3, then a group of 1 — in that exact order from left to right (or top to bottom for columns). Each group is separated by at least one empty cell.
Empty line: A clue of "0" (or no clue) means the entire line is empty. Mark every cell in that line with X immediately — this is free information.
Full line: If the sum of all numbers in a clue plus the minimum gaps equals the line length, the entire line is determined. For example, "3 4" in a 8-cell row requires 3 + 1 (gap) + 4 = 8 cells, so the placement is fixed: three filled, one empty, four filled.
Complete Filling
When a clue's total (numbers plus minimum gaps) equals the line length, you can fill the entire line immediately. For example, a clue of "5" in a 5-cell row means every cell is filled. A clue of "2 2" in a 5-cell row means the pattern is exactly: filled, filled, empty, filled, filled. Always look for these "freebies" first — they provide guaranteed cells and X marks that help solve intersecting lines.
Overlap Technique (The Most Important Method)
This is the single most powerful technique in nonogram solving. For any clue in a line, imagine sliding the groups as far to the left as possible, then as far to the right as possible. Any cells that are filled in both the leftmost and rightmost positions must be filled in the solution.
Example: A clue of "6" in a 10-cell row. Leftmost placement fills cells 1-6. Rightmost placement fills cells 5-10. Cells 5 and 6 are filled in both cases, so they must be filled. This works with multiple groups too — apply it to each group independently while respecting the positions of other groups.
X Marking (Elimination)
Marking cells as empty (X) is just as important as filling cells. There are several situations where you can confidently place an X:
When a line's clue is fully satisfied (all groups placed), mark every remaining unfilled cell as X. When a filled group is complete (bounded by edges or X marks on both sides and matches a clue number), mark the cells immediately adjacent to it as X. When no group in the clue could possibly reach a cell, mark it as X.
Cross-Reference Analysis
The real power of nonogram solving comes from combining information across rows and columns. When you fill a cell or mark an X in a row, immediately check how that affects the intersecting column — and vice versa. A single cell resolved in one direction often triggers a cascade of deductions in the other direction. Experienced solvers constantly alternate between rows and columns, exploiting every new piece of information.
Edge Solving
When a filled cell touches the edge of the grid (or an X mark), you often know exactly which group it belongs to. If the first cell of a row is filled and the first clue number is 3, then cells 1, 2, and 3 must be filled, and cell 4 must be X. This "anchoring" effect propagates quickly along edges and can solve large sections of the puzzle.
Gap Analysis
Look at the empty spaces between confirmed X marks or edges. If a gap is too small to fit any remaining group, mark the entire gap as X. If a gap can only fit one specific group, you know exactly which group goes there, which often lets you apply the overlap technique within that constrained space for even more precise deductions.
Contradiction Testing
For very difficult puzzles, you can use a trial-and-error approach as a last resort. Assume a cell is filled (or empty) and follow the logical consequences. If you reach a contradiction (a line that cannot satisfy its clue), then your assumption was wrong, and the cell must be the opposite. This technique should be used sparingly — most well-designed puzzles can be solved without it.
Guessing without logic. The most common mistake. Every cell must be justified by deduction. Random guessing leads to cascading errors that are nearly impossible to untangle in larger puzzles.
Forgetting to mark X. Skipping X marks means you lose valuable information. An unmarked empty cell looks identical to an unsolved cell, which leads to confusion and missed deductions.
Miscounting clue groups. Double-check your clue arithmetic. A clue of "3 2" requires a minimum of 6 cells (3 + 1 gap + 2), not 5. Miscounting leads to incorrect placements.
Ignoring intersections. Solving only rows or only columns is inefficient. The power of nonograms lies in cross-referencing. Always check the perpendicular line after making progress on any row or column.
Not verifying completed lines. When you think a line is done, count the groups and compare them to the clue. A misplaced cell early on can corrupt your entire solution if not caught quickly.