Not another engine clone
The Baronet plays with its own engine, written from scratch, and its own neural network. At full strength it is rated over 2700 in blitz on Lichess (September 2026).
An original engine
Many free chess programs are a new window around Stockfish or another open-source engine. The Baronet is not. Its search and its evaluation are written from scratch in Embarcadero Delphi (Object Pascal), and it uses no source code and no neural-network weights from another chess engine. The program you download is the same engine that plays on Lichess.
This page explains how it works, for readers who are curious. You do not need any of it to play.
How it chooses a move
Like every strong engine, The Baronet looks ahead. It considers its possible moves, the replies to each, the answers to those replies, and so on, then chooses the move that leads to the best position it can guarantee against the best defence. This is the alpha-beta search, and its whole art lies in not looking at everything: out of the millions of possible sequences, most are obviously bad and can be cut off early.
The search deepens one move at a time (iterative deepening), tries the most promising moves first, and remembers positions it has already met in a transposition table, since the same position is often reached by different move orders. Moves that are unlikely to matter are searched less deeply (late-move reductions), hopeless branches are dropped early (null-move pruning, futility pruning, razoring and ProbCut), and a move that stands out as the only good one is searched more deeply (singular extensions). At the end of each line, a quiescence search plays out the captures so that the engine never stops its calculation in the middle of an exchange.
The engine can also search with several threads at once (lazy SMP) and keep thinking on its opponent's time (pondering); that is how it plays its rated games on Lichess.
How it judges a position
At the end of every line, the engine has to say how good the position is. The Baronet uses an NNUE - an “efficiently updatable neural network”, the approach that transformed computer chess in 2020. The network looks at where every piece stands relative to each king and returns a score; it is designed so that after a move only a small part of it needs to be recomputed, which keeps it fast on an ordinary processor.
The Baronet's network was trained from scratch for The Baronet, with the open-source bullet trainer. The training positions come from the engine's own games against itself, supplemented by positions from the public-domain (CC0) Lichess database. Their scores come from a deep search by a locally-run reference engine. No pre-trained network and no training set under a restrictive licence were used.
What it knows by heart
- An opening book, so the first moves of a game follow established theory and vary from game to game. It can be switched off.
- Syzygy endgame tablebases for every position with up to four pieces, probed through the open-source Fathom library. In those endings The Baronet knows the exact result of every position: it does not let a win slip, and it does not lose a drawn ending.
Tested by games, not by guesses
Chess engines are full of ideas that sound right and lose games. So every change to The Baronet is decided the same way: the new version plays thousands of fast games against the previous one, and a statistical test (SPRT) decides whether it is really stronger. Puzzle suites and benchmark scores are used only to catch breakage; they have been wrong too often to be trusted with a decision.
The same discipline removes as well as adds. In September 2026, a weekend of such tests removed a series of older search rules that no longer earned their keep with the neural network; the simpler engine won by more than 100 Elo against the version before it.
Strength
At full strength, The Baronet is rated over 2700 in blitz on Lichess (September 2026), where it plays rated games against humans and other engines. The strength settings in the program hold it back for everyone else: see Features.
For engine developers and testers
The desktop program can play matches against other engines through cutechess-cli, directly on its own board. The Baronet itself is closed-source: the program is free, but its code and its network are not published.
Play against it
The full-strength engine is in the free download. So are the easier levels.
The Baronet Mark IV - 0.300 · Windows 10/11, 64-bit · macOS 11+, Apple Silicon & Intel · Updated September 2026