Universal Reversi is a two-color disc game where one move can turn a whole row of enemy pieces into your own. The catch is the board itself: it loops like an old arcade screen, so a line that runs off one side carries on from the opposite side. You can play Universal Reversi unblocked against a friend on one screen or against a computer that ranges from relaxed to sharp. Norbert Nopper built it as a single self-contained web page.
How to Play Universal Reversi
Every game starts with four discs in the middle, two black and two white, set on the diagonals. Black moves first unless you change the starting color.
On your turn, place a disc on an empty square so that one or more of your opponent’s discs sit in a straight line between the new disc and a disc you already own. All of those trapped discs flip to your color. Lines can run in any of the eight directions, including diagonals, and one placement can flip several lines at once.
Here is what makes this version different. When a line reaches the border, it does not stop. It continues on the far side of the board, both left-right and top-bottom. A disc on the right edge can therefore be flanked by a disc on the left edge.
A few more rules round it out:
- Small dots show every legal square for the player whose turn it is. You can only click a dotted square.
- If you have no legal move, your turn is skipped and a message says the other side plays again.
- When neither player can move, the game ends. The side with more discs wins, and equal counts end in a tie.
- The score boxes at the top count each color’s discs after every move, and the last placed disc is highlighted.
Your First Game, Step by Step
The default setup puts you on Black against the computer on an 8x8 board at Medium. Press Reset Game if you want to start fresh.
Look at the four center discs and the dots around them. In the opening, every legal move flips exactly one disc, so the choice is about position, not points. Pick one and watch the computer answer after about a second.
After a few turns, try the PAN arrows below the board or the arrow keys. Each press shifts the view one row or column, and the discs slide around as if the board were printed on a ring. Pan until the cluster of discs sits near an edge and you will see how a “border” square is really surrounded on all sides. That habit of panning is the main new skill this game asks of you.
Settings and Game Modes
The Game Settings panel controls the match itself. Changes there only apply after you press Reset Game.
- Players: Human vs Human, Human vs AI, AI vs Human, or AI vs AI. The first name in each pair plays Black.
- Starting color: Black or White can make the first move.
- Board size: a slider with three steps: 6x6, 8x8 and 10x10.
- AI difficulty: Very Easy, Easy, Medium, Hard and Extra Hard.
The Runtime Settings panel changes things in the middle of a game. The AI response delay runs from 0.02 seconds up to 2 seconds, with 1 second as the default. You can also switch the legal-move dots off for a harder game, turn the flip animations off, and turn on an accessibility mode. That mode swaps the shaded discs for flat black and white ones, each with a bold contrasting ring, so the two colors are easier to tell apart.
AI vs AI is worth a look. Set both sides to Extra Hard with a long delay and you get a slow demo of how the board wraps and how strong moves look.
How the Computer Thinks
Knowing how each level picks moves helps you beat it:
- Very Easy chooses any legal move at random.
- Easy always takes the move that flips the most discs right now. It never thinks about what you do next, so you can bait it with big but weak captures.
- Medium, Hard and Extra Hard search ahead one, two and three replies deep.
The deeper levels judge a position in two stages. While the board is mostly empty, they care about mobility: having more legal moves than you. As the board fills, they shift toward simply counting discs. That is a strong plan, and it is worth copying.
Universal Reversi Tips and Strategy
Classic advice says to grab corners because they can never be flipped. On a wrapped board, there are no true corners, so that advice falls apart. Try these ideas instead:
- Count options, not discs. Early on, a move that leaves you many choices and your opponent few is better than one that flips a lot.
- Pan before you commit. Scroll the view so the line you are checking sits in the middle of the screen. Wrapped lines are easy to miss at the edge.
- Avoid long single lines of your color. A straight run of your discs can be flipped in one shot from either end, and on this board both ends are always reachable.
- Watch the pass message. Forcing your opponent to skip a turn lets you move twice in a row, which is huge late in the game.
- Save the big flips for last. Disc count only matters at the end, so take the large captures in the final dozen moves.
- Read the computer’s dots. The move dots stay visible while the computer is thinking, so you can see every square it might choose.
Mistakes New Players Make
The most common slip is forgetting the wrap. A disc you thought was safe on the left edge gets flipped from the right side, and suddenly half a row changes color.
Another is playing greedily like the Easy bot. Flipping eight discs feels great, but it often opens many new squares for the other side. Last, many players change a setting and expect it to work right away. Remember that board size, players and difficulty all wait for Reset Game.
Playing on a Phone or Chromebook
On a Chromebook or laptop, click a dotted square to play and use the arrow keys to pan. On a phone, the board and panels stack in a tall layout, so it plays well held upright, and the rules section folds away to save space. The board squares shrink to fit the screen, which keeps even 10x10 readable. There is no sound, so it suits a quiet classroom.
Similar Games on Totally Science
If you like flipping and surrounding, try Gomoku, where you race to line up five stones instead of flipping them. Checkers is a good pick if you want pieces that move and capture by jumping. For a short two-player match with gravity, Four in a Row is quick to learn. You can find more on the board and card games page.
