Zip Puzzle — Complete Rules and Strategy Guide
The Zip puzzle is a pure path-deduction game built on a classic graph problem called the Hamiltonian path. You get a grid of cells, a start square marked 1, a finish square marked with the highest number, a handful of checkpoints in between, and a scattering of walls that block movement between neighbouring cells. Your job is to draw one single unbroken line that begins at 1, passes through every cell exactly once, hits every numbered checkpoint in strict order, and finishes on the last number. Because the line can never branch or cross itself, every move you make is a commitment — which is exactly what makes the Zip puzzle so satisfying.
Zip Rules in Five Lines
- One path only. Your line is a single strand. It never branches, crosses or touches itself.
- Every cell exactly once. On an n×n board the path passes through all n² cells, one visit each.
- Checkpoints in order. The path must reach 1, then 2, then 3 and so on up to the final number.
- Walls block. A thick wall between two cells means the path cannot travel directly between them. Diagonal movement is never allowed.
- Orthogonal steps only. The path moves up, down, left or right — never diagonally, never across a wall.
How the Zip Generator Works
Every Zip board is generated in your browser the moment you press play — there is no puzzle bank and no server call. The generator picks a random start cell and then walks a Hamiltonian path using Warnsdorff's heuristic: at every step it prefers the neighbour with the fewest onward options, with a random tie-break so that different seeds produce different routes. Checkpoints are then stamped onto the path in ascending order and walls are placed on edges the path does not use, so no wall can ever block the real solution. Finally an independent depth-first solver counts the number of valid completions of the resulting board. If that count is anything other than one, the board is rejected and generated again — you will never be handed a Zip puzzle with two answers or none.
Choosing Your Grid Size
Unlimited mode offers 5×5 up to 9×9 boards. A 5×5 Zip puzzle is a 25-cell sprint you can finish in under a minute, ideal for learning how walls and dead ends interact. At 7×7 and 8×8 you will need to build the path from both ends and keep careful count of the remaining cells. A 9×9 board has 81 cells and is a genuine test of patience and spatial memory — save those for when the smaller sizes feel routine. The daily Zip puzzle is seeded from the calendar date, so every player in the world gets the identical board on the same day.
Advanced Zip Tactics
- Chain the checkpoints first. Work out the shortest legal route between consecutive numbers before you draw anything; if two numbers sit near opposite corners, the path between them is largely forced.
- Respect degree-one cells. A cell with a wall on three sides has a single neighbour. That cell must be an endpoint of the whole path or it will strand itself.
- Check connectivity constantly. Before confirming a move, glance at the unvisited cells: if your path has split the board into two separate pockets, undo immediately.
- Retract with a tap. Tapping the current head of your path steps it back one cell, so experimenting is free. Treat undo as a thinking tool, not a failure.
- Use walls as positive information. A wall placement is the generator telling you the path does not run there — read the remaining gaps as the only legal corridors.
Why Play the Zip Puzzle Unlimited?
One Zip puzzle a day is a lovely ritual but a poor teacher. Unlimited mode turns the Zip puzzle game into a practice range: pick a size, press New Puzzle, and work a brand-new board with fresh walls and a fresh checkpoint layout. The deduction muscles you build on 25-cell boards transfer directly to the daily Zip puzzle, which is shared by every player on the same date. Everything here is free, needs no account, and every generated board is verified to have exactly one solution before it reaches your screen.
