Jevchess — choxos

Yes. The site lends its own keys within a daily budget of Jev tokens, LLM requests, and OpenRouter credit, with a per-visitor share and a cap on dear models. Your own TypeSafe or OpenRouter key lifts the cap.

Code owns the game and Jev supplies judgment. Code lists every legal move with chess.js, writes out captures, checks, safety, threats, and material, then sends one request per move with a move Choice and an evaluation Score.

LLM opponents get the same position and described move list. Schema-capable models must return JSON with a legal move and the rest reply with a short idea plus a MOVE line; after three misses a random legal move is played and counted.

Keys stay in browser local storage or server .env and a TypeSafe key passes through a small relay that never stores or logs it. Saved games are rebuilt field by field before saving; self-hosting needs Node.js 20.3 or newer with no dependencies.

One request per move, roughly 3,000 input tokens, about 300 ms. At $0.042 per million input tokens a whole game costs Jev well under a cent, and the recorded wording comparison puts a game at about $0.004. When you play Jev yourself it answers in about a third of a second, and Stockfish, which needs no key at all, thinks for 0.3 s a move.

Because it was tested. A shorter wording of the same facts costs 14% fewer tokens, but over six games each against Stockfish 1320, judged move by move by a full-strength Stockfish, Jev lost 115 centipawns a move with the full wording against 125 with the short one and blundered on 26 moves against 34. The README calls that gap within the noise, but it points one way and a game is cheap, so the full wording stays. test/ab.mjs reruns the comparison after any change to what the models read.

Jev versus machines picks Stockfish 19 at Elo 1320 up to full strength and any number of OpenRouter LLMs, with Jev as White, Black or both, all games running at once on a split screen and a closing table of wins, draws, losses, time per move, illegal-move misses and cost. You versus Jev takes drag, click, typed or spoken moves. Saved games replay move by move, export PGN or share a link. Stockfish is the lite single-threaded WebAssembly build of Stockfish 19 running in your browser, strength set through UCI_Elo.