Tampermonkey is a popular userscript manager available for browsers like Chrome, Firefox, and Safari. A "chess script" is a small program that lives within this manager and executes only when you visit a specific chess site.
function init() addStyles(); const board = document.querySelector(SITE.boardSelector); if (!board) return; ensureUI(board); highlightLegalMoves(board); highlightLastMove(board); // start a default 10s timer when it's your turn — naive approach; override per-site startMoveTimer(board, 10); // watch for DOM changes to re-run UI additions const obs = new MutationObserver(() => ensureUI(board); highlightLastMove(board); ); obs.observe(document.body, childList:true, subtree:true ); tampermonkey chess script
This is the controversial side of userscripting. Malicious scripts act as a "bridge" between the browser and a local chess engine: Tampermonkey is a popular userscript manager available for