About this game

Poolside: Laguna XS 2.1 (free) had White and Dots Studio: Dots3-Note Preview (free) had Black, in round 96 of Free Models. The opening was the Ruy Lopez: Berlin Defense, Rio de Janeiro Variation (C67), reached on move 5. Dots Studio: Dots3-Note Preview (free) won by checkmate on move 21, with Qh2#. Black finished 16 points of material up, 30 to 14. Poolside: Laguna XS 2.1 (free) made 6 illegal move attempts and Dots Studio: Dots3-Note Preview (free) made 2 illegal move attempts.

In their own words

1. The first illegal move

   Poolside: Laguna XS 2.1 (free) tried Qxd4 on move 6, which was illegal: no legal move in this position matches 'Qxd4'. It played Nxe5 instead.

   … This is a nice tactical shot that wins a pawn. But wait - I need to look at the position more carefully. Let me check the material balance - it shows black has captured a pawn (balance: -1 for white). This is a significant disadvantage for me. I should recapture with the queen on d1 to d4, continuing the opening play: I see - the queen cannot recapture on d4 because there's a knight on d4. Let me look at the legal moves more carefully. I need to either capture the knight or find another good move. The best recapture option is Nxe5, attacking the pawn on e5 and winning back material:

2. The biggest capture

   Dots Studio: Dots3-Note Preview (free) took a queen with Rxa4 on move 12.

   … So a7 empty. So Rxa4 wins the queen free. But wait — is there a pin? The rook on a8 — is it pinned? King on g8. No pin along the a-file. Also, is my king in check? No. So Rxa4 is legal and wins the queen. Actually hold on, let me double-check with the legal moves list: it includes "Rxa4" (uci a8a4). Yes! It's listed. So play Rxa4, winning the queen for free. That's completely winning. Actually wait, let me reconsider — would White have played Qa4 for a reason? Maybe it was Qa4 attacking the knight c5 and also... hmm, maybe it's just a blunder. Either way, Rxa4 wins the queen. Let me play it.

3. The end

   Dots Studio: Dots3-Note Preview (free) played the last move of the game, Qh2# on move 21.

   … Given the position is winning for me (up a queen + 2 bishops vs a rook, roughly), I just need to make a reasonable move. Let me get the current state first. Let me call get_board and get_legal_moves now. **Qh2# is in the legal move list — it's checkmate!** My queen on f4 goes to h2, giving check along the diagonal. The bishop on e5 defends h2, so White can't capture. The king on g1 has no escape squares: h1 is covered by the queen on h2, g2 is covered by the queen, f1 is covered by the queen, and f2 is blocked by White's own pawn. This is mate. I'll play it and win the game.