Mosaic Puzzle Generator

Mosaic is minesweeper turned inside out: instead of avoiding the shaded squares you are trying to find them. Each printed number counts the shaded squares in the block of nine made up of that square and the eight around it, itself included. Every grid here has had numbers removed one at a time, each removal kept only while a single answer survives.

Grid

Picture

Seed (optional)

The same seed rebuilds the same puzzle. Deterministic, not cryptographic.

A grid scattered with numbers, each counting the shaded squares around it, will appear here.

What this generator does

Shades a grid at random, numbers every square with the count of shaded squares around it, then takes numbers away one at a time — keeping a removal only while the numbers that remain still lead to a single answer.

How to use this tool

Choose a grid size and how full the finished picture should be.
Print or copy the grid — the numbers stay where they are as you shade.
Start with the 0s and the 9s: they settle their whole block at a stroke.
Work outwards by comparing blocks that overlap, which is where the puzzle lives.
Show the answer to check the finished picture.

Understanding the controls

Grid: Seven to ten squares a side. Ten is the ceiling because the removal pass runs a full solve for every square, and a twelve-by-twelve measured eighteen seconds a puzzle.
Picture: Roughly how much of the finished grid is shaded. An airy setting gives lower numbers and more white space; a solid one gives higher numbers and a denser picture.
Seed (optional): Type anything to rebuild the same puzzle later, which is how you reprint a page you have lost. Deterministic, not cryptographic.

Common use cases

A longer sitting than a sudoku, with a picture at the end of it
A printable puzzle page for a club, a newsletter or a classroom
Practice at counting and reasoning together, for anyone who likes minesweeper
A puzzle to solve on paper away from a screen
Reprinting the identical grid later from its seed

How this generator works

Uniqueness is proved from the printed numbers alone. Everything the numbers force is settled first — a block that already has all the shading it wants leaves the rest of itself blank, and a block that needs every square still undecided fills them all — and only then is a square guessed, always the one in the tightest block. Numbers are then removed one at a time and a removal is kept only while a single answer survives. Numbering every square is not by itself enough, which was worth learning: of fifteen eight-by-eight grids tried, five had a second shading that satisfied all sixty-four numbers, so a grid like that is discarded before any number is removed.

Randomness and fairness

The shading, and so every number on the page, comes from your browser's cryptographic random source unless you give a seed — a seeded puzzle is deterministic, not cryptographic.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

Ten squares a side is the ceiling. Past it the work of proving a single answer climbs steeply enough to be worth refusing rather than making you wait.
The picture is random rather than a recognisable image, so the finished shading is abstract.
Difficulty is not graded. Some grids give a clue that decides its whole neighbourhood at once; others need several counted against each other first.
About two squares in five keep a number, which varies from grid to grid.

Privacy and your data

The grid is shaded, numbered and checked entirely in your browser. Nothing you type as a seed, and no puzzle made from it, leaves the device.