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Calculation: The Blunder Check

The blunder check is a final safety check before you move. Ask what the move hangs, what check it allows, and what fork it allows.

A blunder that loses a queen

The queen captures the pawn on f7. The king captures the queen, because the queen is undefended. The blunder check asks whether the queen is defended before the capture, and here it is not.

FEN: 4k3/5p2/8/7Q/8/8/8/6K1 w - - 0 1

a b c d e f g h
8 . . . . k . . . 8
7 . . . . . p . . 7
6 . . . . . . . . 6
5 . . . . . . . Q 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 . . . . . . K . 1
  a b c d e f g h

A blunder that allows a fork

The rook captures the pawn on a7. The knight jumps to c7 and gives check to the king on d5, attacking the bishop on e6. The blunder check asks whether a capture allows a fork, and here it does.

FEN: 7k/p7/R3B3/1n1K4/8/8/8/R7 w - - 0 1

a b c d e f g h
8 . . . . . . . k 8
7 p . . . . . . . 7
6 R . . . B . . . 6
5 . n . K . . . . 5
4 . . . . . . . . 4
3 . . . . . . . . 3
2 . . . . . . . . 2
1 R . . . . . . . 1
  a b c d e f g h

Key points

  • A blunder check happens after you choose a move, before you play it.
  • Ask whether the move hangs a piece.
  • Ask whether the move allows a check.
  • Ask whether the move allows a fork, pin, or discovered attack.
  • Ask whether the move lets the opponent capture for free.
  • A blunder check takes a few seconds and saves many games.
  • A blunder check is a habit, not a calculation.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Rust Playground

Exercise

White to move. Which move is a blunder that loses the queen?