Chess post-mortem skills for Claude Code

Claude Code skills that turn one of your chess games into a post-mortem you can actually read: plain-language explanations of your mistakes, checked against Stockfish, and a narrated video of the whole game.

The video

https://github.com/user-attachments/assets/ebd443e1-aeac-41d3-a868-64d521223a9b

6:49, English narration, subtitles.

This is a real game of mine: a 15+10 rapid on lichess (5KmlrdyT), White, Open Sicilian against a Najdorf, around 1700. During the game I recorded myself thinking aloud, in French, with a plain voice recorder running next to the board. After the game I gave Claude two things: the lichess link and the mp3.

Claude transcribed the audio locally with whisper.cpp, then used the clock times in the PGN to match each sentence to the move I was deciding at that moment. So when the video says "at move eight you asked yourself whether the bishop belongs on c4 or e2", that is my own question, answered with the engine. Everything the video shows (the transcript, the Stockfish sweep, the annotated PGN, the storyboard) is in examples/game-010/.

Why this exists

A Stockfish analysis gives you numbers and lines. It is not fun to read, and often it does not tell you why: -1.8 after your move, and a 12-move variation you would never find at the board.

I realized Claude can drive Stockfish itself. It asks the engine the questions a human would ask ("why not the move I played?", "what if Black simply takes?"), keeps asking until the answer makes sense, and writes it down in human terms. And since it knows what I was thinking during the game, it can refute my actual reasoning instead of a guessed one. After the analysis I can keep asking my own questions about any position, and it checks them with the engine before answering.

Is it for you?

Probably yes if:

• you play slow or rapid games and want to learn from them, not just see where the eval bar dropped;
• you are fine running Claude Code on your machine;
• you are willing to take notes or talk during the game (optional, but this is what makes the result interesting).

Probably not if you want a quick check of a blitz game. Lichess or chess.com analysis does that in seconds.

It takes time. A full run (sweep, investigations, annotations, video) takes around one hour of processing. Use it on games where you took the time to think, not on every game you play.

Give it your thoughts. I strongly recommend passing your written notes or an audio recording covering the whole game. Without them you get a good engine explanation. With them you get a review of your reasoning: which fears were justified, which plans were sound, which questions you asked yourself and what the answer was.

Hallucinations. The AI can still get something wrong. Every claim is checked against Stockfish and a verifier pass re-reads the result, so in my experience errors are rare. If something looks off, ask Claude to check that position with the engine.

My workflow

1. Play a game with some time to think (15+10 rapid, or correspondence).
2. Record myself thinking aloud during the game (any phone or web voice recorder). For correspondence games, I write notes per move instead.
3. After the game, open Claude Code and say something like: "analyze this game: , here is my think-aloud recording: ".
4. Wait about an hour. I get an annotated PGN and a standalone HTML analysis board.
5. Ask for the video: "make a video of this game".
6. Read, watch, then ask questions about the positions I still do not understand.

The skills

The skills are written for Claude to read, so the SKILL.md files double as the documentation. Start with skills/chess-analysis/SKILL.md.

Install

Copy (or symlink) the skill folders into .claude/skills/ of your project, or into ~/.claude/skills/ for all projects:

git clone https://github.com/brumar/chess-postmortem-skills
cp -r chess-postmortem-skills/skills/* ~/.claude/skills/

Then ask Claude something like "analyze this game: " or "make a video of game 010".

Requirements

You do not need to set these up by hand. Claude Code can most likely install them for you: ask it to "install the dependencies for the chess skills" and it will read the list below and the SKILL.md files.

• Python venv with python-chess, cairosvg (analysis), plus pillow, piper-tts for the video. The skills assume a .venv-chess at the repo root and create it if missing.
• Stockfish. scripts/get_stockfish.sh uses $STOCKFISH or the one on PATH, else downloads the official Linux binary.
• For video: ffmpeg, and a piper voice (download command in chess-video/SKILL.md).
• Optional: whisper.cpp for think-aloud transcription.

Game files live in a chess-games/ folder at the root of the project you run Claude in (games/, boards/, video/).

Tell Claude your level

Every comment is pitched at a reader level (audience.level in annotations.json). For your own games, tell Claude your level once and make it stick, for example in your CLAUDE.md:

My lichess handle is <handle>. Write chess analysis for a 1800 player.

Without it, the skill uses the PGN's Elo for the reviewed side and asks when that is missing or provisional.

Example files: game 010

To regenerate the video, download the piper voice into examples/game-010/video/voices/ and run make_video.py on the storyboard.

License

MIT, except the vendored chess.js (BSD 2-Clause) and the cburnett piece set (CC BY-SA / GFDL). See LICENSE.