LOGIC PUZZLE
Filo: numbers in order
One single thread. It starts at 1, touches the numbers in ascending order and must fill every square of the grid, never crossing itself, ending on the last number. Every grid has exactly one solution — verified by a solver, not promised. Plays free in the browser, no sign-up.
Drag from dot 1 to draw the thread. Moving back onto an earlier square shortens the thread to that point. «Clear» starts over from the beginning.
How to play
The grid holds numbers from 1 upwards. Draw a single path that starts at 1, passes through 2, then 3, and so on to the last number — touching every square of the grid exactly once. The thread moves horizontally and vertically, never diagonally, and cannot revisit a square.
The two requirements constrain each other: reaching the last number is not enough, you must arrive having consumed the whole grid. That is where the puzzle gets interesting.
Three ways to reason
Corners rule
A corner square has only two neighbours: the thread can only enter through one and leave through the other. If a square next to the corner is already taken, the corner risks becoming a dead end — and a dead end that is not the final number means starting over.
Never cut the grid in two
Every stretch of thread is a wall. If your path splits the remaining squares into two islands, the game is already lost: there is one thread and it cannot jump. Before any long move, look at what is left on either side.
Look one number ahead, and one more
Between a number and the next one, the thread has to consume the squares that would otherwise be orphaned. If 4 sits close to 5 with half an empty grid around them, the right route between the two is almost never the direct one: it is the detour that sweeps the area clean.
The options
- Size — 5×5, 6×6 or 7×7.
- Hints — a hint keeps the correct stretch of your thread, cuts the wrong one and extends it to the next number.
- Resume — the game saves itself: close the tab and find it where you left it.
Frequently asked questions
Is this like LinkedIn's Zip?
Same puzzle genre: a single path touching the numbers in order while filling the grid. This version is independent, needs no account and generates fresh grids endlessly, always with a unique solution.
Is the solution really unique?
Yes, and it is verified rather than claimed: a solver counts the valid paths of every grid before it is served. If two exist, the grid gets one more number or is discarded. An ambiguous grid never reaches you.
Is it free?
Yes, it plays free in your browser. No sign-up, no advertising, no data collection: the whole game runs on your device.
Does it work on a phone?
Yes: you drag your finger to draw the thread, and the buttons at the bottom adjust the zoom or fit the grid to the screen. Fullscreen is there too.
Is progress saved?
Yes. The game in progress is kept in your browser's local storage, so you can close the tab and pick up where you left off. The save never leaves your device and is dropped once the game ends.
How it is built
The problem is the inverse of what it looks like. You do not generate a single-solution grid by searching for the solution: you build it.
The path comes first: a serpentine covering the grid is scrambled hundreds of times with the «backbite» transformation — fold one end onto an inner square and reverse the stretch beyond the fold. The result still touches every square exactly once, but is unrecognisable. Then come the numbers: initially just the first and the last, and a solver counts how many valid paths the grid admits. If it finds more than one, a new number lands in the middle of the widest gap and the count runs again — until exactly one solution remains. The numbers you see are the bare minimum that keeps the puzzle honest.
It comes out of the same way of working I apply to products: Miraviso is a real case, and if you need a hand with something similar, start here.