Think with the empty square.
A practical guide to the eight tiles, the gap and the move you can undo.
The target arrangement
Read the board left to right, top to bottom: 1 through 8, followed by an empty lower-right square. This is the solved state. No minimum move count is required.
A shared edge is enough
Only a tile directly above, below, left or right of the gap can slide into it. A diagonal or distant tile cannot move in one step. With keyboard focus on the board, the arrow keys move the gap.
Undo an experiment
Undo returns to the preceding arrangement and removes that move from the counter. Use it to compare two options. A new puzzle clears the history rather than saving earlier attempts.
Why the shuffle has a route back
The board is mixed using legal moves from the solved state. That gives it a reachable solution. Work a section at a time, or stop and begin another board; nothing is purchased or redeemed when you finish.
Only a neighbouring tile can slide.
Worked example · not your current boardTry Jelly Shift
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