ChessAn X-ray is a rook, bishop or queen whose line is blocked by an enemy piece, yet still "sees" the squares behind it. The moment the blocking piece moves, the line opens, as if the attack went right through it like an X-ray. In any online chess game, when you count captures and trades, you have to count this "through a piece" power too.
What it looks like
Look at this position. White's rook is on d1 and Black's rook is on d5. It seems the white rook is blocked and can't do anything.
The queen on d8 looks unprotected, but she isn't: the rook on d1 has been "watching" d8 through the black rook all along. As soon as the black rook leaves d5 to take the queen, the d-file opens.
Common X-ray shapes
Through an enemy rook
White gives up the queen and gets checkmate in return. The key is that "blocked" d-file: the piece in the way belongs to the opponent, and it has to move.
Along a rank, too
X-rays don't only happen on files. Ranks and diagonals work as well.
A real example: the back rank in the middlegame
In a real game there are many more pieces on the board, and X-rays are harder to see:
Black's rook on d5 is protected by a bishop and a pawn, so it looks solid. If White takes it with a knight or rook, it's just a trade at best. But Black's king has no escape square on the back rank, and the d5 rook happens to stand in front of White's rook, so White has a queen sacrifice that mates. When an enemy piece stands in front of your rook, ask yourself: if I force it to move, what can my rook do?
How to defend
- Give your king an escape square. Push h6 or g6 a little early, so your king has somewhere to go when it's checked. Many X-ray mates then stop working.
- When you count trades, count the pieces behind too. Count every piece on the line, front and back, including the one that's being blocked.
- Don't capture with your only blocker. If your piece is the one blocking your opponent's line, the line opens the moment it leaves.
- Watch which lines the enemy rooks and queen are on. Even with your piece in between, that line can be dangerous.
Practice puzzles
Show answer
1. Qe8+ Qxe8 2. Rxe8# The white queen rushes to e8 with check, and the black queen has to take her from e5. Once the black queen leaves, the e-file opens and the white rook takes back on e8. Checkmate. Simply taking the queen on e5 with the rook is good too, but mate is better.
Show answer
1... Qe1+ 2. Rxe1 Rxe1# The black queen rushes to e1 with check, and White can only take her with the rook on e4. Once the white rook leaves, the e-file opens and the black rook takes back on e1. Checkmate.
Show answer
1. Qe8+ Rxe8 2. Rxe8# The white queen dashes diagonally to e8 with check, and Black can only take her with the rook on e6. With the e-file open, the white rook takes back on e8. Checkmate.
FAQ
How is an X-ray different from a pin or a skewer?
Does an X-ray always involve a sacrifice?
No. The examples above are all queen sacrifices that mate, but often an X-ray just gives you one more defender. For example, in a trade your opponent thinks a square has only one attacker, when really you have another piece behind it watching through his.
How do I practice seeing X-rays?
Every time a rook, queen or bishop has its line blocked by an enemy piece, ask yourself: "If that piece moves, what does this line hit?" Ask it often enough and you'll start seeing them naturally.
Try it yourself
X-rays often show up with skewers and pins, so look at a few more in chess tactics. To try it for real, play chess for free against the computer and keep an eye on whether the back ranks have escape squares.