I built a chess coach that explains moves like a grandmaster instead of showing engine lines — powered by LLM

Reddit r/artificial Products

Summary

A chess coaching tool that uses an LLM to explain moves in natural language like a grandmaster, replacing raw engine evaluations with contextual coaching narratives. It analyzes user games from Chess.com and Lichess with local Stockfish, detects recurring mistakes, and offers personalized chat and spaced repetition for blunders.

The problem I wanted to solve: Stockfish tells you *what* the best move is, but never *why*. Players under 1800 don't lose because they can't read centipawns — they lose because they don't understand plans, structures, key squares. **What the tool does:** 1. Imports your games from Chess.com or Lichess 2. Stockfish 17.1 WASM runs in your browser (fully local, nothing uploaded) 3. A pattern detector finds 18 types of recurring mistakes across all your games (missed forks, exposed king, bad bishop, neglected development...) 4. An LLM generates coaching narratives in the style of a 2700+ coach **Instead of:** -89 cp · Best: Nc3 Nf6 Be3 **The AI coach says:** > "Bd3 is premature — the bishop attacks nothing and blocks d3 where the queen may want to go. Nc3 was the right move: it defends d4, prevents Black's ...e5 counterplay, and leaves the bishop free to settle on Be3 or Be2 depending on Black's plan." You can also **chat with the coach** — it knows your full game history, opening stats, specific weaknesses. Ask "why do I keep losing with Black in the French?" and it answers with data from YOUR games. Other features: spaced repetition (SM-2) on your own blunders, puzzle rush with real mistakes, 6-month progress tracking. Free tier: unlimited Stockfish. Pro ($14.99/mo, 15-day free trial): LLM coach + chat. https://chessmentorai.com Happy to discuss the prompting approach — getting the LLM to explain chess like a coach (not an engine) was the hardest part.
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