Claude Code Found My Pirc and King's Indian Mistakes
By Steven Van ·
Quickchat's co-founder ran a four-hour unattended Claude Code session with Stockfish 19 and got an eleven-page brochure of nine positions.
Quickchat's co-founder Piotr Grudzień has published a write-up of an unattended Quickchat blog experiment: he pointed Claude Code and Stockfish 19 at 2,000 of his chess.com blitz games to find the Pirc and King's Indian positions he keeps misplaying. The original post is a 25-minute read.
The task
The author, a 2200+ blitz player, asked for 5 to 10 recurring positions where his results slip as Black, plus explanations pitched at a 2000 to 2200 player rather than in engine terms. Games were kept if he played Black and the opening was the Pirc, the King's Indian or the Modern, classified by the actual move sequence and not only by chess.com's ECO code. The first prompt asked for a plan before any work, and the session did not start until he said go.
The setup
- A virtual machine with two CPU cores, 4 GB of memory, Stockfish 19 and the python-chess library installed.
- A Claude Code session started with permission prompts switched off.
- A private username file the agent was told never to print, and the instruction to call opponents "White", so the results could be published.
- A progress file in reports/ that he could read from his phone, since the VM's terminal is a web page.
The session ran for four hours and thirteen minutes while his laptop was closed. The VM does not notify on completion unless asked, and he asked for a ping.
The output
The result was an eleven-page PDF brochure: a one-page overview, then one page per position with a diagram from Black's side, the line that reaches it, what he usually plays and how often, what he should play instead, and why. The prompt also asked the agent to say when the engine's reason is not a human reason. The post highlights nine positions. One example is position 6, the Austrian Attack after 6.Be3 Ng4 7.Bg1, where he played 7…e5 in all three games that reached it and the engine prefers 7…c5.
The post also covers the scoring system Claude devised to rank teachable positions and how it calibrated findings to his playing strength.
