Game phases and critical moves

Opening, middlegame, endgame

Ironwood uses the following rules to classify each move:

One half-move is a move by one player. The opening rule takes priority even if little material remains during those first 20 half-moves.

To calculate the material total, count the pieces remaining for both players together:

For example, if each player has one rook, one bishop, and one knight, the total is 22 points: (5 + 3 + 3) × 2. After the opening, that is classified as endgame. Adding one queen makes the total 31 points, which is middlegame.

The classification uses the board before each move. A capture that reduces the total to 26 or below therefore changes the phase for the following move. Material is checked again for each move; a promotion can raise the total back above the threshold.

These are approximate study categories, shared by the expanded graph, phase summaries, and printed reports. They may differ from how a player describes the position.

In Analysis → Summary, the accuracy and average CPL comparison charts show Overall, Opening, Middlegame, and Endgame groups. Each group places White’s gold bar beside Black’s sage green bar, with values and per-player phase move counts. Higher accuracy and lower average CPL are better. A faint gold background marks the current phase; click a player’s phase bar to jump to that player’s first move in it. A phase the game never entered is marked Not reached. See Accuracy and CPL for reading the charts, missing values, and the two different scales.

Phases on the expanded graph

In the Analysis tab, click Expand inside the graph’s upper-right corner, or right-click the graph and choose Expand analysis graph. Colored background bands mark the phases across the move timeline: blue for opening, purple for middlegame, and green for endgame. A colored strip and boundary lines show where each phase starts and ends; phase names appear above bands when there is room. The legend remains visible even for a short phase.

Hover a position to see its phase in the tooltip, or click it to see Game phase in the details below. Phase shading also covers unanalyzed positions; gaps in the evaluation line still mean those positions have not been analyzed. The graph uses the same phase classification as the summaries and report. These are approximate study categories, so their boundaries may differ from how you would describe the game yourself.

Critical moves

An inaccuracy, mistake, or blunder may be a critical move because it changes the player’s chances. Mate-related swings can also be critical. Ironwood can revisit positions immediately before and after these moves with a larger search budget. This is verification: a second look intended to make the judgments more reliable.

A turning point is a position highlighted because the evaluation or move quality changed sharply. It is a place to start asking what changed on the board. It does not automatically mean that one move alone decided the game.