How to play
The grid holds pairs of numbered ends. Your job is to lay a pipe between the two ends of every pair so that:
- each pipe moves only up, down, left or right, one square at a time,
- pipes never cross or share a square,
- when you are done, every square of the grid is covered by a pipe.
Drag from a numbered end (or from the loose end of a pipe you already started) across the squares you want it to take. Let go and the pipe stays. If a new pipe runs through a square that another pipe already uses, the older pipe is cut just before that square, so you can always draw straight through a mistake and fix the other pipe afterwards. Dragging back along your own pipe shortens it, and tapping a numbered end clears that pipe.
The puzzle counts as solved the moment every pair is connected and no square is left empty. The status line shows how many pipes are complete, how many moves you have made (one move per pipe you draw, change or clear) and the time.
- Undo takes back the last move, one at a time.
- Hint draws one pipe correctly for you. It picks the first pipe that is missing or wrong, and trims any pipe that was in its way.
- New puzzle lets you pick a grid size, or show the solution of the puzzle you are on.
Keyboard: move around the grid with the arrow keys, press Enter or Space on a numbered end to pick up the pen, extend the pipe with the arrows, and press Enter again to put it down. Backspace clears the pipe under the cursor, Escape cancels a pipe you are drawing.
Daily and random puzzles
Daily gives everyone the same puzzle for each grid size, based on the UTC date. A finished daily puzzle stays on the board until the next day. Random generates a fresh puzzle every time you press New puzzle. Both modes save your progress, so you can close the page and continue later.
Grid sizes
| Grid | Pairs |
|---|---|
| 5×5 | 5 to 6 |
| 6×6 | 6 to 8 |
| 7×7 | 7 to 9 |
| 8×8 | 8 to 11 |
| 9×9 | 9 to 13 |
Every puzzle is built by a generator and then checked by a solver: it has exactly one way to connect all pairs while filling the whole grid. If the first layout allows two solutions, the generator splits a pipe into two pairs until only one remains, which is why larger grids have more pairs.
Strategy
Start along the edges. A square on the border can only be entered from three sides, a corner from two. If a corner is empty and only one pipe can reach it, that pipe has to make the detour. Corners are decided first in almost every puzzle.
Look for ends that are boxed in. An end with a single free neighbour has only one way out. Draw that first square immediately; it often forces the next square too.
Think about who fills the gap. Because every square must be covered, an empty pocket between two pipes has to belong to one of them. Ask which pipe can enter the pocket and still reach its own end. Usually only one can.
Pairs that are close rarely take the short route. If two ends sit next to each other, connecting them directly leaves the squares around them for other pipes. Check whether those squares can still be reached by someone else; if not, the short pair has to loop around and take them.
Draw through, then fix. Since a new pipe cuts whatever it crosses, you do not need to clear a wrong pipe first. Lay the pipe you are sure about, then redraw the one that got trimmed.
Use Undo instead of clearing. If a long pipe went wrong three squares ago, undo once and drag again from where it stopped. Starting over costs more moves.
If you enjoy Pipe Flow, try Potion Shelf or Sliding Puzzle next.
