Rosehip Reversi

What is reversi?

Reversi is a strategy game for two players on an 8 by 8 board. Every disc is dark on one side and light on the other. You take turns placing discs, and every move flips some of your opponent's discs to your colour. The lead can swing wildly from one move to the next, which is a big part of the fun.

The game was invented in England in the 1880s and has been played around the world ever since. The rules take a minute to learn. Playing it well takes a lot longer, because the player with the most discs halfway through is often the one who is losing. We built Rosehip Reversi to be quick to pick up on a phone, clear to read, and honest about how you played. It's free, it runs in your browser and there's nothing to download.

How to play

1. Setup. The board starts with four discs in the middle: two dark and two light, each pair on a diagonal. Dark moves first.
2. Placing a disc. On your turn, put a disc of your colour on an empty square so that one or more of your opponent's discs sit in a straight line between your new disc and another disc of yours. Lines can run across, up and down, or diagonally.
3. Flipping. Every opposing disc trapped in such a line flips to your colour. If your move traps lines in several directions at once, they all flip.
4. Every move must flip. You can only play where at least one disc flips. In our game, small dots show every square where you can play.
5. Passing. If you have no legal move, you pass and your opponent moves again. You can't pass by choice while you have a move.
6. The end. The game ends when the board is full or when neither player can move.

Winning and scoring

When the game ends, the player with more discs wins. Sometimes a game ends early with empty squares left, for example when one side has been wiped off the board or both sides are stuck. We count those the way tournaments do: the empty squares go to the winner. So a game that stops at 40 to 20 with 4 empty squares is scored 44 to 20. If the discs are level, it's a draw at 32 to 32.

Playing Rosehip Reversi

Tap or click a dotted square to play there. The new disc drops in and the trapped discs turn over one after another, rippling out along each line. With a mouse, hover over a dot first and we show a faint disc there and mark every disc that would flip. A small red mark shows the last move played.

• Undo takes back your last move and the reply, against a house player or in pass and play.
• The light bulb asks our engine for the best move. It rings the square, tells you how the game stands, and names the next best move. Near the end it can tell you exactly what perfect play gives.
• Game review. After a game, our engine looks back over every move where you had a real choice and shows the ones that cost the most, each on a small board with your move and its pick.
• Keys. Tab to the board, then use the arrow keys and Enter to play. H shows a hint, U undoes, P passes and Esc opens the menu. Every square also reads out what is on it for screen readers.
• Settings let you change the flip speed (Normal, Quick or Instant), how fast the house players move, how long Yarrow thinks, and turn off the move dots, the coordinates, hints or undo. Less motion fades discs instead of turning them, and high contrast makes the board bold black and white.

Your game saves as you play. Close the tab, come back later, and Continue puts you back on the same move. Sign in and your games, ladder and looks follow you to any device.

The house players

Five house players, each a step up from the last. They see only the board you see.

We tested the ladder by letting each player face the one below it many times from mixed openings, with the colours swapped on every opening. Each one beat the player below it in at least 4 games out of 5, most of them in more than 9 out of 10. Our engine is our own: it counts mobility, corners, the risky squares beside them, edges and parity, and its weights were tuned on thousands of games it played against itself.

Daily Opening and the ladder

The Daily Opening is one game against Burdock, the same for everyone on the day. A few opening moves are already on the board, chosen so that neither side has the edge, and you take over the side to move. Your score is your number of discs at the end, out of 64, with the empty squares going to the winner. 33 or more is a win. Burdock always answers the same way to the same moves, so everyone faces exactly the same opponent.

Your first game of the day goes on the daily leaderboard. You can play it again just for fun, but only the first one counts. There are no hints and no undo in the daily. A new opening arrives at midnight UTC, and a streak builds when you play on consecutive days.

The ladder is a rating that starts at 1200 and moves after every game against a house player. Beat a stronger player and it climbs more. The ladder board keeps your best.

Play with friends

Pass and play lets two people share one phone, tablet or computer. The first name plays dark. Play a friend is online: one of you hosts and gets a four letter room code, the other types it in or opens the shared link. No account needed. Colours are picked at random for the first game and swap on every rematch, and you can send a quick reaction. Online games never post to the leaderboards.

Tips and strategy

Corners first

A disc in a corner can never be flipped, and it anchors the edges next to it. Taking a corner is usually a big step toward winning, and giving one away is usually a big step toward losing.

Beware the squares beside an empty corner

The squares diagonally next to a corner (b2, g2, b7 and g7) are the most dangerous on the board while that corner is empty, because they often let your opponent take it. The edge squares right beside a corner are risky too. Once the corner is filled, they're safe.

More moves beats more discs

Early on, the number of discs barely matters. What matters is mobility: how many moves you have compared with your opponent. Aim to leave yourself plenty of choices and your opponent few, so that sooner or later they have to play somewhere they don't want to. A player with very few discs in the middle game is often doing well.

Play quiet moves

Good moves flip a few discs, ideally ones inside your group, and don't add new discs next to empty squares. Every disc you put on the edge of the crowd gives your opponent something to flip and somewhere to play.

Count the regions at the end

Near the end, the empty squares split into small regions. Try to get the last move in each one. As a rule of thumb, it's good to be the one who moves into a region with an odd number of empty squares.

Use the review

After a game, open the review. Most games are lost by two or three moves, and seeing them on the board with the better choice next to them is the quickest way we know to improve.

Questions