White 257 vs Black 353

The two setups

White: setup #257 B N R B K N Q R

King on the e-file, rooks on c, h, queen on the g-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 257 gives White +0.25 (Morozov Balance Index, 400M nodes).

Black: setup #353 B N R B K R Q N

King on the e-file, rooks on c, f, queen on the g-file; one bishop starts in a corner; the knights start away from the centre. Castling follows the Chess960 rule: king and rook end on the classical squares. In ordinary symmetric play setup 353 gives White +0.25 (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 59.

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 agreed early: from 100 thousand to 128 million nodes the evaluation never left ±13 cp.

For comparison, in symmetric play setup 257 gives White +0.25 and setup 353 gives White +0.25: with both sides on the same rank the first move is worth something. In this pair Black's own setup absorbs that edge completely.

White is not forced into a single path: the best first move is b3, and 3 first moves are within 10 cp of it.

Along the engine's main line (30 moves) the evaluation stayed within ±24 cp the whole way: the balance holds as the pieces come out, not only on move one.

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: -4
• Lc0 0.32.1: +4

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 +15, Black +42, difference -27. 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| 24 cp, mean 14.0 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 47.7 moves.

1. f4 b6 2. Qf2 f5 3. b3 e6 4. e3 Nf7 5. h4 Bf6 6. Bxf6 gxf6 7. Rg1 Nc6 8. g4 fxg4 9. Bxg4 f5 10. Bf3 Qh8 11. Nc3 O-O-O 12. O-O-O Rg8 13. Nh2 Rxg1 14. Rxg1 Rg8 15. Rxg8+ Qxg8 16. Qg2 Qxg2 17. Bxg2 Bb7 18. Nb5 Kb8 19. d3 Nh6 20. Nc3 Ng8 21. Kd2 Nf6 22. Nd1 b5 23. a3 Ne7 24. Bxb7 Kxb7 25. Nf3 c5 26. c4 bxc4 27. bxc4 Kc6 28. Nc3 d6 29. Nb5 a6 30. Nc3 h6 31. Ne2 Kb6 32. Nc3 Ng6 33. Ne2 Nh5 34. Kd1 Kc7 35. Nc3 Kd7 36. Ke2 Nf6 37. Na4 h5 38. Kd1 Kc6 39. d4 cxd4 40. Nxd4+ Kd7 41. Nb6+ Kc7 42. Na4 Nf8 43. Kc2 Ne4 44. Nc3 Nc5 45. Nf3 Ng6 46. Ne2 Ne4 47. Ng5 Kd7 48. Nxe4 fxe4 49. Ng3 Nxh4 50. Nxe4 Nf5 51. Nf6+ Ke7 52. Nxh5 Nxe3+ 53. Kd3 Nf5 54. Ke2 a5 55. Kf2 Nd4 56. Ng3 Kd7 57. a4 Nb3 58. Ne4 Kc6 59. Ke3 Nc5 60. Nc3 Kc7 61. Nb5+ Kd7

1. e3 b6 2. b3 e6 3. h4 f5 4. Be2 Be7 5. O-O-O O-O-O 6. Nc3 Nf7 7. d4 Nc6 8. Kb1 g6 9. f3 d5 10. g4 fxg4 11. fxg4 Kb8 12. g5 e5 13. Bb2 e4 14. Bg4 Nd6 15. Ng3 Bb7 16. Nge2 Nf5 17. Rf1 Bc8 18. Bh3 Nxh4 19. Rxf8 Bxf8 20. Bxc8 Nf3 21. Qg4 Rxc8 22. Nf4 Ne7 23. Nfxd5 Nd2+ 24. Kc1 Nxd5 25. Nxd5 Qxd5 26. Kxd2 Bd6 27. Rxh7 Rf8 28. Rh4 Qa5+ 29. Bc3 Rf2+ 30. Ke1 Qxc3+ 31. Kxf2 Qxc2+ 32. Kg1 Qb1+ 33. Kg2 Qc2+ 34. Kh1 Qb1+ 35. Kg2 Qxa2+ 36. Kf1 Qb1+ 37. Kg2 Qb2+ 38. Kf1 Qc1+ 39. Kf2 Qd2+ 40. Kf1 Qd3+

Play it in the CH960 app

Open this page on a phone with the CH960 app installed, or find pair 257 / 353 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): bnrbkrqn/pppppppp/8/8/8/8/PPPPPPPP/BNRBKNQR w CHcf - 0 1

Mirror twin: White 603 vs Black 315 — a different position (castling squares are fixed), not evaluated by the search.