Stockfish 18 explained: depth, evaluation and engine lines

A plain-language guide to reading a chess engine: what +1.50 means, what depth and nodes are, and how to use multiple engine lines.

Stockfish is a free, open-source chess engine and has been one of the strongest in the world for years. ChessAnalyzer runs Stockfish 18 directly on your phone or in your browser. This guide explains the numbers it shows.

The evaluation

The big number is the evaluation, in pawns, from White's point of view. +1.00 means White is better by roughly a pawn; −2.50 means Black is better by two and a half pawns; 0.00 means level. A score like #5 means a forced checkmate in five moves (negative for Black). As a rough guide, up to about ±0.50 is balanced, around ±1.50 is a clear advantage, and beyond ±3.00 is usually winning with good play.

Depth, nodes and speed

• Depth is how many moves ahead the engine has searched along its main lines. Higher depth means a more reliable evaluation. Modern engines prune hopeless lines, so their "depth" goes deeper on the important variations.
• Nodes is the number of positions examined, often millions.
• NPS (nodes per second) tells you how fast your device is calculating.

Engine lines (MultiPV)

By default ChessAnalyzer shows the engine's three best moves, each with its own evaluation and the continuation it expects. Comparing the lines is often more instructive than the best move alone: if the top three moves are all close, the position is flexible; if the best move is far ahead of the second, there is one precise idea you need to find.

Why the evaluation can change

An evaluation at low depth is a first impression. As the engine searches deeper it can find a hidden resource and change its mind. That is why ChessAnalyzer's Smart Deep Review spends extra time on the critical moments: the positions where a deeper look matters most.

NNUE: how Stockfish evaluates

Stockfish evaluates positions with an efficiently updatable neural network (NNUE) trained on huge numbers of positions, combined with a classic alpha-beta search. The phone and full web versions use the full networks; the lightweight web version uses a smaller network that loads in seconds.

Stockfish is free software under the GNU GPL v3. ChessAnalyzer is independent and not affiliated with the Stockfish project.