Credits & licences

What this course is built on, and on what terms.

The engine

Every evaluation, every measured threshold and every judgement drill in this course is computed by Stockfish 18 — specifically Stockfish.js 18.0.8, the official WebAssembly build, running entirely in your own browser. No position you analyse here is sent anywhere.

Stockfish is © T. Romstad, M. Costalba, J. Kiiski, G. Linscott and the Stockfish contributors, with neural-network evaluation by Linmiao Xu. The JavaScript/WebAssembly port is maintained by Nathan Rugg. It is free software under the GNU General Public License, version 3, and it is included here unmodified. Its complete source:

• github.com/official-stockfish/Stockfish — the engine
• github.com/nmrugg/stockfish.js @ 93c9945 — the exact source tree the shipped WebAssembly build was published from
• stockfish-18.0.8.tgz — the published artefact itself (sha512 z+f2UMPX…MQVWtQ==; the full digest is in stockfish-SOURCE.txt)

Corresponding Source. The WebAssembly engine served from this site is conveyed under GPLv3 §6, and its Corresponding Source is served from this site too, for as long as the site is up and at no charge:

• stockfish.js-93c9945-source.tar.gz — the complete source tree the shipped build was compiled from, engine included (578 KB; sha256 ef9b6e9bd66de9869dc4715979ada23c6ab4fa96648025823a0a865f300667b2)
• nn-9067e33176e8.nnue — the neural network the build evaluates with, named in src/lite_nets.h of that tree (6.4 MB; a Stockfish network is named for its own sha256, so the file verifies itself)

Those two are everything needed to rebuild what this site serves; the upstream links above are given as well, and are where the files came from. Should this site ever stop serving them, Foresight Engineering will supply a copy on a durable medium or by download, for no more than the cost of conveying it, to anyone who asks at zwoods@4sightengineering.com, for at least three years from the date this build was first served. This offer applies to Stockfish and Stockfish.js only; nothing else on this site is GPL software.

This course is not affiliated with or endorsed by the Stockfish project.

The data

The claims this course makes are only as good as what they were measured against, so the sources are listed the same way the thresholds are.

• Tactics puzzles come from the Lichess puzzle database, released by Lichess under the CC0 public-domain dedication and rated by the millions of players who solved them. The ratings your drills are graded against are theirs.
• Endgame drills are graded against the Syzygy tablebases by Ronald de Man — the solved, mathematically final truth of chess with few pieces — generated using the Lichess tablebase server. When this course says an ending is “won”, that is who says so.
• Master games used to build the recognition drills come from the Lichess masters database, via its public opening explorer.
• Pawn structures — the positions behind the structure nodes — were read out of one month of ordinary rated games, the January 2013 standard dump from the Lichess game database, released by Lichess under the CC0 public-domain dedication. Club games, not master games, on purpose: a structure you will actually meet is one that turns up in the games people really play.
• Club games — the corpus behind the outcome calibration (what an advantage is actually worth at 1500) and the judgement studies — were sampled from public games via the Chess.com published-data API. What ships is aggregate tables and sampled positions; nobody’s games are redistributed.

Lichess deserves a sentence of its own: a free, open-source, advertising-free chess server that also publishes its data for anyone to build on. This course leans on that generosity three times over. lichess.org

The book’s diagrams

The diagrams in The Ascent — eight hundred and nineteen plates across its five parts, and the PDF editions — draw their pieces with the cburnett chess piece set by Colin M. L. Burnett, which its author released under a choice of licences including the BSD licence and Creative Commons Attribution-ShareAlike 3.0. The set and its exact terms are on Wikimedia Commons. The plates were recoloured into this site’s ink and red; the pieces themselves are his. The board uses the same set: the twelve drawings in /pieces/cburnett, recoloured the same way, so a position in the book and the same position on the board are one object. The board used to draw Unicode characters in whatever symbol font your machine had, which made it a different set on every device.

Type & voices

• Set in Oswald (The Oswald Project Authors) and Spectral (Production Type), with Caveat (Impallari Type) and Italianno (TypeSETit) on the letter. All four are under the SIL Open Font License 1.1 and are served from this site — no page contacts Google — with each licence beside the files: Oswald, Spectral, Caveat, Italianno.
• The instructors’ voices were generated with ElevenLabs. The instructors themselves are fictional.
• The music — the bed under the start screen, the sting, and the ambience in the match room — was generated with Suno to prompts written for this course.
• The instructors’ portraits and the monolith mark were generated with ChatGPT to prompts written for this course, and then cropped and recoloured here. They are not photographs of anyone, and nothing on this site is archival.
• Move generation and legality on every board use chess.js by Jeff Hlywa, under the BSD 2-Clause licence, served from /vendor/chess.js.

Everything else

The curriculum, the textbook and its diagrams, the drills, the board, and the measurement studies are original to this course. Every threshold the app uses cites the study that set it, and the studies are written so they can be re-run and disagreed with — that is the point of them.