Side project · 2026 · Built end-to-end
A chess coach that explains every move in plain English — and the first thing I built to find out what AWS could actually do for me.
I got back into chess. I played a lot, I lost a lot, and I could not say why — the games just ended. The obvious answer was a Chess.com subscription. I did not want to pay for one, and I wanted the practice more than I wanted the tool.
So I built the thing I wanted: something that watches the games I actually play against friends, names the mistake I keep repeating, and tells me the move where my opening knowledge runs out. The chess was the excuse. The real goal was to stop reading about AWS and put something live on it — a pipeline that runs on a schedule, costs nothing, and keeps working when I close the laptop.
Play Stockfish at eight strengths. After each move the coach gives a verdict, the reason in one sentence, the move that was better, and the engine lines you can step through on the board. Every sentence is built from facts the position actually shows — a hanging piece, a fork, material won along the line — so it never claims something the board does not back up.
It downloads my Chess.com archive, analyses every game with Stockfish, and groups the mistakes by what went wrong rather than by game. One habit at the top accounts for a quarter of my errors — which makes it the only thing worth practising this week. Each pattern carries real examples you can open on the board.
Twenty openings and forty-nine lines, each move with a reason. Learn mode walks the line; Practice mode makes you find the moves and judges the wrong ones with the engine. The report ties back into it: it knows the move where I leave the book in each opening, and sends me to that exact line.
No server and no database. A schedule wakes a function, the functions write files, and the browser reads them.
Every stage writes a file and stops. A failed analysis retries on its own from the queue without replaying the download, and the browser only ever reads finished files — so a slow Stockfish run never makes the page slow.
The engine runs as WebAssembly inside the function, one game per invocation, about a minute each. Roughly ninety games a month is a rounding error against the free tier.
The whole stack is a CDK app: one command builds it, deploys it, uploads the site and clears the CDN cache. Tearing it down and rebuilding it is how I learned what each piece was actually for.