The fastest way to find your biggest chess weakness is to analyze a batch of your own recent games with a strong engine and look for the mistake that repeats, not the worst single blunder, but the pattern. Here's how to do it.
A single dramatic blunder is memorable but rare. What actually costs you rating is the small mistake you make in game after game: hanging a piece in the same kind of position, drifting in the middlegame with no plan, or playing the opening too slowly. Finding the pattern is the goal.
Export 20–50 recent games from Chess.com or Lichess. A larger sample makes patterns obvious.
Run each game through Stockfish (depth 20+ for reliable evaluations). Note every move where the evaluation swings against you.
Group them: opening, tactics, middlegame planning, endgame technique, time. Count how often each category appears.
A mistake that shows up in half your games matters far more than a one-time disaster. Rank by frequency × severity.
Pick the single most-frequent pattern and train it deliberately with spaced repetition before moving on.
This is exactly what Mainline does: connect Chess.com or Lichess and it runs the engine, categorizes and ranks your recurring mistakes by rating-point cost, and builds the drill queue for you.