Tap an arrow, it slides one step. Clear the whole board.
Every tile on the board is an arrow pointing up, down, left or right. Tap one and it slides a single square in the direction it is pointing. If the square ahead already has an arrow in it, nothing happens — that arrow is blocked until the one in front of it moves out of the way. When an arrow slides off the edge of the board, it is gone. Clear every arrow and the level is done.
That is the entire rule set. The difficulty comes from order: the same board can be trivially easy or completely stuck depending on which arrow you free first.
Beginners clear the easiest arrows first — the ones already touching an edge, pointing outward. It feels like progress, and it is exactly how you get stuck. Those arrows were the ones that could have moved aside later to let a trapped arrow through. Once they are gone, the arrow buried in the middle has nowhere to go.
A better habit: look for the arrows with the longest journey ahead of them and ask what has to clear out of their path. Work backwards from the hardest one instead of forwards from the easiest.
Two arrows facing each other with no space between them can never move again. Neither can a ring of arrows all pointing into the same closed loop. These are permanent — no sequence of taps will fix them. If you see one forming, undo immediately rather than playing on and hoping.
Undo is unlimited and free. Restart is always available. There is no penalty for either beyond the star rating, and a two-star finish is still a finish.
The minimum is not a guess. Every level is built by working backwards from a solved board, so the exact shortest solution is known before you ever see it. That is also why no level here can be impossible — a solution exists by construction.
The board starts at four by four and grows to seven by seven. The number of arrows grows with it, and so does the amount of tangling — later levels place arrows deep inside the board with several others sitting in their path. Level 50 has arrows that need most of the board cleared before they can even start moving.
Each level is the same for everyone. Level 23 on your phone is the same board as level 23 on anyone else's, so a friend who says a level is hard is talking about the same puzzle you are looking at.
Your progress, your stars and your day streak live in your own browser. There is no account and nothing is sent to a server. Clearing your browser data clears them too.