Reversi, also called 翻转棋, is played on an 8×8 board of 64 squares with four discs already placed in the middle. Black moves first and the two sides alternate. This is a pure front-end version: it opens and plays immediately, with no sign-up and no download. A move is a single tap — the squares you may legally play light up, and when you place a disc, every opposing disc trapped between it and another of your discs flips over. All eight directions settle independently, not just the longest run. A square that would flip nothing is not a legal move, so the highlighted squares are the complete list of your options. If it is your turn and nothing is highlighted, your turn is skipped automatically; when neither side can move the game ends and whoever has more discs on the board wins.

The flipping is the whole game. Plastic discs, red on one face and black on the other, pinched at the edge and turned over one at a time — click, click, click — and when the run is long enough you never want it to stop. The board was folded card with a crease down the middle that always trapped a disc or two. Set it up at break, snap it shut when the bell goes, discs rattling back into the bag, and pick it up again next break with nobody ever forgetting which side they were. This version keeps the paper, the crease and the rhythm of that run of flips.

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【纸】 Pen, paper and the desk drawer · 全程 →

1. 01

   The board is already set up with four discs in the middle — tap Start, or just tap the board, to begin.

2. 02

   Playable squares light up. Tap one and the disc is placed; there is no second confirmation, no dragging and no long press.

3. 03

   Every opposing disc caught between your new disc and another of your own flips over, with all eight directions settling at once.

4. 04

   Tapping a square that would flip nothing is refused — the status line says so, and neither the board nor the move count changes.

5. 05

   If it is your turn and nothing is highlighted, the turn is skipped for you automatically and the status line explains why.

6. 06

   Tap Undo to take a move back. There is no limit, not even at Expert; it is only greyed out while the opponent is thinking.

7. 07

   The page never freezes while the AI thinks — the board still answers taps, and a long search just adds one line to the status bar.

8. 08

   On desktop, arrow keys move the cursor, Enter places, U takes back, and Esc or P pauses. On touch, everything is a single tap.

The classic beginner mistake in Reversi is taking the move that flips the most discs every time — the built-in Starter tier plays exactly that way, which is why it is beatable. Flipping a lot in the midgame leaves your discs spread across the lines your opponent is about to play through, and they come straight back. The number worth watching is the safe count next to the board: it only ever rises, so it reads your position far more honestly than the disc count. A rough order of priority: take a corner whenever you can; when you cannot, avoid the square diagonally inside an empty corner, because the disc you place there is what lets your opponent reach that corner; otherwise prefer moves that keep your own options open while shrinking your opponent's, so they are left playing only the squares you want them to. And if you misplay, take it back — undo has no limit.

How do you play Reversi? Are the rules complicated?

There is really one rule: trap your opponent's discs and they flip. From the square you play, look along each of the eight directions — if a run of opposing discs is closed off by one of your own, that whole run becomes your colour. The squares you may legally play are highlighted for you, so there is nothing to calculate. At the end, whoever has more discs wins.

Why can't I play on some empty squares?

Because that move would flip nothing. In Reversi a zero-flip move is illegal — there is no option to place a disc without capturing — so an empty square is not automatically playable. The page highlights the squares that genuinely work, and tapping elsewhere leaves the board and the move count unchanged.

What happens when I have no legal move?

Your turn is skipped automatically and you do not have to tap anything. The rule is that when one side has no legal square and the other does, play passes straight back, and this can happen several turns in a row. Note that passing is neither a penalty nor something you can choose — leaving your opponent with no move is exactly what you want in the late midgame.

The game ended before the board was full. Who wins?

Whoever has more discs. The game ends as soon as neither side has a legal move, which can happen with empty squares still on the board — for example when one side has had every disc flipped. Full board or not, the result is decided the same way: count the discs at the end, most wins, equal draws.

How many AI levels are there, and why is Starter easy to beat?

Three: Starter, Advanced and Expert. Starter is deliberately weak — it only asks how many discs a move flips right now, so it values corners and edges no more than anything else and will happily let you take all four corners. Advanced and Expert weigh corners, safe discs and how many options you have left, with Expert searching hundreds of thousands of positions per move. You pick the tier in the opening panel and it applies to the next game.

Can two people play on one device?

Yes — switch Mode to two players in the opening panel. You take turns on the same screen and the board never rotates; the turn marker on the disc counter shows whose move it is. Two-player games are not scored, so the score stays at 0 by design rather than by fault.