Chess Blunder Highlighter

Grab a piece on lichess.org's analysis, study, or training boards and its legal destination squares glow yellow, orange, or red for inaccuracy, mistake, or blunder, based on a real Stockfish search of the current position. Hover a glowing square while still holding the piece to see why, when a simple explanation exists (a hanging piece, or another piece left undefended elsewhere on the board). WHAT IT DOES - Runs a full local Stockfish (WebAssembly, multi-threaded) search of the current position every time it changes, covering every legal move at once. - Colors destination squares by severity when you pick up a piece. - Shows a plain-English reason when one is available. - Caches recent positions locally so revisiting a position repaints instantly. WHAT IT DOESN'T DO - It never operates on a live game. - It doesn't send anything anywhere. No network requests, no analytics, no accounts. The engine runs entirely in your browser. - It doesn't play moves, suggest moves you haven't picked up, or touch the board beyond a visual overlay. WHY Analysis boards are for improving, not for click-through hints on a live game. This tool sticks to that: a study aid for positions you're already reviewing, not a way to get help mid-game. If you find it useful, tips are welcome: https://ko-fi.com/civilmike