The best first move in Reversi

Most pages that answer this question guess. This one asks the engine, at the moment the page is built, and prints whatever comes back.

Black's four legal first moves

A move is legal in Reversi only when it traps at least one enemy disc in a straight line between the new disc and one you already own. From the standard opening position, White on d4 and e5 and Black on d5 and e4, only four squares manage that for Black.

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Every other empty square flips nothing, so it is not a move. How legality works covers the rule in full, and board setup covers where the first four discs go.

What the engine says about each one

The table below is generated when this page is built. For each of the four openings, the engine is handed the position after Black's move and asked for White's best reply. The evaluation is written from White's point of view, so a negative number means White thinks Black is slightly better off.

All four come back with exactly the same number, -775. Every search reached the same depth, 6. The replies are not the same square, but they are the same square seen from a different angle, which is the whole point.

Why they are the same position

The starting position has a particular kind of symmetry. White sits on d4 and e5, which is one diagonal, and Black sits on d5 and e4, which is the other. Three ways of moving the board leave that arrangement exactly as it was, colours and all: a half turn, a flip across the a1 to h8 diagonal, and a flip across the a8 to h1 diagonal. Add doing nothing at all and there are four.

A quarter turn is not one of them. It leaves the shape of the four centre discs alone, but it lands White's discs on the squares Black was using, so it gives you the same position with the colours swapped rather than the same position.

Those three moves are enough to connect all four openings. A half turn takes d3 to e6 and c4 to f5. A flip across the a1 to h8 diagonal takes d3 to c4 and e6 to f5. Put them together and every one of Black's four first moves is reachable from every other, which is exactly what "they are the same move" means.

Every row checks out. The four turns cover all four of Black's openings, each turned board matches the real position exactly, and the engine's reply in each case is the base reply put through the same turn.

The four positions, side by side

Here is each opening on a real board. Look at the shape of the three discs rather than where they sit, and the four pictures are one picture.

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In each case White has 3 replies, and in each case they are the same three squares turned the same way. The game does not start to differ until White chooses. Written in the standard f5 notation, those three replies are f6, d6 and f4, and they are the roots of the three families every named opening belongs to: diagonal, perpendicular and parallel. The openings index.

So which one should you play?

1. Play f5 if you want to read opening books. Almost every published Othello opening line starts f5, because the notation was standardised that way. Nothing about the position is different.
2. Play whichever you like otherwise. Against a human it makes no difference at all.
3. Do not spend time on move one. The first move that actually matters is usually move five or six, once the two players have chosen which family of openings they are in. Opening strategy.

How this page was made

The site runs the same Reversi engine that plays you on the board pages, and it runs during the build. For each opening, the engine searches the position after Black's move and returns its chosen reply, its evaluation and how deep it looked. The symmetry checks compare the actual 64-square boards rather than a description of them.

If the engine ever disagreed with the symmetry argument, this page would print that instead. How the engine works.

Try it against the computer

Play the computer and open with each of the four in turn. The games will feel identical, because they are, and that is a useful thing to have seen for yourself.

Next: opening strategy, the named openings, tips for beginners, or the full strategy guide.