Knight's Tour — free browser game

You control a chess knight. First pick a starting square, then on every move the knight jumps in an 'L' shape (two squares one way, one square perpendicular). Your goal: visit every square on the board exactly once. You can't revisit a cell; legal moves are marked with green dots. Visit them all to complete the tour; run out of legal moves and the round ends. The 5/6/7/8 buttons up top change the board size — small is easy, big is hard. Tip (Warnsdorff's heuristic): on every move, prefer the square that itself has the **fewest onward moves**; deal with corners and walls early and save the centre for last.