Flip Discs — Reversi Strategy Game vs Computer
Place discs to flip your opponent's pieces. Most discs of your colour when the board is full wins.
How to play
- Click any bright-green highlighted cell to place your black disc.
- Your disc must outflank at least one white disc in a straight line.
- All outflanked white discs immediately flip to black.
- The AI plays white — it picks the move that maximises disc count + corners.
- When the board is full or neither player can move, the player with more discs wins.
Place black discs to outflank and flip the AI's white discs. Valid moves are highlighted in bright green. The player with the most discs when the board is full wins.
How it works
Flip Discs is an implementation of Reversi (also sold as Othello). Two players take turns placing discs of their colour on an 8x8 board. Each newly placed disc must outflank at least one of the opponent's discs — that is, the new disc and an existing friendly disc must bracket one or more opponent discs in a straight line (horizontal, vertical, or diagonal). All outflanked discs flip to your colour.
The game begins with four discs in the centre — two of each colour in a diagonal arrangement. Play proceeds until neither player can make a legal move (usually when the board is full). The player with the most discs of their colour at that point wins.
Counter-intuitively, having more discs mid-game is not always good. A large disc count means the opponent has many flanking opportunities and can flip large swaths of the board with a single move. Experienced players often prefer fewer but strategically placed discs, prioritising corner cells (which can never be flipped) and stable edges.
The AI in this widget uses a positional evaluation strategy, so it will contest corners and edges actively. This makes the game a genuine challenge and rewards players who think two to three moves ahead.
Worked example
Capture a corner to build a stable region
- In the early-to-mid game, look for a move that places your disc in any of the four corner cells.
- Click the corner cell — verify that it outflanks at least one AI disc along a row, column, or diagonal.
- The corner disc is now permanently yours; it can never be flipped because it cannot be outflanked from any direction.
- On subsequent turns, build along the edges adjacent to the corner, creating a stable wall of discs the AI cannot recapture.
- Continue expanding your stable region while limiting the AI's access to the opposite corners.
A stable corner and edge position that resists being flipped, giving you a strong endgame advantage.
Common mistakes to avoid
- Playing for maximum disc count every turn — large mid-game disc totals are easily reversed and can leave you with fewer moves.
- Placing a disc adjacent to a corner (the X-square) without owning that corner, which often gives the AI a free corner capture on the next move.
- Ignoring the opponent's mobility: a move that gives the AI many new legal moves on their next turn is usually worse than a move that limits their options, even if your immediate disc gain is smaller.
Key terms
- Outflank
- To place a disc such that one or more opponent discs are bracketed between your new disc and an existing friendly disc in a straight line; those opponent discs then flip.
- Stable disc
- A disc that can never be flipped for the remainder of the game, typically corner and edge discs that are fully surrounded in all directions.
- Parity
- The concept that having the last move in a region is advantageous; controlling parity (usually by keeping an odd number of empty cells in key regions) is an advanced technique.
Frequently asked questions
- How does flipping work?
- When you place a disc, every straight line (in any of 8 directions) that starts with your disc, contains one or more opponent discs, and ends with another of your discs — all opponent discs in those lines are flipped to your colour.
- What if I have no valid moves?
- Your turn is skipped and the AI plays again. If neither player has a valid move, the game ends.