Play Zugwunder
Zugwunder is copyright © 2026 by Erik Schmidt, all rights reserved. Zugwunder, Wolfgang and the UCI engine for Linux can be downloaded free of charge here.
What the evaluation means
After each of its moves, Zugwunder shows how it judges the position, for example Evaluation −1.25 (White's view) · depth 14.
- Evaluation
- Who is better, measured in pawns and always seen from White's side. Positive numbers favour White, negative numbers favour Black. +1.00 is roughly an extra pawn for White, −3.00 roughly an extra knight or bishop for Black.
- Around 0
- Between −0.30 and +0.30 the position is about equal; small values also reflect the advantage of having the move.
- Large values
- From about ±2 the game is usually decided with correct play; values like −15.70 mean one side is overwhelmingly ahead, usually by a queen or more, or a mating attack is coming.
- Zugwunder sees mate in n
- Zugwunder has found a forced checkmate in n of its own moves, whatever you play.
- You could mate in n
- You have a forced checkmate in n moves, if you find it.
- Depth
- How many half-moves (one move by one side) Zugwunder looked ahead on its main line, with the most important replies followed further. Higher is more reliable; the lower strength levels search shallowly on purpose, so their evaluations are rougher.
The evaluation is Zugwunder's own opinion, not the truth: it can be wrong, especially at low depth.
Game results: checkmate ends the game, and draws are announced for stalemate (no legal move, but not in check), the fifty-move rule (50 moves by each side without a capture or pawn move), threefold repetition of the same position, and positions where neither side can mate (for example king against king and bishop).
About Zugwunder
Zugwunder is a powerful chess engine developed from scratch in Swift by Erik Schmidt. It runs on macOS and Linux and can be integrated into other chess programs via the UCI protocol. On this page, you can play against Zugwunder directly in your browser, with no installation required.
The engine is an alpha-beta searcher with an estimated playing strength of around 3000 Elo. Positions are evaluated by a small neural network (NNUE) that learned chess solely from Zugwunder itself: the engine played hundreds of thousands of fast games against itself, the positions were labelled with its own search results and the game outcomes, and each new network had to beat the old one before it was adopted. The current network is the fifth generation. No change to the engine is kept unless it first wins thousands of test games against the previous version.
This page runs the same engine as WebAssembly in your browser, using one thread and running at about a third of the native speed. It therefore plays somewhat weaker here, but at full strength it is still far stronger than almost any human player.
More information and downloads: https://f97.be/zugwunder.html