Free Nonogram Solver — Step-by-Step Solutions for Every Grid Size

The Nonogram Solver is a free online tool that processes any Japanese crossword, Griddler, or Picross clue configuration and returns the complete, step-by-step solution path. Available for all nine grid sizes — from 5×5 to 30×30 — the solver applies the same constraint-propagation algorithms and hypothesis-selection strategies used by advanced human solvers, making it both a precise solution tool and an analytical learning resource.

What the Solver Does

The solver accepts a complete set of row and column clues for your chosen grid size and returns:

• The complete solution grid — every cell marked filled or empty

• The step-by-step logical path — which lines were resolved in which order and why

• For Expert through Evil configurations — the hypothesis cell selected, the assumption tested, and the cascade sequence that produced the resolution

• For ambiguous clue sets — an identification of which cells have multiple valid states, rather than an arbitrary selection

This step-by-step output is what distinguishes the solver from a simple answer-lookup tool. The solution path makes the solver a genuine learning resource — solvers who study the path the solver took and compare it to their own approach develop technique faster than those who only check the final answer.

The Solver Algorithm

The solver applies a three-phase algorithm to every configuration, regardless of grid size:

Phase 1 — Initialisation: All valid arrangements are enumerated for every line using a recursive left-to-right block placement algorithm with minimum-gap validation. Initial confirmations (cells whose state is identical across all arrangements for a line) are extracted immediately.

Phase 2 — Constraint propagation: An arc-consistency propagation algorithm processes all lines in a priority queue ordered by ascending arrangement count. Each confirmed cell is immediately applied to all intersecting lines, reducing their arrangement sets and potentially producing further confirmations. This propagation continues until no further confirmations are available through direct deduction.

Phase 3 — Hypothesis resolution: For configurations that resist full propagation, the solver identifies the optimal hypothesis cell using a constraint-graph analysis of the remaining ambiguous network. Both assumption states are traced in parallel; the assumption producing a contradiction confirms the opposite state, which is propagated through the full network. Nested hypothesis trees are handled by recursive application of this process within conditional constraint worlds.

Choose Your Grid Size

Select the solver for your puzzle's grid size:

→ 5×5 Solver | 6×6 Solver | 8×8 Solver

→ 10×10 Solver | 12×12 Solver | 15×15 Solver

→ 20×20 Solver | 25×25 Solver | 30×30 Solver

When to Use the Solver

The solver is most valuable in four contexts:

When blocked on a specific puzzle: You've applied every available technique and cannot identify the next confirmed cell. The solver finds it instantly and explains why it follows from the current constraint state.

When learning hypothesis technique: You're developing hypothesis-and-verify skills and want a concrete benchmark. The solver's hypothesis selection — target cell, assumption, cascade sequence — provides the reference point for evaluating your own approach.

When verifying partial progress: You want to confirm that your current grid state is consistent with the unique solution before investing further time.

When analysing your solving path post-completion: You want to understand whether your completed path was optimal or whether a shorter deductive sequence was available.

Solver Accuracy and Guarantees

The solver is guaranteed to find the unique solution to any well-formed nonogram — a puzzle with exactly one valid cell configuration satisfying all clues. For puzzles with ambiguous clue sets (multiple valid solutions), the solver identifies the ambiguity rather than selecting arbitrarily. All returned solutions are verified against the complete clue set before display.

The solver does not modify your in-progress puzzle session. You can consult the solver at any point and return to your puzzle at exactly the state you left it.

Return to Playing

After reviewing the solver's output, return to the playable puzzles and apply the insights to your next attempt:

→ 5×5 Puzzles · 6×6 Puzzles · 8×8 Puzzles · 10×10 Puzzles · 12×12 Puzzles

→ 15×15 Puzzles · 20×20 Puzzles · 25×25 Puzzles · 30×30 Puzzles