A lot of AI chess tools play against you or annotate a single game. BlackboxChess does something different: it runs Stockfish across your last 10 to 100 games, classifies every significant error by type, and ranks the results by how much each pattern costs you. The output is a diagnosis, not a blunder log.
The analysis uses Stockfish for move evaluation, then a classification layer that groups flagged positions into recurring mistake types across categories including material loss, king safety, piece activity, pawn structure, and endgame technique.
Every finding is engine-verified. The position was objectively good, you played a specific category of move, and it cost you a measurable amount. There's no guessing. The scoring reflects actual impact per occurrence, not just frequency.
After a rough game it's tempting to run it through an engine and find the blunder. But one game is noisy. You might have dropped a piece because you were tired, or because your opponent found a tactic you hadn't seen. That's not the same as a structural weakness.
The signal worth having comes from patterns across many games. When the same mistake type shows up regardless of opening, opponent, or time control, that's something you can train against. That's what this analysis surfaces.
The $10 full report includes a short drill course generated from your actual games. Positions come from your own game history — real situations where your top weakness appeared. About 10 drills. Short enough to actually do; targeted enough to be useful.
Knowing what you do wrong is step one. The course is step two.
Free tier: 10 games, your top mistake type, no account needed. Full report at $10: 100 games, all patterns ranked, three game examples per pattern with move-by-move context, and the fix course. If the engine analysis is factually wrong, refund issued.
"It shocked me at first to see what even your website showed, some of it I immediately realised as having been areas to improve on from my intuition of what's lacking but most of these are seriously incisive insights past what players like myself can recognise."
BlackboxChess user
"I can say that after trying, trusting and testing BlackboxChess, I am quite better for it and grateful. You've earned a serious fan of your work."
BlackboxChess user
"Got my three weaknesses already — back rank blunders, unnecessary queen trades, losing my advantage."
Chess.com player, ~1200 Elo