Free Online Chess Engine

The number next to each candidate move — like +2.18 — is the evaluation in pawns, from the perspective of the side to move. Positive means an advantage for whoever moves next; negative means the position favors the other side. A swing from roughly 0.00 to +1.00 is a small but real edge, similar to being up a pawn with no compensation; +3.00 or more is usually a decisive material or positional advantage.

Under the hood, the engine actually computes in centipawns — hundredths of a pawn — which is why you'll see evaluations like +218 in raw engine output. This site converts that to the more readable +2.18 automatically.

When the engine finds a forced checkmate, it stops reporting a centipawn score and shows a mate score instead — M4 means mate in 4 moves for the side to move, -M3 means getting mated in 3 if the opponent plays perfectly. These only appear once a forced sequence is within the engine's search horizon, so a real mate can exist on the board without yet showing as M-something at a shallow depth.

Depth is how many moves ahead the engine has fully analyzed along its main lines — not a fixed number of positions, since modern engines prune branches that clearly don't matter and search promising ones much deeper. A higher depth generally means a more reliable evaluation, but even a relatively shallow depth from Stockfish is far stronger than casual human calculation in tactical positions.

This engine runs a time- and depth-bounded search tuned for a fast, accurate answer rather than the deepest possible search, so you get a strong evaluation in a second or two instead of waiting minutes for marginal extra precision.

The principal variation (PV) is the full sequence of best-play moves the engine expects from the current position — not just the next move, but the likely continuation for both sides. MultiPV controls how many separate top lines the engine reports at once; this analysis board runs MultiPV 3, so you see the best move alongside the second- and third-best alternatives, each with its own evaluation and principal variation.

Comparing the top few lines side by side is often more useful than the single best move alone — it shows you how much better one option is than the next, and whether a position has one clearly correct idea or several roughly equal choices.

Stockfish is a free, open-source chess engine and, by rating, the strongest chess-playing entity in the world — well beyond any human grandmaster. It combines an efficient alpha-beta search with NNUE (Efficiently Updatable Neural Network) position evaluation, the same core technology used in official engine tournaments.

This site runs Stockfish entirely as WebAssembly inside your browser tab. Positions are never sent to a server for analysis — the same privacy guarantee as the rest of this site's tools.