Quick answer
X-Ray Defense is a tactical idea: two aligned attackers on the king file. Work from the first evidence position for X-Ray Defense, and begin by testing e6.
Begin from e6 in 8/4pk2/8/8/8/8/7K/4Q2R b - - 5 3. Start with the forcing geometry: checks, captures, threats, defenders and flight squares around the target. The evidence answer is: X-Ray Defense: preserve the alignment and calculate the defensive interposition before trading the front piece. Candidate line: e6.
In the X-Ray Defense example, notice: side Black; pieces Black pawn e7, Black king f7, White king h2, White queen e1, White rook h1; legal first moves e6, e5, Ke8, Kf8, Kg8, Kg7, Kg6, Kf6. Anchor your reading to the FEN above; the inventory is illustrative, not a portable law of chess.
The tactical trigger
The first evidence board tests two aligned attackers on the king file; the second board tests two aligned attackers on the king file. Where the evidence stores a move string, A is built with direct FEN setup and B with direct FEN setup. Definitions for adjacent ideas are on the Chess Wiki and the Tactics hub. Then compare Candidate Moves with X Ray Attack, Battery, Windmill around the overloaded attacker.
The two inventories make the distinction concrete. A contains side Black; pieces Black pawn e7, Black king f7, White king h2, White queen e1, White rook h1; legal first moves e6, e5, Ke8, Kf8, Kg8, Kg7, Kg6, Kf6; B contains side White; pieces Black pawn e7, Black king f7, White rook e6, White queen c3, White king f1; legal first moves Rxe7+, Rf6+, Rg6, Rh6, Re5, Re4, Re3, Re2. Compare the side to move before comparing the labels in the context of the only defensive interposition.
Topic dossier for this page and board pair r1:8 | r2:4pk2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:7K | r8:4Q2R / r1:8 | r2:4pk2 | r3:4R3 | r4:8 | r5:8 | r6:2Q5 | r7:8 | r8:5K2: start with the overloaded attacker; then test the only defensive interposition; keep the final simplification separate from the last safe flight square; use a counter-check that changes the calculation as the transfer check; and reserve a deflection from the critical square for the exception.
Calculation order
On the first board, calculate e6 after e6 and write down the opponent's best reply around the overloaded attacker. On the second board, calculate Rxe7+ after Rxe7+ and check the only defensive interposition. Calculate the most forcing move first, then test the opponent's best capture, interposition or counter-check before naming the motif. In this case the useful condition is a deflection from the critical square.
Key claim: X-Ray Defense is illustrated here by two aligned attackers on the king file; the first concrete test is e6. The board anchor is 8/4pk2/8/8/8/8/7K/4Q2R; the example is intentionally narrower than the topic label and should not be generalised without checking the surrounding position..
Practical boundary: To answer “How can a player recognize x-ray defense, calculate the winning idea, and test the defender's best resource?”, compare the recorded setup with Rxe7+ and the opponent's reply. The decision is useful only when the stated condition survives that concrete test on board 8/4pk2/4R3/8/8/2Q5/8/5K2. The evidence records Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position and the second board signature r1:8 | r2:4pk2 | r3:4R3 | r4:8 | r5:8 | r6:2Q5 | r7:8 | r8:5K2. The false-positive test is whether the final simplification appears without the last safe flight square, so the conclusion is useful only when the stated condition survives that concrete test.
Evidence positions
example-1: two aligned attackers on the king file
Show answer
X-Ray Defense: preserve the alignment and calculate the defensive interposition before trading the front piece. Candidate line: e6.
Why this position is here: X-Ray Defense is represented by two aligned attackers on the king file. This is a direct FEN setup with board anchor 8/4pk2/8/8/8/8/7K/4Q2R; no opening history is inferred from the diagram.
FEN: 8/4pk2/8/8/8/8/7K/4Q2R b - - 5 3
Question: What is the first concrete decision in this x-ray defense position?
Answer cue: X-Ray Defense: preserve the alignment and calculate the defensive interposition before trading the front piece. Candidate line: e6. The first candidate to test is e6. Replay e6 on board anchor 8/4pk2/8/8/8/8/7K/4Q2R and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
example-2: two aligned attackers on the king file
Show answer
X-Ray Defense: preserve the alignment and calculate the defensive interposition before trading the front piece. Candidate line: Rxe7+.
Why this position is here: X-Ray Defense is represented by two aligned attackers on the king file. This is a direct FEN setup with board anchor 8/4pk2/4R3/8/8/2Q5/8/5K2; no opening history is inferred from the diagram.
FEN: 8/4pk2/4R3/8/8/2Q5/8/5K2 w - - 6 4
Question: What is the first concrete decision in this x-ray defense position?
Answer cue: X-Ray Defense: preserve the alignment and calculate the defensive interposition before trading the front piece. Candidate line: Rxe7+. The first candidate to test is Rxe7+. Replay Rxe7+ on board anchor 8/4pk2/4R3/8/8/2Q5/8/5K2 and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
example-3: two aligned attackers on the king file
Show answer
X-Ray Defense: preserve the alignment and calculate the defensive interposition before trading the front piece. Candidate line: Kc8.
Why this position is here: X-Ray Defense is represented by two aligned attackers on the king file. This is a direct FEN setup with board anchor 8/3kp3/4R3/8/8/8/8/3Q2K1; no opening history is inferred from the diagram.
FEN: 8/3kp3/4R3/8/8/8/8/3Q2K1 b - - 3 2
Question: What is the first concrete decision in this x-ray defense position?
Answer cue: X-Ray Defense: preserve the alignment and calculate the defensive interposition before trading the front piece. Candidate line: Kc8. The first candidate to test is Kc8. Replay Kc8 on board anchor 8/3kp3/4R3/8/8/8/8/3Q2K1 and write down what changes after it.
Evidence boundary: Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position.
Reading the line
Read the first example (id example-1) as a complete record: continuation e6, source fide-laws. This is a direct FEN setup with board anchor 8/4pk2/8/8/8/8/7K/4Q2R; no opening history is inferred from the diagram. If A does not expose two aligned attackers on the king file, correct the evidence before relying on the prose.
Read the second example (id example-2) separately: continuation Rxe7+, source fide-laws. Its feature is two aligned attackers on the king file; inventory side White; pieces Black pawn e7, Black king f7, White rook e6, White queen c3, White king f1; legal first moves Rxe7+, Rf6+, Rg6, Rh6, Re5, Re4, Re3, Re2. Compare what changes between e6 and Rxe7+.
The defensive resource
The main mistake to avoid with X-Ray Defense is spotting a familiar motif but failing to test the defender's strongest legal resource. In A, the missing condition must be located in r1:8 | r2:4pk2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:7K | r8:4Q2R after e6; in B, test it against r1:8 | r2:4pk2 | r3:4R3 | r4:8 | r5:8 | r6:2Q5 | r7:8 | r8:5K2 after Rxe7+.
For X-Ray Defense, the first board's evidence boundary (after e6) is Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position. The second board's evidence boundary for X-Ray Defense is Illustrative evidence for the stated mechanism; it is not a claim that the candidate move is forced or best in every position. If a trusted source or careful calculation changes the conclusion around a counter-check that changes the calculation, update both the evidence record and this article.
Practice from a real game
cover the answer, list checks and captures, and record the defender or escape square that decides whether the idea works. Start with A's side to move and r1:8 | r2:4pk2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:7K | r8:4Q2R; record two candidates, the reply to e6 and the correction. Repeat with B's side to move and r1:8 | r2:4pk2 | r3:4R3 | r4:8 | r5:8 | r6:2Q5 | r7:8 | r8:5K2; the changed board tests transfer rather than diagram memory.
After the drill, compare your notes with X Ray Attack, Battery, Windmill through the last safe flight square. Keep A's rejected alternative beside B's chosen line Rxe7+; this shows whether the conclusion survived a new board signature.
Sources and scope
Sources for X-Ray Defense: 1chess.online editorial scope, FIDE Laws of Chess. Source ids are original-analysis, fide-laws. Primary evidence hook: fide-laws. Comparisons and practice notes are editorial. Evidence revision: 2026-08-remediation-r2.
Scope note for board pair r1:8 | r2:4pk2 | r3:8 | r4:8 | r5:8 | r6:8 | r7:7K | r8:4Q2R / r1:8 | r2:4pk2 | r3:4R3 | r4:8 | r5:8 | r6:2Q5 | r7:8 | r8:5K2: this page does not claim that e6 is an engine principal variation, that an exact endgame result is verified when the evidence says it is not, or that a tool output replaces human calculation. The conclusion is limited to the recorded boundary and the exception the final simplification.