Play, solve, make and print nonograms

Hard Nonogram

Difficult puzzles with one solution that line-by-line logic alone cannot finish.

This free Hard Nonogram tool gives you a random logic puzzle on a grid, set to the hard level, and you solve it right in your browser. The numbers beside each row and column tell you how many filled squares go in that line, and filling the correct squares reveals a pattern.

You can choose a 10x10, 15x15, 20x20 or 25x25 board, with 15x15 as the default. Every puzzle on this page is hard, so line-by-line logic alone will not finish it. You will need to test squares and follow the results. There is no sign-up, and the puzzles are made on your device. Hard puzzles you print here are free to use in products you sell as well, for example in KDP books or Etsy printables.

Hard nonogram example

How to play hard nonograms here

  1. Open the Size menu and choose a board size. The default is 15x15, and 10x10 is the easiest place to start.
  2. Click a square to fill it. To fill several squares in one line, drag across them. The drag stays on the row or column where it started.
  3. Right-click a square to mark it with an X when you know it is empty. Marking empty squares makes the clues easier to read.
  4. Use the arrow keys to move, Space or Enter to fill, X to mark a cross, and Backspace to clear. Press Ctrl+Z (Cmd+Z on Mac) to undo and Shift+Ctrl+Z to redo.
  5. Press Hint when you are stuck. It points to a square that a row or column proves, or says “Try row r, column c” when no single line proves a square.
  6. Press Check to see wrong squares in red, or to see how many squares are still to fill.
  7. Press Show solution only if you want the answer.

On a phone, tap the Fill or X button to choose what a tap does. Use Restart to clear the board and keep the same puzzle, or New puzzle for a new one. The Print button prints the puzzle, and you can tick “Print the answer page too” to add the answer on a second page. Copy link gives you a link that opens exactly the same puzzle.

How to solve hard nonograms

Start by working every row and column line by line, and fill any square that the clue forces. When no line gives a new square, a hard puzzle needs a contradiction test: assume a square is filled, follow the results along its row and column, and see whether a line can still match its clue.

How to start a hard nonogram

Look for clues that force squares right away. If a block of length n sits alone in a line of length L and 2n is greater than L, the middle 2n − L squares must be filled. For example, a clue of 7 in a 10-square row fills squares 4 to 7, because every possible position of that block covers them. A clue of 0 means the whole line is empty, so mark it with X. Then mark the certain empty squares, since they split a line into smaller sections that are easier to read.

Are nonograms hard?

Nonograms are not hard by nature, because each one is solved with logic and counting. The difficulty depends on the puzzle. On easy puzzles, you can solve every line one at a time in at most 3 passes over all rows and columns (4 passes from 20x20), and at least half of all lines give a square on the empty grid. Medium puzzles also solve line by line but need more passes. Hard puzzles get stuck: after every line has been worked, some squares remain undecided.

Do hard nonograms need guessing?

They do not need random guessing, because the next step is a logical test. Pick a square in a long, nearly finished line, where a wrong choice fails quickly. Assume it is filled, follow the consequences along its row and column, and if a line can no longer match its clue, the square must be empty. Then try the opposite choice to confirm it. Every puzzle here has exactly one solution, so you are never choosing between two equally valid answers.

Frequently asked questions

Is the Hard Nonogram tool free, and do I need an account?

Yes, it is free, and there is no sign-up. The puzzles are generated on your device, and nothing is uploaded.

Is my progress saved?

Yes. Progress is saved automatically in your browser and restored when you come back to the page. The timer runs while you play.

Does a hard nonogram have more than one solution?

No. Each puzzle is generated in the browser and kept only after the site’s solver confirms it has exactly one solution.

How does Hint work on a hard puzzle?

Hint shows one square that a row or column already proves. If the square is wrong, it is cleared and pointed out first. When no single line proves a square, Hint suggests a square of the solution instead.

Can I undo a mistake?

Yes. Undo (Ctrl+Z, or Cmd+Z on Mac) steps back one move, and a whole drag counts as one move. Redo (Shift+Ctrl+Z) puts it back.

What does the X mark do?

An X marks a square you know is empty. It is never needed for the solution, but it splits lines into smaller sections and makes the remaining clues easier to place.

Can I sell hard nonogram puzzles made on this page?

Yes. Hard nonogram puzzles from this page are royalty-free for personal, classroom and commercial use, including KDP puzzle books, Etsy and Teachers Pay Teachers listings, and print-on-demand products. No credit is required. The only thing you may not do is copy the generator or the site itself to run a competing service; see the terms.