Square names used here
GameNow’s Othello names squares the same way in its move preview and move review: columns A to H from left to right and rows 1 to 8 from top to bottom, so A1 is the top-left corner and H8 the bottom-right. The game starts with White on D4 and E5 and Black on E4 and D5. Black moves first, and in solo practice you play Black.
Black’s four legal first moves, D3, C4, F5 and E6, are one move seen through rotation or reflection. Each flips one disc and leaves White three replies; after D3 they are C3, E3 and C5.
Disc count is the wrong scoreboard until the end
The most common beginner habit is choosing the move that flips the most discs. In the middle game that usually works against you. Every move has to be placed next to at least one enemy disc, so each of your discs that borders an empty square offers your opponent a possible square beside it, and a big flip tends to create several such discs at once.
GameNow’s AI is built on the same idea. Its evaluation gives disc count no weight while more than 44 squares are empty (roughly the first 15 moves), a small weight in the middle game, and makes it a major term only when 12 or fewer squares remain. What it weighs instead are corners, mobility, frontier discs and discs anchored to a corner along an edge.
Corners, X-squares and C-squares
A corner disc can never be flipped: no line passes through a corner with a square on both sides of it. Edge discs are the next safest, because a disc on an edge can only be flipped along that edge; every other line through it ends at the border.
The squares that hand corners over are the X-squares, diagonally next to a corner (B2, G2, B7, G7), and the C-squares, beside a corner along an edge (B1, A2, G1, H2, A7, B8, H7, G8). Two small cases, both checked against the game’s rules engine:
- X-square: you hold B2 and C3, your opponent holds D4, and A1 is empty. A1 is now legal for them; it traps B2 and C3 against D4 and takes the corner.
- C-square: you hold A2 and your opponent holds A3. A1 is legal for them and flips A2.
When that danger disappears
The AI’s square table puts numbers on the danger: corners +120, C-squares −20, X-squares −40. Once you own a corner, the X- and C-squares beside it lose that danger for you, because the corner can no longer be given away. In practice games the move preview checks the danger for you: it shows “Opponent can take N corners” whenever your move would leave the opponent a legal corner move, and “Corner secured · cannot be flipped” when your move takes one.
Mobility: count moves, not discs
Mobility is the number of legal moves each side has. The player with more choices can wait for a good one; the player with few ends up forced onto X- and C-squares. When a move neither gives up nor takes a corner, the preview shows “Opponent has N legal replies”, so you can compare candidate moves by how much room they leave. The move review shows both colours’ legal-move counts at every point of a finished game, and how much each move changed them.
Taken to the limit, mobility wins tempo. If your move leaves the opponent no legal move, they must pass and you move again; the game announces it with “Opponent had no move and passed — your turn again”. When neither side can move, the game ends.
Frontier discs and quiet moves
A frontier disc is one that borders at least one empty square. Because every legal move is placed next to an enemy disc, your frontier decides where your opponent can play. When your discs form a compact block inside the cluster and the opponent’s discs surround it, the opponent tends to run short of moves; when your discs line the outside, the reverse happens.
A quiet move flips only interior discs, ones that already have no empty neighbour, so apart from the disc you place it adds no frontier and opens no new squares for the opponent. When two moves flip the same number of discs, prefer the one whose flipped discs are inside. The AI penalises frontier discs throughout the opening and middle game and drops that term only in the last 12 squares.
Edges and wedges
Since edge discs can only be flipped along their edge, edge fights are about gaps. Put White on A3 and A5 with A4 empty, and say White also holds B4 with Black on C4. A4 is then legal for Black (it flips B4), and the black disc on A4 can never be flipped afterwards: the A-file is the only line that could flip it, and both of its neighbours on that file are already White. This is a wedge.
The lesson for your own edges: a single empty square between two of your edge discs is a hole the opponent may later fill with a permanent disc. Before you put a second disc on an edge, check whether it leaves such a gap.
Parity: who gets the last move
The board starts with 60 empty squares and Black moves first, so if nobody ever passes, White plays the 60th and last move. Every pass hands that last move to the other side.
Late in the game the empty squares split into separate regions, and the same counting applies inside each one. The usual heuristic is to move into regions with an odd number of empty squares and leave even ones alone: in an odd region you can expect to take the last square, and the move that fills a region’s last square cannot be answered inside that region.
Endgame: count, don’t guess
In the last dozen squares, mobility and frontier stop mattering and only the final count does. Count the discs at the end of each line you are considering, not after the next move. GameNow’s AI changes method at a set point for each level: when 8 squares are empty on Easy, 10 on Normal, 12 on Hard and 14 on Master, it tries to read the game to the very end, and when that calculation finishes within its time budget the move it picks is exact. Below Master, the level’s random moves still happen at the usual rate.
Two scoring rules matter here. If the game ends with empty squares left because neither side can move, those squares are added to the winner’s total. A resignation or a loss on time is recorded as 64–0.
Practice tools that show these ideas
- Move preview (practice games, on by default): circles the discs a move would flip, draws each flipping line with its count, and lists the flip total plus either the corner risk or the opponent’s reply count. On a touch screen the first tap previews and the second places; with a mouse, hovering previews; on a keyboard the arrow keys move a cursor and Enter or Space places. The Preview button turns it off.
- Undo: takes back your last move together with the AI’s reply. It is disabled in Today’s board, which is ranked.
- Review moves (result screen): steps through the finished game with a slider, showing each move, both sides’ legal-move and corner counts, and the change from the previous move. Buttons jump to the previous or next corner capture, pass or Risk, the position just before you gave up a corner.
- Practice from here: plays on from any reviewed position against the Normal AI, then compares your new line with the original by discs, corners and legal moves, with the reminder that these figures do not prove one line is better.
- Replay from the corner you gave up: shown on the result screen when you conceded a corner. It starts a Normal-AI game from the position just before the move that let the corner go.
Choosing an AI level
The five levels differ in how far ahead the AI reads, how often it plays a random legal move instead of its best one, and when it starts calculating the endgame exactly:
- Beginner: one move ahead, random half the time, no exact endgame.
- Easy: two moves ahead, random 25% of the time, exact from 8 empty squares.
- Normal: four moves ahead, random 8% of the time, exact from 10.
- Hard: six moves ahead, random 2% of the time, exact from 12.
- Master: eight moves ahead, never random, exact from 14.
Depth, Today’s board and the online clock
The depth is a ceiling. A per-move time budget can stop the search earlier on a slow device but never takes it deeper, so the same level does not get stronger on a faster phone. Today’s board picks Easy, Normal or Hard from the day’s seed and ranks your final disc lead. Online games use a clock: five minutes each, five seconds added after every move, and no single move may take longer than 45 seconds; going over either limit loses on time. Practice games have no clock.