15 Puzzle

How to play 15 Puzzle

Slide the numbered tiles into ascending order, reading left to right and top to bottom, with the empty gap in the bottom-right corner. The classic board is 4 × 4, with fifteen tiles. The optional 3 × 3 and 5 × 5 boards use the same rules with eight and twenty-four tiles.

Slide a tile or a whole line

A tile may slide horizontally or vertically into the gap. Tap any tile in the gap's row or column to shift the intervening line. Each individual tile moved counts as one move: sliding three aligned tiles adds three moves. A tile in a different row and column cannot move. There are no diagonal moves, arbitrary swaps or time-limit losses.

On a phone, tap a tile or swipe straight across the board. Swipes move the gap in the direction you swipe, one square at a time. The arrow buttons and keyboard arrow keys move the gap in the same way. Enter or Space slides the focused tile. U undoes the previous whole slide, R redoes it, H requests a hint, and P pauses. Cancelled gestures and releases outside the board leave the tiles unchanged. Scroll the page from outside the board.

Classic and Gentle shuffles

Every starting board is created by legal slides from the solved board, checked for the correct solvability parity, and kept unsolved. Classic shuffle uses a longer random walk; Gentle shuffle uses fewer scrambling moves. The shuffle length is not the minimum solution length, a human difficulty grade or an optimal-move target. Either style can have shorter routes than the scramble's return path.

A useful route hint

Hint highlights one adjacent tile that can follow a verified legal route toward the ordered board. It retraces the scrambling path and your subsequent moves as needed, removing immediate backtracks. This route can revisit positions and is not promised to be shortest. The tile does not move automatically; tap it when you are ready. No expensive optimal-solution search runs on your phone.

Hint requests, Undo use and Restart are recorded for the whole attempt. Redo, reloading or returning the tiles to an earlier position cannot remove that assistance. Restart returns to the same starting arrangement and resets the active clock, while keeping the same attempt and its assistance. New puzzle creates a fresh attempt.

Save, pause and personal bests

Your board, move count, up to 200 undoable slide gestures, hints, active time, achievements and best records save in this browser when storage is available. The clock starts on your first legal slide or hint. It pauses when you open a dialog or leave the tab; an unfinished saved puzzle waits for Resume. Full screen keeps the tiles and controls together, and Back or Escape restores the page. Sound starts off and celebrations respect reduced motion.

Best time and fewest moves are tracked separately for each board size and shuffle style. Only an attempt's first completion without Hint, Undo or Restart qualifies for a record. Assisted or restarted completions are practice results; they still count as a real puzzle completion once for that attempt. Reviewing, Undo/Redo, restarting and reloading never duplicate a completed attempt or improve its original record. A visible message explains when saving is unavailable.

Eight little milestones

Earn stars for your first slide, putting the top row in order, placing half the numbered tiles at home, finishing a puzzle, finishing the classic 4 × 4 board on Classic shuffle, finishing a 5 × 5 board, completing without Hint/Undo/Restart, and completing three different attempts. Stars stay in a reserved strip below the board, so the celebration never hides a number.