Quick answer
Active King in Rook Endings is an endgame technique: Lucena bridge-building. Work from the first evidence position for Active King in Rook Endings, and begin by testing Kg7.
Begin from Kg7 in 7k/2P4r/8/1K6/8/8/8/1R6 b - - 5 3. Count the material, king routes, promotion squares and reserve tempi before applying a theoretical rule. The evidence answer is: Active King in Rook Endings: use the king's shelter and a checking-distance bridge before advancing the pawn. Candidate line: Kg7.
In the Active King in Rook Endings example, notice: side Black; pieces Black king h8, White pawn c7, Black rook h7, White king b5, White rook b1; legal first moves Kg7, Kg8, Rh6, Rh5+, Rh4, Rh3, Rh2, Rh1. The listed material and candidate moves belong only to this FEN example and should not be generalised.
Material and result question
The first evidence board tests Lucena bridge-building; the second board tests Lucena bridge-building. Board A’s recorded route is direct FEN setup. Board B’s recorded route is direct FEN setup. Cross-check wording on the Chess Wiki and on the Endgames hub. Then compare Material Values with Rook Endgame Side Checks, Four Rook Endgame Principles, Queen Versus Pawn around king opposition on the critical file.
The two inventories make the distinction concrete. A contains side Black; pieces Black king h8, White pawn c7, Black rook h7, White king b5, White rook b1; legal first moves Kg7, Kg8, Rh6, Rh5+, Rh4, Rh3, Rh2, Rh1; B contains side Black; pieces Black king h8, White king c6, White bishop e6, Black rook h3, White rook a1; legal first moves Kh7, Kg7, Rh4, Rh5, Rh6, Rh7, Rh2, Rh1. Compare the side to move before comparing the labels in the context of the king's route around a pawn chain.
Topic dossier for this page and board pair r1:7k | r2:2P4r | r3:8 | r4:1K6 | r5:8 | r6:8 | r7:8 | r8:1R6 / r1:7k | r2:8 | r3:2K1B3 | r4:8 | r5:8 | r6:7r | r7:8 | r8:R7: start with king opposition on the critical file; then test the king's route around a pawn chain; keep the moment to trade the last pawn separate from a knight route that changes the blockade; use a theoretical draw with practical tests as the transfer check; and reserve a stalemate resource for the exception.
Conversion or defense plan
On the first board, calculate Kg7 after Kg7 and write down the opponent's best reply around king opposition on the critical file. On the second board, calculate Kh7 after Kh7 and check the king's route around a pawn chain. Separate the practical conversion question from the result question; side to move and one checking distance can change the conclusion. In this case the useful condition is a stalemate resource.
Key claim: Active King in Rook Endings is illustrated here by Lucena bridge-building; the first concrete test is Kg7. The board anchor is 7k/2P4r/8/1K6/8/8/8/1R6; the example is intentionally narrower than the topic label and should not be generalised without checking the surrounding position..
Practical boundary: To answer “What exact king, pawn, and move-order conditions decide active king in rook endings, and how should each side play them?”, compare the recorded setup with Kh7 and the opponent's reply. The decision is useful only when the stated condition survives that concrete test on board 7k/8/2K1B3/8/8/7r/8/R7. The evidence records No tablebase outcome is asserted by this generated record; verify the exact FEN before publication and the second board signature r1:7k | r2:8 | r3:2K1B3 | r4:8 | r5:8 | r6:7r | r7:8 | r8:R7. The false-positive test is whether the moment to trade the last pawn appears without a knight route that changes the blockade, so the conclusion is useful only when the stated condition survives that concrete test.
Evidence positions
example-1: Lucena bridge-building
Show answer
Active King in Rook Endings: use the king's shelter and a checking-distance bridge before advancing the pawn. Candidate line: Kg7.
Why this position is here: Active King in Rook Endings is represented by Lucena bridge-building. This is a direct FEN setup with board anchor 7k/2P4r/8/1K6/8/8/8/1R6; no opening history is inferred from the diagram.
FEN: 7k/2P4r/8/1K6/8/8/8/1R6 b - - 5 3
Question: What is the first concrete decision in this active king in rook endings position?
Answer cue: Active King in Rook Endings: use the king's shelter and a checking-distance bridge before advancing the pawn. Candidate line: Kg7. The first candidate to test is Kg7. Replay Kg7 on board anchor 7k/2P4r/8/1K6/8/8/8/1R6 and write down what changes after it.
Evidence boundary: No tablebase outcome is asserted by this generated record; verify the exact FEN before publication.
example-2: Lucena bridge-building
Show answer
Active King in Rook Endings: use the king's shelter and a checking-distance bridge before advancing the pawn. Candidate line: Kh7.
Why this position is here: Active King in Rook Endings is represented by Lucena bridge-building. This is a direct FEN setup with board anchor 7k/8/2K1B3/8/8/7r/8/R7; no opening history is inferred from the diagram.
FEN: 7k/8/2K1B3/8/8/7r/8/R7 b - - 2 2
Question: What is the first concrete decision in this active king in rook endings position?
Answer cue: Active King in Rook Endings: use the king's shelter and a checking-distance bridge before advancing the pawn. Candidate line: Kh7. The first candidate to test is Kh7. Replay Kh7 on board anchor 7k/8/2K1B3/8/8/7r/8/R7 and write down what changes after it.
Evidence boundary: No tablebase outcome is asserted by this generated record; verify the exact FEN before publication.
example-3: Lucena bridge-building
Show answer
Active King in Rook Endings: use the king's shelter and a checking-distance bridge before advancing the pawn. Candidate line: Ra8+.
Why this position is here: Active King in Rook Endings is represented by Lucena bridge-building. This is a direct FEN setup with board anchor 6k1/2P5/8/R1K5/8/7r/8/8; no opening history is inferred from the diagram.
FEN: 6k1/2P5/8/R1K5/8/7r/8/8 w - - 6 4
Question: What is the first concrete decision in this active king in rook endings position?
Answer cue: Active King in Rook Endings: use the king's shelter and a checking-distance bridge before advancing the pawn. Candidate line: Ra8+. The first candidate to test is Ra8+. Replay Ra8+ on board anchor 6k1/2P5/8/R1K5/8/7r/8/8 and write down what changes after it.
Evidence boundary: No tablebase outcome is asserted by this generated record; verify the exact FEN before publication.
Reading the line
Read the first example (id example-1) as a complete record: continuation Kg7, source tablebase. This is a direct FEN setup with board anchor 7k/2P4r/8/1K6/8/8/8/1R6; no opening history is inferred from the diagram. If A does not expose Lucena bridge-building, correct the evidence before relying on the prose.
Read the second example (id example-2) separately: continuation Kh7, source tablebase. Its feature is Lucena bridge-building; inventory side Black; pieces Black king h8, White king c6, White bishop e6, Black rook h3, White rook a1; legal first moves Kh7, Kg7, Rh4, Rh5, Rh6, Rh7, Rh2, Rh1. Compare what changes between Kg7 and Kh7.
Boundary cases
The main mistake to avoid with Active King in Rook Endings is applying a remembered endgame rule while ignoring side to move, king placement or an unverified result. In A, the missing condition must be located in r1:7k | r2:2P4r | r3:8 | r4:1K6 | r5:8 | r6:8 | r7:8 | r8:1R6 after Kg7; in B, test it against r1:7k | r2:8 | r3:2K1B3 | r4:8 | r5:8 | r6:7r | r7:8 | r8:R7 after Kh7.
For Active King in Rook Endings, the first board's evidence boundary (after Kg7) is No tablebase outcome is asserted by this generated record; verify the exact FEN before publication. The second board's evidence boundary for Active King in Rook Endings is No tablebase outcome is asserted by this generated record; verify the exact FEN before publication. If a trusted source or careful calculation changes the conclusion around a theoretical draw with practical tests, update both the evidence record and this article.
Practice from a real game
play the position for both sides, record the critical tempo, and verify the exact FEN against the cited tablebase before publication. Start with A's side to move and r1:7k | r2:2P4r | r3:8 | r4:1K6 | r5:8 | r6:8 | r7:8 | r8:1R6; record two candidates, the reply to Kg7 and the correction. Repeat with B's side to move and r1:7k | r2:8 | r3:2K1B3 | r4:8 | r5:8 | r6:7r | r7:8 | r8:R7; the changed board tests transfer rather than diagram memory.
After the drill, compare your notes with Rook Endgame Side Checks, Four Rook Endgame Principles, Queen Versus Pawn through a knight route that changes the blockade. Keep A's rejected alternative beside B's chosen line Kh7; this shows whether the conclusion survived a new board signature.
Sources and scope
Sources for Active King in Rook Endings: Syzygy tablebase verification reference, 1chess.online editorial scope. Source ids are tablebase, original-analysis. Primary evidence hook: tablebase. Comparisons and practice notes are editorial. Evidence revision: 2026-08-remediation-r2.
Scope note for board pair r1:7k | r2:2P4r | r3:8 | r4:1K6 | r5:8 | r6:8 | r7:8 | r8:1R6 / r1:7k | r2:8 | r3:2K1B3 | r4:8 | r5:8 | r6:7r | r7:8 | r8:R7: this page does not claim that Kg7 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 moment to trade the last pawn.