Stockfish
Stockfish is a free, open-source chess engine developed by a worldwide community, widely regarded as one of the strongest engines available and used by many analysis websites and apps.
Stockfish is a chess engine whose source code is open and free for anyone to use. It is built and improved by a large community of volunteers who test changes by playing huge numbers of games. Because it is free and runs on most devices, many analysis boards and chess apps use it behind the scenes to produce their evaluations and best-move suggestions.
It combines a very fast tree search, based on alpha-beta pruning, with an evaluation that includes a neural network component called NNUE. It can also use endgame tablebases to play some endgames perfectly. Its strength is far beyond any human, so its output should be read as a reliable guide to what is objectively best, not as a model of what a person would play.
For study, Stockfish is excellent at confirming tactics, spotting blunders and showing the best defense in a lost position. Its weakness as a teacher is that it does not explain its ideas. When it recommends a surprising move, spend time working out the plan behind it. Run it after you have analyzed a game yourself, not before.
A neighboring idea is Neural network engine. A neural network engine uses a trained neural network to evaluate positions, and NNUE, the efficiently updatable neural network added to Stockfish, combines such an evaluation with fast traditional search.
Also worth reading is Syzygy tablebases. Syzygy tablebases are a compact set of endgame tablebases created by Ronald de Man that cover endgames up to seven pieces and are widely used by modern chess engines.
Compare it with Minimax. Minimax is a decision method in which one side tries to maximize the evaluation while the opponent tries to minimize it, forming the basis of how traditional chess engines choose moves.
Computer terms such as "Stockfish" are most useful next to a coach who reads your games with you, which is how a first lesson with George Li works.
Related terms
A chess engine is a computer program that searches positions and evaluates moves, usually playing and analyzing far stronger than any human, and it is used for analysis, preparation and play against a machine.
An evaluation is a numerical judgment of who stands better in a position, usually given in pawns from White’s point of view, where positive favors White and negative favors Black.
A neural network engine uses a trained neural network to evaluate positions, and NNUE, the efficiently updatable neural network added to Stockfish, combines such an evaluation with fast traditional search.
Alpha-beta pruning is a search technique that skips branches of the move tree that cannot change the minimax result, letting engines look much deeper using the same amount of computing time.
An endgame tablebase is a precomputed database that gives the exact result and best moves for every position with a small number of pieces, so engines can play those endgames perfectly.
Engine analysis is the use of a chess program to search a position and report which moves are strongest, along with a numeric evaluation and the lines it expects both sides to follow.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
How much does chess coaching cost?
Published rates for private, group and subscription chess coaching, with the source and the date of each.
A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.