Region Tetromino Puzzle Generator
A region tetromino puzzle cuts the grid into irregular blocks, each a little bigger than four squares, and gives no numbers at all — the block shapes are the only clue there is. Inside every region, exactly four squares are shaded, and those four must form one of four tetromino shapes: a straight line, a T, an S or Z, or an L or J — never a two-by-two square, and never four squares that do not connect to each other. Two regions that touch may not shade the same shape, no two-by-two block anywhere may end up entirely shaded, and every shaded square across the whole grid must connect to every other through shaded squares. Every grid here is checked to have one answer and no other.
What this generator does
Grows the grid's regions as random connected blocks, folds any stray region too small for a tetromino into a neighbour, draws one genuine random shading that obeys every rule as it goes rather than checking afterwards, then proves by exhaustive search that the region shapes alone allow exactly one shading before publishing.
How to use this tool
- Choose a grid size, then print or copy it — the thicker lines mark region walls.
- Shade exactly four squares in every region, forming a straight line, a T, an S/Z or an L/J shape.
- Never shade a two-by-two square, and never let two touching regions share the same shape.
- Keep every shaded square connected to every other shaded square in the grid.
- Show the answer to check the finished grid and see which shape each region used.
Understanding the controls
- Grid
- Six or seven squares a side. With no numbers to lean on, a seven-square grid needs many more candidate layouts tried per puzzle than six does, which is why it stops there.
- Seed (optional)
- Type anything to rebuild the same puzzle later, which is how you reprint a page you have lost. The seed makes the puzzle repeatable; it carries no cryptographic strength and is not a secret.
Common use cases
- A shading puzzle where the regions themselves are the only clue
- A printable page for solvers who already know the four tetromino shapes, since nothing on the grid names them
- A step up from a numbered shading puzzle for a confident solver
- A companion to a room shading puzzle for anyone who wants the harder, clueless version
- Reprinting the identical grid later from its seed
How this generator works
This puzzle carries no numeric clue anywhere, which removes a repair trick the site's other shading puzzles rely on: when one of those finds an ambiguous answer, it can turn a disputed square into a clue and try again. Here the region shapes are the whole of what is given, so an ambiguous layout cannot be patched — it can only be discarded for a fresh one. Measured directly, that turned out to be the binding constraint: at five-to-eight-cell regions, not one of sixty random layouts came out uniquely solvable; shrinking the regions to five-to-seven cells raised that to roughly one layout in thirty. At that rate the generator tries many candidate layouts, once each, rather than persisting with one. Drawing the shading itself has the same story as this site's other room-based puzzle: chosen independently per region and checked afterwards, it essentially never keeps every rule at once, so instead one search settles every region in a shuffled order, trying each region's own shuffled list of valid tetromino placements and pruning the moment two touching regions would share a shape or a two-by-two block would fill in — with only the whole-grid connectivity rule left to check on a finished layout, since a cut-off pocket of shaded squares cannot be told apart from a merely-not-yet-joined one any earlier.
Randomness and fairness
The region layout and the shading both come from your browser's cryptographic random source. Giving a seed replaces that source with a repeatable one, so the same puzzle can be printed again; the seed is for reproducibility, not cryptographic strength.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- The grid stops at seven squares a side — a measured limit: an eight-square grid needed a much larger region size to stay solvable at all, and even then was noticeably less reliable and slower to build than seven.
- There is no numbered clue anywhere, by the rules of the puzzle itself, so there is no way to make one region individually easier the way a numbered shading puzzle can.
- Difficulty is not graded. A grid can be led by its region shapes from the first move, or need a section worked out before it opens up.
- Regions are grown to between five and seven squares, but merging strays makes some larger, occasionally ten squares or more, and a region can occasionally end up exactly four squares, which removes any internal choice for that one region alone.
Privacy and your data
The region layout, the shading and the check that it is unique are all done entirely in your browser. Nothing you type as a seed, and no puzzle made from it, leaves the device.
Related generators
- Room Shading Puzzle GeneratorPrints a grid cut into numbered rooms — shade each room to its count, keep the rest connected, and never let a straight run of unshaded squares cross three rooms — with exactly one answer.
- Pentomino Tiling Puzzle GeneratorFit all twelve pentominoes onto a sixty-square board, each used exactly once, from two or three pieces already placed (occasionally one or four) — with exactly one way to finish.
- Stitches Puzzle GeneratorA grid cut into blocks, to be sewn together: one stitch across every border between two blocks, with the number of holes in each row and column given — and exactly one way to do it.
- Tapa Puzzle GeneratorPrints a Tapa grid where each clue counts the runs of shaded squares around it, with exactly one wall that fits.
- Shikaku Puzzle GeneratorCut the grid into rectangles, one number in each, that number being its area — with the single answer proved before you see it.
- Nurikabe Puzzle GeneratorNurikabe grids where each number is an island of that size, the wall is one piece, and no two-by-two block is allowed.