How to Solve Fillomino: Walls, Sealed Cells and Faster Times

Updated October 2026

Fillomino is a region-growing puzzle: every cell gets a number, and every group of equal, edge-connected numbers must be exactly as large as the number it holds. The rule fits in one sentence, but solving quickly takes a handful of reliable deductions. This guide covers the specific puzzles this site generates, the techniques that crack them, and the habits that cut your clear time, since the leaderboard ranks the fastest solves.

What the puzzles here look like

Every puzzle is a 6×6 grid, and the number pad under the board offers only 1 to 5. That limit is real information: no block in the solution is ever larger than five cells, so an empty area of the board can never be filled by one big region.

Puzzles are made by cutting the grid into random blocks and then removing given numbers one at a time, checking after each removal that the puzzle still has exactly one solution. In our simulation of 300 generated puzzles, the starting grid kept a median of 14 given numbers (between 11 and 19), and the solution contained a median of 13 blocks. Small blocks are the most common: about 28 percent of all blocks were single cells, 22 percent were twos, 18 percent threes, 16 percent fours and 14 percent fives.

The generator does not promise that every block shows at least one of its numbers. In the same simulation, about a third of the single-cell blocks and about a fifth of the two-cell blocks had no given number at all, while blocks of five almost always kept one. When you meet an empty pocket with no clue nearby, the answer is usually a small block.

Controls and feedback

Choose a number on the pad, then tap a cell to write it or drag across several cells to write the same number into all of them. The selected key stays active until you choose another, so you can fill a whole block in one sweep. The ⌫ key works the same way as an eraser brush. Given numbers are drawn brighter and cannot be changed.

Every cell you fill is tinted by the state of its block. A block whose size equals its number turns green; one that has grown too big turns red; one that is still short stays neutral. Heavy lines are drawn wherever two neighbouring cells hold different numbers, so the shape of each block is visible at a glance. The puzzle ends the moment every cell is filled and every block is exactly the right size.

The core deductions

Finished blocks build walls. As soon as a block is complete, every empty cell touching it must hold a different number, because an equal number would join it and make it too big. A finished 1 means none of its neighbours is a 1; a finished 3 means none of its neighbours is a 3.

Sealed single cells are 1s. If an empty cell is surrounded on every side by edges or by finished blocks, it cannot grow, so it must be a block of size 1. That only works if none of the finished neighbours is itself a 1; if one is, look again, because you have made an error somewhere.

Count the room a clue has. A given 4 needs three more cells. Count the empty cells it can reach without passing through a different number. If exactly three are reachable, they are all 4s. If more are reachable but every route passes through one particular cell, that cell is a 4.

Watch for clashes between equal clues. Two given 3s two cells apart cannot both grow toward each other, because if they met they would form one block of at least six. Often the cell between them must hold a different number, which in turn tells you how each of them grows.

Split sealed areas by size. When a group of empty cells is closed off by finished blocks and edges, its cells must form complete blocks of their own. A closed area of two cells is either a 2 or two 1s; two 1s side by side would merge, so it must be a 2. Use the same counting on larger pockets, remembering that no block can exceed five and no two blocks of the same size can touch.

Where to start

Begin with the clues that have the least freedom. Look for given numbers that are already complete as printed, such as a lone 1 or a pair of adjacent 2s, and mark their walls mentally. Then look at clues jammed against the edge or a corner, since their reachable area is small. Large clues in the open centre are the least constrained and are usually best left for later, when the cells around them have been decided.

A cell in a corner is not automatically small. Even if it has only one empty neighbour, it can still be part of a large block that grows out through that neighbour. Corners help because they reduce the number of directions, not because they cap the size.

Reading colours to catch mistakes

Red is the fastest warning in the game: a red block is definitely wrong and should be fixed right away. Green is weaker evidence. A block can be the correct size and still be the wrong shape, so a green block is only safe once the cells around it make sense too. If you finish the grid and nothing happens, some block is the wrong size: look for red, and for neutral tints, which mark blocks that have not reached their number yet. Two equal blocks that touch simply merge into one oversized red block.

Because only one solution exists, every cell has one correct value. If you find yourself choosing between two options with no reason to prefer either, stop and look elsewhere. There is always a deduction available, often around a clue with only one way left to grow.

Shaving seconds off your time

The clock starts when you press Start on the Ready card, not when the page loads, and stops the moment the last correct number goes in. It runs on real time, so leaving the tab or locking the phone does not pause it. Times are rounded to whole seconds, your best time is stored on this device, and every solve can be submitted to the Hall of Fame.

• Drag whole blocks. Once you know a block, select its number and sweep across it in one stroke instead of tapping each cell.
• Batch by number. Switching keys costs a tap each time. When several blocks of the same size are known, fill them all before changing the brush.
• Leave easy fills for last. Sealed 1s and closed pairs are quick to write; solve the board in your head first and write those in a single pass at the end.
• Erase with the brush. The eraser works by dragging too, which is faster than painting over cells one by one.