About Prep DB

What this is

Prep DB is a speed-first chess database: 3,245,216 tournament games behind a transposition-aware opening explorer, opponent preparation tools, and an engine that runs entirely in your browser. Opening statistics are computed from the 1,964,188 over-the-board games; online games are searchable and used for preparation, but never distort opening theory percentages.

Data sources

Games are compiled from The Week in Chess by Mark Crowther, the longest-running chess news and games service — new issues are ingested automatically every week. If you find TWIC valuable, consider supporting it. Every game is validated by full replay, de-duplicated, and quality-filtered (rating floor 1800, no engine games, standard chess only). Opening names come from the Lichess chess-openings dataset.

Your analysis is private

The engine is Stockfish 18 compiled to WebAssembly, running multithreaded on your own device. Positions you analyse, games you import, and evaluations are never sent to a server. We use privacy-friendly, cookie-less page analytics to understand aggregate usage.

Built on

Stockfish (GPL), chessground and chessops from the Lichess ecosystem, Postgres, and Rust. Position statistics are keyed by Polyglot Zobrist hashes, so transpositions are first-class.

Corrections

Spotted a mis-attributed game or a player listed under two spellings? Player records are curated by hand — reach out and it will be fixed: hello@prepdb.io.

Explore the openings library or jump straight into the explorer.