Main line

In an annotated game, the main line is the path read continuously. Variations branch from it to show alternatives and then return to the relevant point. In Portable Game Notation (PGN), the main line remains outside parentheses while side branches appear inside them.

When a real game is annotated, the main line is usually the sequence played on the board. In material about openings, the first phase of a game, it is often an established and heavily studied continuation. In chess engine analysis, where a program calculates positions, it may be the line the engine currently regards as best.

Main can therefore identify the central path of a presentation, the line actually played, or a particularly important continuation. It does not guarantee that this is the only correct option or that every analysis will rank it best. In a variation tree, a branch can be promoted to the main line without changing its moves; only the path treated as central changes.