Calvin is a chess engine written by @kelseyde.
It is written in Java (JDK 21).
Currently playing on Lichess: https://lichess.org/@/Calvin_Bot
Ranked ~300th on the Computer Chess Rating Lists blitz leaderboard: https://www.computerchess.org.uk/ccrl/404/
The table below tracks the strength of release versions, on the CCRL computer chess leaderboards and on Lichess.
| Version | Release date | Lichess | CCRL Blitz |
|---|---|---|---|
| 3.3.0 | 2024-05-10 | ~2550 | 2453 |
| 3.2.0 | 2023-12-09 | ~2400 | 2233 |
| 3.1.0 | 2023-12-05 | ~2390 | - |
| 3.0.0 | 2023-12-02 | ~2380 | - |
| 2.6.2 | 2023-11-12 | ~2300 | 2173 |
- Bitboards of each piece type/colour are used for internal board representation.
- Legal move generation - pseudo-legal moves are not generated.
- Magic bitboards are used for sliding piece move generation.
- Iterative deepening search + negamax.
- Quiescence search to combat the horizon effect.
- Principal Variation Search
- Lazy SMP multi-threaded parallel search.
- Transposition table with Zobrist hashing.
- Null-Move Pruning
- Futility Pruning
- Reverse Futility Pruning
- Late Move Reductions
- Delta Pruning
- Texel Tuning: all evaluation parameters are tuned using Texel's tuning method.
- Material: basic material count, bishop pair bonus
- Piece square tables: asymettrical PSTs
- Tapered eval: evaluation tapered based on opening/middlegame/endgame phase
- Pawn structure: passed pawn bonuses, isolated/doubled pawn penalties.
- King safety: bonus for a pawn shield around the king, penalty for a pawn storm towards the king, penalty for open file around the king.
- Incremental updates: Evaluation is updated incrementally with make/unmake move
- Simple opening book loaded from a .txt file on startup. Can be disabled using the 'OwnBook' UCI option.
- Calvin can probe the Lichess Tablebase API for endgames of 7 men or fewer. Can be disabled using the 'OwnTablebase' UCI option.
- Calvin communicates using the Universal Chess Interface (UCI) protocol.
- Pondering, where the engine thinks on the opponent's move. Can be disabled via the UCI.
- Hash size and number of Lazy SMP threads are also configurable via the UCI.
- Calvin is connected to Lichess where he plays regularly in the engine pool: https://lichess.org/@/Calvin_Bot
| Depth | Nodes | Speed |
|---|---|---|
| 1 | 20 | PT0.000004S |
| 2 | 400 | PT0.000009S |
| 3 | 8902 | PT0.003844S |
| 4 | 197281 | PT0.025309S |
| 5 | 4865609 | PT0.123557S |
| 6 | 119060324 | PT1.363415S |
If you would like to contribute, or just talk about chess/chess programming, get in touch!
