ChessDrills

ChessDrills shows which of your openings cost you rating, from any Chess.com or Lichess username, free and without signup. It reads the last 300 finished games (up to 150 as White and 150 as Black) by colour and time control, and marks the openings where the player scores below what the ratings predict, so it's clear which ones to fix first. Openings with only a few games are marked as a small sample. The same report shows a style profile: how often the player is out of book by move 3, fianchettos, plays open, semi-open or closed centres, castles on opposite sides and gets into time trouble. It also finds the endgame moves that turned a win into a draw or a draw into a loss. Each opening can then be practised against an AI matched to the player's rating, and Stockfish reviews the game, marking inaccuracies, mistakes and blunders and showing the best move.

More free tools:

• Opening plan (Lichess): what to play instead of your weakest openings, from your last 300 games compared with players of your rating.
• Prepare: enter your username and your opponent's to see which openings to play and which to avoid.
• Top players: the most played openings of the 50 top-rated Chess.com blitz players, such as Hikaru Nakamura and Magnus Carlsen, plus GothamChess and Anna Cramling, from 300 recent blitz games each, updated daily.
• Did I play a cheater?: how many rating points you lost to opponents who were later banned for cheating. It runs in your browser and reads only public games.

No account, no card, nothing to install. Only a username is needed, never a password. Every report is a link you can share with a coach or a friend.