White 249 vs Black 647

The two setups

White: setup #249 N R K B B Q N R

King on the c-file, rooks on b, h, queen on the f-file; no bishop starts in a corner; the knights start away from the centre. The king already stands on a castled square, so one of the castlings moves only the rook. In ordinary symmetric play setup 249 gives White +0.48 (Morozov Balance Index, 400M nodes).

Black: setup #647 R N B K R Q N B

King on the d-file, rooks on a, e, queen on the f-file; one bishop starts in a corner; the knights start on central files. Castling follows the Chess960 rule: king and rook end on the classical squares. In ordinary symmetric play setup 647 gives White +0.15 (Morozov Balance Index, 400M nodes).

Why the pair is balanced

At the deepest rungs (400M, 800M, 1.6B nodes) the evaluation is exactly 0.00 each time, reaching search depth 53.

Admission rule: |cp| ≤ 5 at four budgets up to 4 billion nodes, no one-sided drift along the ladder, and confirmation by two independent engines — Berserk and Lc0 — each below its own median on symmetric positions. The same corridor is required at every deeper budget (8 G, 16 G) at which the pair has been evaluated.

The shallow rungs wandered between -24 and +18 cp before settling — a reminder that quick engine checks overstate imbalances, and why the ladder goes deep.

For comparison, in symmetric play setup 249 gives White +0.48 and setup 647 gives White +0.15: with both sides on the same rank the first move is worth something. In this pair Black's own setup absorbs that edge completely.

The engine's first choice for White is e4; the alternatives are slightly weaker but keep the game level.

Along the engine's main line (30 moves) the largest swing was 33 cp (around move 5), ending at 0 cp — the position stays playable for both sides.

Engine self-play agrees: 10 games, White won 0, drawn 10, Black won 0 (White scored 50.0%).

Verification ladder

Nine independent searches of the starting position, each with a larger node budget. Evaluation in centipawns from White's point of view.

Deep verification

The search ladder reaches 1.6 billion nodes; admission needs a 4-billion rung and two further engines on top of that. Beyond even that, every pair was re-checked at budgets up to ten times larger and in thousands of self-play games. This section shows what each check returned for this pair.

This pair stays within the ±5 cp corridor up to 4 000 000 000 nodes.

Independent engines, run on the same position:

• Berserk 14: 0
• Lc0 0.32.1: +8

Independent confirmations: 3 of 3. An engine counts as confirming when its reading of the pair is closer to equality than its own reading of a typical symmetric Chess960 position (+10 for Berserk, +18 for Lc0). Where only one engine confirms, the pair is balanced according to that engine alone, and this page says so.

Own weight of each setup, measured against the classical array: White +29, Black +67, difference -38. A balanced pair needs White's setup to be weaker by about the price of the first move.

Extended self-play: 10 games, 0 White wins, 10 draws, 0 Black wins, White scored 50.0%.

Best first moves

The 3 best first moves for White, searched together at 400 000 000 nodes.

Main-line play-out

30 moves, 5 000 000 nodes per half-move. Largest |evaluation| 33 cp, mean 6.5 cp, final 0 cp.

Engine self-play

10 games at 500 000 nodes per move: White won 0, drawn 10, Black won 0 — White scored 50.0%. Average length 48.6 moves.

1. f4 f5 2. e3 g6 3. Bf3 Nf6 4. d4 a5 5. c4 Qf7 6. Nc2 O-O 7. Nh3 h6 8. Qd3 Bg7 9. Nf2 d5 10. cxd5 Rd8 11. Bc3 Nxd5 12. Qd2 b6 13. O-O Ba6 14. Rfe1 Bb7 15. e4 fxe4 16. Bxe4 Nd7 17. Rbc1 Nc5 18. Bxd5 Rxd5 19. Qe3 Na4 20. Qxe7 Qxe7 21. Rxe7 Rc8 22. Ne3 Rdd8 23. f5 Nxc3 24. Rxc3 Kf8 25. Rcxc7 Rxc7 26. Rxc7 Bxd4 27. Rxb7 Bxe3 28. Kf1 gxf5 29. Ke2 Bxf2 30. Kxf2 Rd2+ 31. Kg3 Rxb2 32. h4 b5 33. a3 Rb3+ 34. Kf4 b4 35. a4 Ra3 36. Kxf5 Rxa4 37. g4 Ra3 38. Rb5 Kg7 39. Rb7+ Kf8 40. Rb5 Ke7

1. d4 e5 2. dxe5 Nc6 3. e3 g6 4. f4 f6 5. Nf3 fxe5 6. fxe5 Nxe5 7. Nxe5 Bxe5 8. Bf3 Nf6 9. O-O-O Qf7 10. Nb3 O-O 11. Na5 d5 12. Bb4 Re8 13. Bxd5 Nxd5 14. Qxf7+ Kxf7 15. Rxd5 Bf5 16. b3 Bg7 17. Nc4 a6 18. Bc5 Kg8 19. a4 b5 20. Nb2 Be4 21. Rd2 Be5 22. Rf2 Rad8 23. a5 h5 24. b4 h4 25. h3 Kg7 26. Bd4 Bxd4 27. exd4 Rxd4 28. Re1 Bc6 29. Rxe8 Bxe8 30. Nd3 Bc6 31. Nc5 Rxb4 32. Ne6+ Kh6 33. Rf8 Kh7 34. Rf7+ Kh6 35. Rf8 Kh7 36. Rf7+ Kh6

Play it in the CH960 app

Open this page on a phone with the CH960 app installed, or find pair 249 / 647 in the app's encyclopedia, then choose how to play.

• Local game — two players on one device, with a clock.
• With a mentor — a clearly labelled training bot with hints, at your level.
• Challenge a friend — an online game by link; both players get the same pair, colours swap on rematch.

Play this pair against the computer, right here Play a friend

FEN (Shredder, castling rights by rook files): rnbkrqnb/pppppppp/8/8/8/8/PPPPPPPP/NRKBBQNR w BHae - 0 1

Mirror twin: White 617 vs Black 210 — a different position (castling squares are fixed), not evaluated by the search.