Datasets:
puzzle_id stringlengths 5 5 | rating int64 399 999 | bucket stringclasses 1
value | fen stringlengths 30 73 | prompt listlengths 2 2 | completion stringlengths 431 1.96k | expected_moves listlengths 1 1 |
|---|---|---|---|---|---|---|
DrUVA | 929 | beginner | r5k1/pp3q2/2p5/3bB3/3P1p2/P1P4R/4R3/6K1 w - - 1 34 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is hemmed in by its own queen on f7. My bishop on e5 controls the long diagonal through empty f6 and g7 to h8, and the h3-rook has a fully open h-file. This points to back-rank mate. I first considered the tempting check Rg2+. After Kf8 my Rh8+ allows Ke7 where the king slips away, as neither my bish... | [
"h3h8"
] |
NnCPb | 462 | beginner | 3r4/ppp2p2/2b3pk/b3N2p/8/8/PB3PPP/RN4K1 b - - 1 25 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black to move with my king safe on h6 and white's king on g1. I have a material edge with two bishops and a rook against white's minor pieces, but the open d-file from my Rd8 is the key motif as white's first rank is vulnerable with only Ra1 and Nb1 defending and e1/f1 empty.
One tempting try is Be8 (from c6) hoping t... | [
"d8d1"
] |
1tFSJ | 948 | beginner | r5k1/5ppp/p1n5/1p6/3PQ3/2P2Pb1/PPB2P1q/RNB2K2 b - - 7 22 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White king on f1 is shielded only by the f2-pawn. My queen on h2 attacks f2 along the second rank, my bishop on g3 attacks f2 diagonally, and nothing else defends it. White's queen on e4 and bishop on c2 do not protect the spot.
I first consider Qh1+ checking along the first rank, but Ke2 lets the king escape and Whit... | [
"h2f2"
] |
2z9T7 | 908 | beginner | 5rk1/R4p1p/2p3p1/2n2N2/6P1/2Bn4/5PKP/8 w - - 0 30 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | The black king is on g8, trapped behind its rook on f8 and pawns on f7, g6, h7. My knight on f5 is well placed to check, the bishop on c3 controls the diagonal to g7 and h8, and the rook on a7 commands the seventh rank. This looks like a mating net if I can find the right check.
I first consider moving the knight to d6... | [
"f5h6"
] |
kZvky | 898 | beginner | r1b2rk1/pp2ppbp/3p2p1/8/2N1PPn1/2PQ1nPP/PP4B1/R1B3RK b - - 0 15 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king on h1 is trapped by its own rook on g1 and bishop on g2, while my knight on f3 covers the h2 flight square and my knights on f3 and g4 swarm the area. I first consider Ne1 with the f3 knight, but White plays Qe2 and after Nxg2 hxg4 I lose a knight for nothing with no attack left. Next I examine Nxg1 with t... | [
"g4f2"
] |
Yk6Ax | 950 | beginner | r1b2rk1/pp4pp/2p1p3/2Pp1p2/1P1Pn1Nq/P1N1P3/1BQ1BbPP/R4R1K b - - 0 15 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is hemmed in on h1 by its own pawns on g2 and h2. I have a queen on h4, bishop on f2, and knight on e4 all aimed at the kingside, with the h2-pawn pinned to the king along the open h3 square.
First I look at the tempting Qxh2+, capturing the pawn with check. But the king takes it with Kxh2, and nothing de... | [
"e4g3"
] |
Yle7m | 955 | beginner | 3Q1bk1/5p1p/6pq/4N2n/8/1P3P2/P5PP/6NK b - - 0 29 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White king on h1 is trapped by its own knight on g1 and pawns on g2 and h2 with no flight squares. My queen on h6 lines up on the h-file behind the h2-pawn and my knight on h5 can reach g3. A tempting try is f6 attacking the e5-knight but white gets Qd5+ forcing my king to g7 and then g4 leaving me worse. Qg7 looks def... | [
"h5g3"
] |
V9t2o | 585 | beginner | r1b1k2r/1pqpBppp/p3p3/8/P3P1n1/1BN5/1PPQ1PPP/R4RK1 b kq - 0 13 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: White's king sits on g1 with my knight on g4 nearby, the h2-pawn defended solely by that king, and my queen on c7 aiming along the empty c7-d6-e5-f4-g3-h2 diagonal. The white bishop on e7 looks tempting but may expose my king. Kxe7 seems greedy but after Qg5+ Nf6 e5 my king is stuck in the center an... | [
"c7h2"
] |
PVXAc | 713 | beginner | 8/8/P1R5/5P2/2bp2P1/2kp2P1/2p5/2K5 b - - 0 45 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king sits on c1 with my king on c3, pawn on c2, and bishop on c4 all nearby while my d3-pawn can advance. White's a6-pawn and c6-rook mean I cannot afford a slow move. I first consider Kb4 to step away and support my pawns, but White replies a7 and after my Kc3 the rook takes my bishop with check, letting the a... | [
"d3d2"
] |
Xj5rZ | 927 | beginner | r2q1rk1/1ppb2p1/p2b1n2/3Np1p1/2Bp3Q/1P6/P4PPP/B3R1K1 w - - 0 20 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: black king on g8 is hemmed in by its own Rf8 and Pg7, my Qh4 controls the open h-file to h7 and h8, and my Bc4 aims at g8 along the diagonal but is blocked by my own Nd5. Any Nd5 move will unmask discovered check from the bishop.
Ne3+ is a tempting check but after Rf7 my Qxg5 is met by b5 and the p... | [
"d5f6"
] |
T1XIY | 574 | beginner | r1bqk2r/pppp1p2/7p/b7/1nP1N1p1/P4NB1/4PPPP/R2QKB1R b KQkq - 0 12 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Looking at the white king on e1, I notice the bishop on a5 is aimed straight down the a5-e1 diagonal, currently blocked only by my own knight on b4. That means any knight move from b4 is a discovered check from the bishop — the squares c3 and d2 in between are empty. So I'm looking for the knight move that finishes the... | [
"b4c2"
] |
DX6wC | 819 | beginner | 8/3P4/p1pk4/3p4/1P1K2Br/8/1P6/8 w - - 10 45 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My d7-pawn is one step from promotion with the black king on d6 right in front, and my g4-bishop is hanging to the h4-rook but it's my move. I first consider Kc3 to get active, but Black replies Ke7 and my bishop falls while the rook activates on the h-file with no immediate mate. Ke3 looks similar allowing Ke7 and Rh8... | [
"d7d8q"
] |
BC2P4 | 815 | beginner | 6k1/p4pbp/3p4/1Pp2p2/P4P2/5NP1/1r3K1P/1R6 w - - 0 27 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | First, I notice Black's rook on b2 is attacking my rook on b1 down the file, and my rook is undefended — the king on f2 doesn't reach b1, nothing else covers it. So my rook is hanging and I have to address that immediately. Any quiet king move like Ke3, Ke1, or Kf1 just lets ...Rxb1 collect the rook (and from e1 or f1 ... | [
"b1b2"
] |
w2w5q | 901 | beginner | 5Q2/1kq5/R1p1r1p1/5p1p/P7/6PP/5P1K/8 w - - 3 47 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king is cramped on b7 next to its queen on c7 and pawn on c6. My rook on a6 cuts off the a-file and sixth rank, while my queen on f8 can access the eighth rank. I look for a knockout blow.
First I consider Qb4+. It checks along the b-file, but the king can capture my rook with Kxa6. Then after Qc4+ Ka5 I'm down... | [
"f8a8"
] |
H7vJN | 422 | beginner | 1r6/k4ppp/1q2n3/2p5/p1Q3P1/P4P1P/1PP2B2/1K2R3 b - - 6 35 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Looking at the b-file: my queen on b6, my rook on b8, and the white king sitting on b1 with just a pawn on b2 between us. That's a battery already pointing straight at the king. Qxb2+ jumps out — the queen takes the pawn and checks from right next to the king. Is it defended? My rook on b8 looks down the file through b... | [
"b6b2"
] |
V15xZ | 748 | beginner | r4rk1/2p2p1p/2p1N3/3p1qp1/3Bp1n1/P3P1PB/2PP1P1P/R2QK2R b KQ - 0 18 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is still on e1 in the center. I have a knight on g4 attacking f2, where white has a pawn defended only by the king. Qd1 does not attack f2, the e3 pawn blocks Bd4 from f2, and Bh3 cannot reach f2 on its diagonal. Qxf2 is tempting. Nxe3 is flashy but after Bh3xf5 my knight takes back on f5 and white's Qd1xg... | [
"f5f2"
] |
S0ugx | 667 | beginner | rnb1rq1k/pp3p1p/5p2/3Pp3/7Q/1N1B4/PPP3PP/R5K1 w - - 0 19 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king sits on h8 blocked by its queen on f8, rook on e8, and lone pawn on h7. My queen on h4 stares down the h-file at that pawn while my bishop on d3 aims at h7 along the clear e4-f5-g6 diagonal. Qxh7+ looks promising, but I must check alternatives. Bxh7 takes the pawn but does not check the king on h8 because ... | [
"h4h7"
] |
ExqCS | 979 | beginner | 1r1qkb1r/pp1bn3/2pp4/3Np2p/6pP/1Q1BP3/PPP2PP1/2KR2NR w k - 0 15 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king sits on e8 boxed in by its queen on d8, bishop on d7, knight on e7 and bishop on f8, with only f7 as a possible flight square. My Nd5 is ready to jump and my Qb3 eyes the long diagonal that runs through d5 to f7.
Nxe7 looks tempting as it grabs the knight, but a knight on e7 does not attack e8 so it is not... | [
"d5f6"
] |
y7VGX | 954 | beginner | r1bqkb1r/1p1pnp1p/p1n1p1p1/1Np5/2B1P3/P4Q2/1PPP1PPP/R1B1K1NR w KQkq - 0 7 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on e8 is boxed in by its own pieces: queen on d8, knight on e7, bishop on f8, and pawns on d7 and f7 — every adjacent square is occupied by a friendly piece. That instantly screams knight mate, since a knight check can't be blocked. My knight on b5 can leap to d6, and from d6 it attacks e8. Tempting altern... | [
"b5d6"
] |
buALi | 799 | beginner | rnb1k2r/pp3ppp/1qp5/3pN3/4n3/3B4/PPPP2PP/RNBQ1K1R b kq - 3 9 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king on f1 is exposed with only the g2-pawn and Nb1 nearby. My Ne4 is hanging to the Bd3, so I first consider Nd7 to defend it, but then Bxe4 dxe4 Nxd7 leaves me worse with no attack. O-O is a natural developing move, yet Bxe4 dxe4 Nc3 lets White stabilize and trade off my active pieces. Qd4 attacks the Ne5 but... | [
"b6f2"
] |
b7I7k | 870 | beginner | rn2kb1r/ppp2pp1/4p2p/3pNb2/4nP1q/1P1BP3/PBPP2PP/RN1Q1K1R b kq - 5 8 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king on f1 is boxed in by its own Qd1, Rh1, and pawns, with no castling left. My Qh4, Ne4, and Bf5 create a direct mating pattern on the weakened light squares and first rank. The knight on e4 already eyes f2 right next to the king, so I scan for forcing moves.
Ng3+ looks flashy, forking the king and Rh1. Aft... | [
"h4f2"
] |
5FOsf | 666 | beginner | 1N3kr1/2p5/b4p2/p6n/2q5/5R1P/P4PPQ/5RK1 b - - 0 27 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Let me look at what Black has. My queen on c4 and my bishop on a6 both bear down the a6-f1 diagonal toward White's back rank; with the queen on c4 stepping off that diagonal, the bishop covers f1 directly. The white king on g1 has very little air — f2 and g2 are its own pawns, h1 is empty but the queen on h2 sits there... | [
"c4f1"
] |
kpCtj | 951 | beginner | rnbqkb1r/1p1ppp1p/p4np1/1N6/8/4Q3/PPPP1PPP/R1B1KBNR w KQkq - 0 7 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I see my knight on b5 is attacked by the black pawn on a6. The black king on e8 has no escape squares because its own queen occupies d8, bishop occupies f8, and pawns occupy d7, e7, and f7. First I consider the tempting Nc7+ for an immediate knight check. Black simply takes Qd8xc7 and nothing recaptures on c7, so I los... | [
"b5d6"
] |
wdxE5 | 668 | beginner | 4n1k1/q5p1/6Bp/p7/2p5/2P2K2/P6P/4R3 w - - 0 35 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: black king on g8 is hemmed by its own pawns on g7 and h6 with only the knight on e8 nearby, my bishop on g6 controls e8 f7 and h7, and my rook on e1 has a clear path up the open e-file while black's queen on a7 is far from the action. First I consider the greedy capture Bxe8 but after Qc5 I have to ... | [
"e1e8"
] |
gNPCU | 852 | beginner | 5rk1/5pp1/p1R5/1p1PpN2/3bP1Q1/1P3K1P/1q4P1/8 b - - 8 36 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king on f3 is exposed, and my queen on b2 combined with the bishop on d4 controls the dark squares around it, with the bishop covering e3 and f2. Qxb3+ is tempting but after Ke2 the king escapes and I have no strong follow-up. Qxg2+ loses the queen for just a pawn since the queen on g4 captures safely on g2. Qe... | [
"b2f2"
] |
dYk14 | 559 | beginner | 2r1k2r/3p1ppp/Q3p3/P1bnP1B1/1p6/8/1Pq2PPP/RN2R1K1 w k - 2 17 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black king sits on e8 with his rook on c8 and queen on c2 while my queen on a6 eyes c8 via the empty b7 diagonal. I have more active pieces and an advanced e5-pawn but must act before he coordinates. First I look at Nb1-c3 attacking his queen but he has Qxf2+ Kh1 O-O and suddenly my king is loose. Nd2 looks tempting to... | [
"a6c8"
] |
y6bM7 | 423 | beginner | 5r1k/ppp2rpp/4R1n1/3Q2B1/8/2N5/PP4PP/5R1K b - - 0 22 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king is safe on h8; White's king is on h1 with pawns guarding g2 and h2. I have doubled rooks on the open f-file facing his rook on f1, plus a knight on g6, while White has an active queen on d5, rook on e6, bishop on g5 and knight on c3. First I consider Ne5, but it loses after Rxf7 Nxf7 Re1 as I drop material with... | [
"f7f1"
] |
DUZp1 | 738 | beginner | 8/8/4p3/4Pp2/3PbPp1/pk4P1/1B6/K7 b - - 2 47 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is trapped on a1 with his bishop on b2 doing more harm than good, my king on b3 is active and well-placed, and my bishop on e4 eyes the long diagonal. Material is even but White has no coordination. I first consider capturing the bishop with my king on b2, but that square is attacked by the white king so t... | [
"a3b2"
] |
tbBgG | 860 | beginner | r4r2/pp1np1kp/3p1p2/2pP1Qq1/2P3P1/1P5P/P3PP2/2R1KB1R b K - 0 20 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My queen on g5 is under attack from the white queen on f5 and white's king on e1 looks exposed on the back rank behind the Rc1. First I consider the greedy capture Qxf5, but after gxf5 white has traded queens and my attack disappears. Next I look at advancing with e5, but Rc3 then hits my queen and white continues with... | [
"g5c1"
] |
S9y5C | 741 | beginner | 6k1/1b1r1p2/5Qp1/1p3pN1/2p5/7R/rPP3RP/7K b - - 0 32 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is trapped on h1 by its own Ph2 and Rg2, with my Bb7 pinning the rook down the b7-g2-h1 diagonal and the first rank open. This sets up a back-rank mate with my Ra2.
First I consider the flashy capture Bxg2+. It checks but after Kxg2 the pin is broken, I've traded my strong bishop for a mere rook, and the ... | [
"a2a1"
] |
ei2lp | 962 | beginner | r2qkb1r/pp1nppp1/2p4p/5b2/4N3/3P4/PPP1QPPP/R1B1KB1R w KQkq - 3 9 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king is on e8 boxed in by its queen on d8, knight on d7, pawn on e7, bishop on f8, and pawn on f7, with all adjacent squares occupied and no flight possible. Material is even but my knight on e4 is active and the e-file looks promising once cleared. I first considered Nf6+ as a forcing check but g7xf6 captures ... | [
"e4d6"
] |
xaLWe | 813 | beginner | 7Q/p7/P7/6p1/6p1/1ppk2P1/3p4/3K4 b - - 0 57 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king on d3 is supported by pawns on b3, c3 and d2, with white's king cramped on d1 behind my d2-pawn that already controls c1 and e1. The white queen on h8 is too far to interfere in one move. I should look at forcing options first.
Pushing b3-b2 is tempting to tie white down but it is not check, so the queen comes... | [
"c3c2"
] |
bXHH8 | 861 | beginner | 4r1k1/pp3ppp/8/4Bq2/8/5P1b/PP1R3P/6QK w - - 3 33 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is shut in by its own pawns on f7, g7, h7, and my bishop on e5 is already aimed straight at g7 down the long diagonal. With a queen on g1 sitting on the open g-file (g2 through g6 are all empty), the picture is screaming for Qxg7. Before grabbing it, let me see if anything quieter works. Qg3, Qe3, Qf... | [
"g1g7"
] |
TDQAG | 871 | beginner | 2r2rkb/pp3p2/2pp3P/4p3/4PnN1/3P1P2/PPP5/1K4RR w - - 3 24 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black king on g8 is boxed in by its own Bh8, Rf8 and Pf7 with no pawns on g7/h7; my Ph6 already covers g7 while my Ng4 blocks the open g-file for my Rg1 aimed at the king, with g2-g7 fully clear.
I first looked at h7+ as it drives straight at the king, but after Kg7 the king simply steps aside and I have no follow-up ... | [
"g4f6"
] |
n5KB7 | 618 | beginner | 6k1/pp4bp/2p3p1/4p3/2PPR3/1P4pP/P5P1/2q2Q1K b - - 0 27 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: my king safe on g8, white king on h1, my queen on c1 with clear path along the open first rank to white's queen on f1 (d1 and e1 empty). My g3-pawn cramps white's king while the e4-rook looks active but doesn't defend the back rank. Tempted first by Qc2, which eyes the e4-rook along the diagonal, bu... | [
"c1f1"
] |
u99st | 666 | beginner | r4kr1/2q1bP1p/p2p4/8/3nP3/1BP5/P1P3PP/R4RK1 w - - 0 19 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king is on f8, hemmed in by its own bishop on e7 and rook on g8, while my pawn has reached f7. I notice my bishop on b3 aims down the diagonal toward g8, which will be open after my pawn captures there. The knight on d4 looks tempting but I must focus on the mate. I first consider cxd4 to snatch the knight. How... | [
"f7g8q"
] |
sW8Ph | 932 | beginner | 1r4k1/P5p1/6P1/5P2/5K2/7p/8/8 w - - 0 58 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Looking at the board: my pawn on a7 is one step from promoting, and Black's rook on b8 sits right next to it. The black king on g8 is boxed in by its own pawn on g7, and my pawn on g6 controls both f7 and h7. That king has essentially no air already — so a promotion with check on b8 should be devastating.
axb8=Q is th... | [
"a7b8q"
] |
2efAq | 545 | beginner | 6Q1/8/8/8/8/3kp3/3p4/3K4 b - - 0 56 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king sits on d1 with my king on d3 and pawns on d2 plus e3 cramping it tightly; the white queen on g8 is too far to help immediately. I consider Kd4 first but it lets the queen activate via Qg1+ and then chase my king while I lack material to survive the checks. Ke4 is similar, allowing Qc4+ followed by Qd3 wit... | [
"e3e2"
] |
sqnLl | 744 | beginner | 4k2r/pp3ppp/4p1n1/1q1pP3/1P1n4/P4P2/1R1N2PP/1NQ1K2R b Kk - 0 18 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king on e1 looks exposed on a cluttered back rank with his own Nd2, Qc1, and Rh1 getting in the way. My Nd4 already eyes e2 and supports my Qb5, which has a clear diagonal through c4 and d3 straight to e2. That makes Qe2 the move that jumps out at me.
I first look at the greedy Nxe5, but White answers with Qc8+... | [
"b5e2"
] |
MMqZY | 977 | beginner | 6k1/p1p1rppp/8/2b5/B7/2NP4/PP3RPP/n1B3K1 b - - 0 21 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: white king on g1 has limited squares, with Rf2 pinned to it by my Bc5 along the clear c5-d4-e3-f2-g1 diagonal, while my Re7 has fully open e-file down to e1. Material is even but the pin and file point to a back-rank idea. First I consider the tempting Nb3 with my knight from a1, attacking the Ba4, ... | [
"e7e1"
] |
YSiTm | 951 | beginner | r1b2nkr/pp4pp/2p5/q1b1N1B1/3P4/8/P1P3PP/R4QK1 w - - 0 16 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: my king safe on g1, active Ne5 and Bg5, Qf1 on open file, while black's Kg8 is cramped by its Nf8, Rh8, and pawns on g7/h7; black's Qa5 is out but not threatening me. The f7 weakness covered by my knight is the key motif.
A tempting try is Qxf8+, taking the knight with check, but the king safely rec... | [
"f1f7"
] |
og3Us | 937 | beginner | r4rk1/5p1p/p4Qq1/1p2B3/8/7P/6PK/8 w - - 1 28 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is safe on h2 while Black's king on g8 is boxed in by its own rook on f8 plus pawns on f7 and h7. My queen on f6 and bishop on e5 eye the kingside, with the bishop on the e5-f6-g7-h8 diagonal now blocked by my queen. I first considered the greedy Qxg6 capturing Black's queen with check, but the pawn on f7 ... | [
"f6h8"
] |
vwOWw | 555 | beginner | r1b1r1k1/1p3ppp/pp3q2/8/PP3p2/2PP1B2/5PPP/R2QR1K1 w - - 2 19 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: my king is safe on g1 while black's king on g8 is boxed in by his pawns on f7, g7, and h7. Black's e8 rook sits on an open file opposite my e1 rook, with the back rank further weakened by the c8 bishop and a8 rook. Material is balanced but the alignment screams for attention.
First I consider the qu... | [
"e1e8"
] |
OphlM | 834 | beginner | r2qrk2/1p3ppQ/5b2/p2p3P/2p5/3B1P2/PPPK4/4R2R w - - 0 24 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on f8 is hemmed in by its own Re8, Pf7 and Pg7. My Qh7 is deep in enemy territory with Re1 lining up on the e-file. Rxe8+ is tempting but after Kxe8 the king slips to d7 and I have no mate. Bf5 looks aggressive yet Black replies g6 and holds after hxg6 Qc7. Bg6 runs into Re6 and Black equalizes after Rxe6 ... | [
"h7h8"
] |
ceXJ4 | 857 | beginner | 6k1/p4rpp/2R5/3B4/3p1P2/3n2P1/Pr5P/6K1 w - - 0 25 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king is hemmed in on g8 by its pawns on g7 and h7 plus the rook on f7. My rook on c6 has a clear path to the empty back rank while my bishop on d5 lines up on the diagonal toward g8 once f7 clears. Black's rook on b2 and knight on d3 are active but do not defend the king.
I first consider Rc7. It eyes the f7-ro... | [
"c6c8"
] |
uM9US | 777 | beginner | r1b2rk1/5ppp/2p5/p1bP4/6n1/PP4P1/1B1NP1BP/R2Q2RK b - - 0 17 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king on h1 is jammed against its own crew: rook on g1, bishop on g2, pawn on h2 — no luft at all. My knight on g4 and bishop on c5 are already pointing at that corner; the bishop rakes the a7-g1 diagonal through d4-e3-f2-g1. That screams Nf2. Let me check it properly. Nf2 hits h1 with the knight, so it's check.... | [
"g4f2"
] |
dg6R3 | 479 | beginner | 5r2/ppp1N1pk/6p1/8/8/4R3/2q2rP1/4R1K1 w - - 0 29 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king sits on h7 restricted by his own pawns on g6 and g7. My Ne7 controls g8, I have rooks on e1 and e3 plus a pawn on g2, while Black threatens with the queen on c2 and rook on f2. I first look at Kh1 to step out of any lines, but Black answers Rf1+ Kh2 R1f5 and I am losing. Next I try R3e2 to challenge the qu... | [
"e3h3"
] |
ZJ8Tz | 740 | beginner | 3qrbk1/3b2p1/2p1prQ1/1pP3N1/1B1P1P2/P2R4/8/2K3R1 w - - 9 37 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is boxed in by its own pieces — bishop on f8, pawn on g7 — and my queen on g6 with the knight on g5 are sitting right next to it. That's the kind of cluster that usually has a mate. The greedy capture Qxf6, grabbing the rook, just loses to Qxf6 since nothing of mine defends f6. Qxe8 similarly drops t... | [
"g6h7"
] |
nf8bt | 874 | beginner | 3R2bk/p5br/1p6/1Pp1q1N1/P1P2pP1/2n4P/6BK/8 w - - 0 40 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on h8 is suffocating — g8 has his own bishop, g7 his own bishop, h7 his own rook. And my rook on d8 already eyes the 8th rank, with only the bishop on g8 in between, so that bishop is pinned to the king. That pin is the key to the whole position. Rxg8+ looks flashy but it's wrong: after Kxg8 the king escap... | [
"g5f7"
] |
eeVpR | 727 | beginner | 6k1/pp4pp/4b3/3p2Q1/3q4/8/P1r2RPP/R5K1 w - - 2 23 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is hemmed in by its pawns on g7 and h7 with an empty back rank while my queen on g5 and rook on f2 are active. I first consider Qf4 but it loses to Qxa1+ Rf1 Qf6 and Black wins material. Qg3 runs into Rxf2 Re1 Re2+ with strong counterplay. Rb1 allows Qxf2+ Kh1 h6 and I am losing. Instead Qd8 checks a... | [
"g5d8"
] |
vFhE1 | 628 | beginner | q5k1/p2n1ppp/6r1/4pb2/7Q/2N1P3/PP3PPP/R4R1K b - - 6 18 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king is safe on g8 and the white king on h1 is jammed in the corner with its own pawns on g2 and h2 right next to it — that's the kind of structure where a back-rank or corner mate often appears. Let me look at my heavy pieces. The queen on a8 stares straight down the long diagonal a8–h1, and crucially the squares b... | [
"a8g2"
] |
E5qMJ | 736 | beginner | 4r1kr/p1b2q1p/4RB2/2P3p1/2Q5/8/PP3PPP/2K5 w - - 1 26 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is boxed in by its queen on f7, pawn on h7, and rook on h8. My rook on e6 lines up on the e-file against the enemy rook on e8, my bishop on f6 eyes g7, and my queen on c4 aims along the diagonal through f7 toward g8.
I first consider Bxh8 to grab the rook. Black replies Rxe6 and is up material afte... | [
"e6e8"
] |
9SmT0 | 607 | beginner | 6k1/1p3pbp/1pp3p1/8/2P5/1PN4P/P4PP1/6K1 b - - 0 27 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king sits on g1 with no immediate threats, my king is safe on g8, and material is even except white's knight on c3 looks vulnerable. My bishop on g7 has a clear path down the long diagonal through empty f6, e5, and d4. First I check if the knight is defended: the b3 pawn only controls a4 and c4, the c4 pawn hit... | [
"g7c3"
] |
piRq0 | 962 | beginner | r1b2rk1/p1q2pBp/2p2b2/2pppP2/4P1Q1/2NP4/PPP3PP/R4RK1 b - - 0 14 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Let me look at what's happening on the kingside. White's bishop has landed on g7, right next to my king on g8 and attacking my bishop on f6. That bishop on g7 is itself attacked twice — by my Bf6 and by my king on g8 — and defended once, by the white queen on g4 looking straight up the g-file (g5 and g6 are empty). So ... | [
"f6g7"
] |
Ed5wn | 741 | beginner | r1bqkb1r/pp2pppp/3p4/1N1PP3/Q4Pn1/2P5/6PP/n1B1KBNR w Kkq - 0 14 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | The black king on e8 is restricted by its queen on d8, bishop on f8, and pawns on e7 and f7, leaving only d7 as a potential flight square. My queen on a4 aims directly at the king along the a4-b5-c6-d7-e8 diagonal, masked only by my knight on b5. Moving the knight will discover check from the queen.
I first consider e6... | [
"b5c7"
] |
90QiS | 598 | beginner | r2q1r1k/ppp3pn/2np2bp/2bB4/5N2/2N3PP/PP1P3K/R1B2R2 w - - 0 15 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on h8 is trapped by his own Nh7, Pg7, and Ph6 while my Bd5 covers the g8 flight square down the open d5-e6-f7-g8 diagonal. A safe check should end the game. I first consider b4 to hit the Bc5, but it allows Rxf4 Rxf4 Nf6 and I lose material with no compensation. Next I look at d4, yet Black again takes Rxf... | [
"f4g6"
] |
ZPY3J | 905 | beginner | 4r1k1/1b3r1p/1n3qpQ/1pp2p2/p7/P2P1P1P/BPP3P1/4RRK1 w - - 0 25 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king is on g8 with my queen on h6 already eyeing g7. I have an open e-file to the black rook on e8 and my bishop on a2 pins the rook on f7 straight through to the king on g8 along the empty a2-b3-c4-d5-e6-f7-g8 diagonal. Bxf7+ looks tempting to smash the kingside but after Qxf7 my attack ends and the position i... | [
"e1e8"
] |
xKIFb | 411 | beginner | r5k1/2R2ppp/1pN1p3/1Ppp4/5P2/1PP5/5PPP/6K1 b - - 0 25 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is trapped on g1 by its own pawns on f2, g2 and h2 while my rook on a8 has a completely open a-file and the entire first rank up to f1 is empty. Ra1# looks strong. I first considered the quiet c4 but after Rc8+ I must play Rxc8 and after bxc4 the game continues even if I am up material. I also looked at d4... | [
"a8a1"
] |
1lz9l | 808 | beginner | 3R4/r4kp1/2pBp2p/1bP4P/8/p4P2/6P1/6K1 w - - 0 38 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on f7 is restricted by its own pawns on e6 and g7 while my Bd6 already covers e7. I first consider Kf2 to improve my king but Black replies g6 and after Rh8 Kf6 the king slips out with a roughly equal position. Next I look at g4 hoping to open lines but it allows e5 and even Rf8+ then lets the king escape ... | [
"d8f8"
] |
K2fWa | 775 | beginner | b1k5/8/8/pp3P2/8/PP6/6PP/4rR1K b - - 2 43 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My rook on e1 eyes the open back rank with White's king trapped on h1 by its own pawns on g2 and h2. White's rook on f1 is the only defender there while my king and bishop sit safely on the queenside. Re2 looks tempting at first as it slides deeper and eyes the g2 pawn, but Rg1 Kd7 h4 lets White defend and the game con... | [
"e1f1"
] |
oBcnJ | 915 | beginner | 5k2/pp3pq1/2p2Q2/3p4/7P/PB6/KP6/2b5 w - - 1 52 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king is on f8, hemmed in by its own queen on g7 and pawn on f7. My queen on f6 sits right next to the king, and the back rank is completely empty. That smells like a back-rank finish. Qxg7+ is the obvious grab but nothing of mine defends g7, so Kxg7 just wins the queen. Qd6+ gives check but Kg8 escapes and ther... | [
"f6d8"
] |
pgp9l | 815 | beginner | rn1q1rk1/p1b2ppp/4p3/1p2P1N1/2pP4/2P3P1/2Q2PbP/R1B2RK1 w - - 0 15 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My knight on g5 and queen on c2 both eye the black kingside while the loose bishop on g2 sits next to my king on g1. First I consider Kxg2 to grab the bishop, but then Black plays Qd5+ and after f3 g6 my king is exposed with no quick mate. Next I look at f4 hoping to open the position, yet Black replies Qxg5 and after ... | [
"c2h7"
] |
oFTLZ | 750 | beginner | 6Q1/5Q2/pk2p3/1ppb4/2qP4/P1P5/1P6/K7 b - - 0 39 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is trapped on a1 by its own pawns on a3 and b2, while my queen on c4 and bishop on d5 control the long diagonal. I need to find a forcing check that finishes the game. Qf1+ looks tempting as it attacks down the first rank with a clear path, but after Qxf1 I lose the initiative and white's queens coordinate... | [
"c4a2"
] |
bNNez | 693 | beginner | r2qkb1r/1bp2npp/p2p1n2/1p2p1NQ/4P3/P2P4/1PP2PPP/RNB1K2R w KQkq - 0 10 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My queen on h5 attacks along the diagonal toward the black king on e8, blocked only by the knight on f7. That knight is also attacked by my knight on g5, and defended solely by the king on e8; the bishop on f8 cannot reach f7, nor can the queen on d8 or knight on f6. First I consider Nxf7, but black replies Nxh5 and wi... | [
"h5f7"
] |
Fus08 | 772 | beginner | r1b2rk1/pp6/3p2pQ/2p1p3/2PnP3/2NP2P1/PP3q1P/2KR1B1R b - - 0 16 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White king on c1 is exposed, my queen already on f2 and knight on d4 both eye the area around it, while my king on g8 is safe for now. White's queen on h6 threatens g6 but I can ignore if I find mate. Material is even.
I should weigh some tempting moves before committing. Bh3 develops my light bishop with tempo but af... | [
"f2c2"
] |
9uuUN | 757 | beginner | 2b4r/p4q1k/6pp/6p1/3QP3/2B4P/PP4P1/6K1 w - - 0 46 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I start by surveying the board: my king safe on g1, black's king exposed on h7 with its own pawns on g6 and h6 restricting it, black's rook on h8 and queen on f7. My queen on d4 and bishop on c3 line up on the long diagonal toward h8 with e5 f6 g7 empty.
Tempting first is Qg7 check along that diagonal. It checks the ki... | [
"d4h8"
] |
YYxwS | 709 | beginner | 2r4k/p4p1p/1p2p2Q/3pq3/8/2P5/PP6/K6R w - - 0 30 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: black king on h8 is restricted by his own pawns on f7 and h7 with g7 empty, my Qh6 stands right next to him, and my Rh1 lines up on the open h-file once the queen shifts. Black's Qe5 and Rc8 are active but distant, my Ka1 is safe, and material is even enough that a direct mate wins.
One tempting tr... | [
"h6h7"
] |
q5bTb | 930 | beginner | r5k1/1pQn1ppp/1p6/1P6/2P5/P2qBP2/3R1P1P/7K b - - 1 27 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is on h1, hemmed in by its own pawns on f2 and h2 with an open first rank. My queen on d3 eyes back-rank chances while White's queen on c7 threatens my knight on d7. Qb1+ looks natural but after Kh1-g2 the king escapes and I have no strong follow-up. Qf5, Qg6, and Qc3 are quiet but all allow Qc7xd7, losing... | [
"d3f1"
] |
CHPIy | 923 | beginner | 2k5/1p1n1p2/8/1p1p1B2/8/P3bPB1/2p1rNK1/7R w - - 3 33 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on c8 is restricted by its own Pb7 and Nd7. My Rh1 has a clear path to h8, so I try that first. Bxc2 seems tempting to grab the pawn but after Kd8 I play Rh8+ Ke7 and the game continues without forced mate. Bd3 looks active but allows Rxf2+ Bxf2 c1=Q with Black promoting. Those are inferior. So Rh8 checks ... | [
"h1h8"
] |
6EUQC | 699 | beginner | 2b2r1k/2rq2p1/4p1Qp/4P3/3P1R2/5P2/P5PP/3R3K w - - 4 36 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on h8 is hemmed in by pawns on g7 and h6 with my Qg6 already covering the h7 flight square. The Rf8 is undefended: Bc8 cannot guard it horizontally, Qd7 has no path to it, Rc7 misses it, and Kh8 is too far away.
I first consider Qh7+ as a checking try, but it fails because nothing protects h7 so the king ... | [
"f4f8"
] |
jPJYi | 436 | beginner | 2k5/2Pr4/1PK5/8/8/8/8/6q1 w - - 0 67 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black king is on c8 right next to my king on c6, with my c7 pawn controlling b8 and d8 while my b6 pawn is poised to advance. Black's rook on d7 and queen on g1 are not checking me. I first consider Kb5 but Black replies Rd5+ forcing my king to b4 where Qd4+ leads to quick mate against me. Next I look at Kd5 which fail... | [
"b6b7"
] |
cr5FL | 506 | beginner | 8/6P1/7p/1p2P2P/1p3P2/1Ppk4/P2p4/3K4 b - - 0 52 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king on d3 with the d2-c3 pawn chain cramps White's king on d1, and the g7 pawn is one move from promoting so I must find something forcing. First I consider Kd4 but then g8=Q Kc5 Qe6 wins for White; Ke4 runs into the same with g8=Q Kf3 Qg6 and I lose. Trying to push the d2 pawn fails because d1 is occupied by his k... | [
"c3c2"
] |
joOsg | 835 | beginner | r3kb1r/1pp2p1q/p4p2/4p3/3nP1Q1/2NP2pB/PP3P1P/R4RK1 w kq - 2 17 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on e8 is still in the centre, walled in by its own rook on a8, bishop on f8, rook on h8 and pawns on b7, c7, f7 — so escape squares are scarce. My queen on g4 and bishop on h3 share the b1–h7... no, the h3–c8 diagonal, and that diagonal runs straight through d7 to the king's neighbourhood. That's the hook.... | [
"g4d7"
] |
rSEUu | 852 | beginner | 8/1r6/p2PB3/2R5/5p1p/3bp1k1/6P1/6K1 w - - 4 57 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king stands exposed on g3 with scant protection while my king on g1 and g2-pawn control the nearby light squares. I have an active Rc5 and Be6 plus the d6-pawn; this suggests hunting checks or a direct mate. First I consider the quiet Rc1 aiming to activate but it is too slow: Black plays ...f3, I capture gxf3,... | [
"c5g5"
] |
HQG04 | 904 | beginner | r1b1k2r/pppp1ppp/2n5/8/4P1nq/3P1N2/PPP1K1PP/RNBQ1B1R b kq - 4 8 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is exposed on e2 with weak pawn cover while my queen on h4 and knight on g4 are aimed at that sector; the knight on g4 controlling f2 and e3 is the key motif. I first look at Nd4+ with the c6-knight as a forcing check, but after Kd2 my Qf2+ lets the king slip away via c3 with no mate. Next I consider Qh5 h... | [
"h4f2"
] |
EI9QN | 399 | beginner | 5rk1/3nqppb/2rb3p/pp6/4p1Q1/PP2P2P/1BPN1PP1/R3K2R w KQ - 0 19 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is cramped by its own pieces on f7, g7, h7 and f8. My Qg4 aims at g7 while Bb2 controls the open long diagonal (c3, d4, e5, f6 all empty) so it backs up any capture on g7. That looks like mate, but I should check alternatives first. Nc4 looks active but after Nf6 the knight hits my queen on g4; if I ... | [
"g4g7"
] |
aXd4N | 960 | beginner | 2b1n1k1/1p2Qp1p/5np1/1p1p4/1B6/5P2/6PP/q4NK1 w - - 0 33 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is on g1 with three pawns shielding it while Black's king on g8 is restricted by his own pawns on f7, g6, and h7. My queen on e7 and bishop on b4 both eye the dark squares around the king, with the b4-c5-d6-e7-f8 diagonal ready to open. I first look at Bc5 to line up on that diagonal, but after Bc5 h5 my l... | [
"e7f8"
] |
8jpjV | 483 | beginner | r3kb1Q/pp2q2p/6p1/3p4/8/8/PP3PPP/RNB3K1 b q - 0 18 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king sits on g1 with Ra1, Nb1, and dark-squared Bc1 on the first rank while f1 and h1 remain uncovered. My Qe7 has a fully open e-file down to e1. I could try O-O-O first, but that runs into Qc3+ Kb8 Bf4+ and White's pieces swarm my king. Kf7 is another way to step out, yet it allows Be3 followed by Rd8 or Qc3 ... | [
"e7e1"
] |
gWftl | 693 | beginner | 8/p1R5/P7/1k2P3/8/8/3p1PPP/5K2 b - - 0 37 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My pawn on d2 is one step from promotion, and White's king sits on f1 right on the first rank. That's the whole game — if I promote on d1 with check, can White wriggle out?
d1=Q+ puts the new queen on d1, checking along the first rank to f1 with e1 empty. Let me walk the king's escape squares: e1 is next to the queen ... | [
"d2d1q"
] |
Ytaa1 | 909 | beginner | 5r1k/1p4pp/p1n3r1/2Q2p2/3P4/P1P4R/1q4PP/5RK1 w - - 0 28 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on h8 is trapped by its own pawns on g7 and h7. My queen on c5 has a clear diagonal to the undefended black rook on f8. I first consider Rh8 but the path is blocked by the h7 pawn so the move is illegal. I next look at Rf2 but black replies Qb1+ Rf1 Rxg2+ and I do not force mate. Qxf8+ is better: it captur... | [
"c5f8"
] |
uBWtc | 730 | beginner | r3k2r/1ppb1p1n/p2p1q1p/P5p1/1PP1PpP1/3P1P1P/3Q3N/R3KB1R b KQkq - 1 21 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king sits safely on e8 while white's king on e1 looks exposed along the back rank with pieces cluttered nearby. Material is equal but the open a1-h8 diagonal catches my eye: from my queen on f6 the path e5-d4-c3-b2 is fully clear to white's undefended rook on a1.
First I weigh some tempting alternatives. Nf8 devel... | [
"f6a1"
] |
ZHUBu | 963 | beginner | 2b3k1/5pp1/p6p/2r5/PQP1B3/2P5/4p1PP/5R1K b - - 0 38 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king sits on h1 shielded by pawns on g2 and h2, with the queen on b4, rook on f1, and bishop on e4. I have a safe king on g8, a rook on c5, bishop on c8, and a pawn one step from promotion on e2. The e2 pawn capturing the f1 rook is the forcing idea to consider. First I look at the tempting quiet a5 attacking t... | [
"e2f1q"
] |
3PqGV | 853 | beginner | r4k1r/ppp2Pp1/8/3P3p/5B1N/P1N4n/1P4PP/6RK b - - 0 26 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king is trapped on h1 with its own rook on g1 and pawns on g2 and h2 covering all escape squares. My knight on h3 is perfectly placed to exploit this. Nxf4 looks tempting as it takes the bishop with no immediate recapture, but after Rf1 White activates the rook on the f-file and supports the pawn on f7 for dang... | [
"h3f2"
] |
b1Wci | 965 | beginner | 6k1/1b2qR2/1p4p1/2p4p/P1Bb4/1P2r3/2P3PP/1R1Q2K1 b - - 0 27 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king on g8 is safe but White's king on g1 looks vulnerable on the back rank, with my Re3, Bd4, Qe7, and Bb7 all aimed there. White's Rf7 is hanging but I first check Qxf7; that allows Bxf7+ Kxf7 when my king is too exposed and White slips away to h1, no quick mate. Next I look at Qe5 to centralize and attack; White ... | [
"e3e1"
] |
W8Vs6 | 861 | beginner | 8/1R6/1p4P1/7K/5k2/8/8/1r6 b - - 0 53 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king on f4 controls g5 g4 g3 f5 e5 e4 e3 while the white king is exposed on h5 with only the g6-pawn and distant b7-rook for support. The first rank is open for my b1-rook and the h-file is clear. I could try Kf5 but white answers Kh6 and after my Kf6 the rook comes to f7 with check allowing counterplay. Or b5 advan... | [
"b1h1"
] |
pPh3Q | 592 | beginner | 3q2k1/5p1p/5QpP/p7/1p6/8/5PP1/6K1 w - - 0 38 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is cramped by its own pawns on f7, g6, h7 while my h6-pawn controls g7 and my queen sits on f6 ready to strike. I need a forcing kill.
First I look at Qxf7+. My queen captures the pawn and checks the king from f7, but the king just takes it safely on f7 since nothing defends that square (my h6-pawn o... | [
"f6d8"
] |
x6oTf | 974 | beginner | r4rk1/1p2bppp/4q3/3p1N2/p1p5/2Pn2Q1/PP1P2PP/R1B2R1K w - - 8 22 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king on g8 is boxed in by its own pawns on f7, g7, h7 and the rook on f8, and my knight on f5 already eyes g7 and h6. With the queen on g3 lined up on the g-file, Qxg7 looks like the immediate finish — let me check the alternatives first to be sure. Nxg7 grabs the pawn with the knight but it isn't even check (t... | [
"g3g7"
] |
hBHo2 | 630 | beginner | 5k2/3P1ppp/8/4p1P1/P6P/3p2P1/1p6/6K1 w - - 0 36 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My d7-pawn is one step from promotion while Black's b2-pawn threatens to queen next. Black's king on f8 is hemmed in by its pawns on f7, g7 and h7, and my g5-pawn cuts off f6. I must act now. First I look at Kg2 to stop the b-pawn, but Black answers Ke7 and next takes b1=Q while my d7-pawn sits idle. Kf2 runs into the ... | [
"d7d8q"
] |
fbU12 | 885 | beginner | 3k2r1/2pr1p2/p1p3qp/P3P3/3P4/Q3n3/1R4PP/6K1 w - - 0 34 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the board: Black's king on d8 is restricted by its own rook on d7, pawn on c7, and rook on g8. The knight on e3 is undefended. My rook on b2 has a clear path up the open b-file, and my queen on a3 controls the diagonal toward e7. A back-rank mate seems possible, but I must check alternatives.
Grabbing the kni... | [
"b2b8"
] |
ghQZf | 915 | beginner | r4rk1/ppp2pp1/3pb2p/3N1P2/1PBBP1n1/P2P2q1/2P3P1/R2Q1RK1 b - - 0 16 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I see my queen on g3 and knight on g4 hovering near the white king on g1, which is cramped by its own rook on f1 and pawn on g2. This screams mate in one. First I check the obvious aggressive tries. Qxg2+ looks flashy as a check, but the king captures safely on g2 since my knight does not defend that square and I lose ... | [
"g3h2"
] |
hnaii | 412 | beginner | 6k1/5p1p/p5p1/2p5/Np1b3B/8/PPP2PPP/3rR1K1 b - - 2 25 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king on g1 is boxed in by its own pawns on f2 g2 h2 with the rook on e1 next to my rook on d1. Rxe1 jumps out as a capture that might end it. Before taking I check tempting alternatives. Bxf2+ with my bishop on d4 checks but white's bishop on h4 recaptures and I simply trade down into a balanced endgame. Rd2 lo... | [
"d1e1"
] |
iD23Z | 498 | beginner | 6k1/5pp1/p3p2p/1p6/2r1BP2/PbP4P/1P1R2P1/6K1 w - - 1 32 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My king sits safely on g1. Black's king on g8 is hemmed in by its own pawns on f7 and g7. My bishop on e4 has a clear diagonal to cover h7, and my rook on d2 sees all the way up the open d-file.
I first consider Bb7, but Black replies a5 and after Rd8+ the king slips out to h7 safely now that my bishop has left e4. Bb1... | [
"d2d8"
] |
tRQYX | 817 | beginner | r4rk1/pp1qbppp/1np1p3/8/8/1QPB4/PP3PPP/RNB2RK1 b - - 0 13 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I see the white bishop sitting on d3 with no defenders: the queen on b3 is blocked by its own pawn on c3, the knight on b1 cannot reach d3, the dark-squared bishop on c1 is on the wrong color, and no pawns or rooks cover it. My queen on d7 has a completely open path down the empty d-file to capture it. Qxd3 looks like ... | [
"d7d3"
] |
BwPHS | 438 | beginner | 5rk1/5ppp/p3p3/8/pP6/P4q2/4r1RP/Q6K w - - 0 27 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black is threatening mate himself — the queen on f3 together with the rook on e2 means ...Qxg2# wins on the spot, since the queen lands defended by the rook along the 2nd rank and my king on h1 has no flight. So a quiet move like Qg1, Qf1, h3 or b4-b5 just loses. I need to deliver mate this move. Looking at my queen on... | [
"a1g7"
] |
o4Jo2 | 625 | beginner | r1r3k1/1b3p2/3ppbp1/8/1R2P1QP/6N1/PR3PP1/K1B5 b - - 0 33 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king sits on a1 shielded only by the bishop on c1 along the back rank, with my rook on c8 staring down the fully open c-file and my bishop on f6 aiming through the rook on b2. Rxc1 is the obvious capture to try. It seizes the bishop, checks the king along the first rank, and lands on a square nothing defends: t... | [
"c8c1"
] |
CD3Oo | 541 | beginner | r1bq1rk1/1pp1bppp/p2p4/3n4/2PQ4/1P2P3/PB3PPP/R3KB1R w KQ - 0 11 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king sits on g8 hemmed in by his own pawns on f7 g7 h7 plus the rook on f8. My Qd4 and Bb2 line up on the long diagonal with c3 e5 f6 empty so the bishop aims straight at g7. I first consider cxd5 but Black replies Bf6 attacking my queen on d4 forcing me to retreat while he follows with Bd7 and the game stays e... | [
"d4g7"
] |
hKTD6 | 710 | beginner | 3r1k1r/pp2ppbp/2p3pB/2q5/8/2N5/P1P2PPP/3RR1K1 w - - 0 19 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | Black's king sits on f8 with the rook on d8 right in front of it, and my rook on d1 is already staring down the open d-file — d2 through d7 are all empty. That immediately suggests Rxd8+. Before I jump on it, let me see what else might tempt me. Be3 or Bf4 just retreats the bishop and lets Black play Rxd1 first, untang... | [
"d1d8"
] |
SU4sU | 643 | beginner | 8/5ppk/4p2p/1Q1pP3/5P2/7P/p1rr4/R5RK b - - 0 37 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | My Rc2 and Rd2 are doubled on the second rank staring at White's cramped king on h1, backed only by his Rg1 and Ph3. Black is down material but can force mate. Rb2 looks tempting to keep pressure but after Qxb2 Rxb2 White plays Rac1 and equalizes with active pieces. d4 fails to a strong reply like Rg3 attacking my rook... | [
"d2h2"
] |
9Em96 | 693 | beginner | 6k1/1q5p/p3p3/1p6/8/1P2Bp2/2P4P/4RR1K b - - 0 36 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | I survey the key features: white king on h1 is vulnerable on the long diagonal from my queen on b7, currently screened by my pawn on f3 which can move forward. White has a bishop on e3 that might defend, rooks on the first rank, and pawns on b3, c2, h2. No immediate material to grab.
Tempted to first play a5, but this... | [
"f3f2"
] |
sJxQh | 813 | beginner | 5r1k/4b2p/p3B3/1p2Pp2/4P1p1/P1q1QbP1/2PN3P/2R1KR2 b - - 0 30 | [
{
"role": "system",
"content": "You are a chess engine. Given a position, find the single best move for the side to move — every puzzle has exactly one winning move.\nBoard: uppercase=white, lowercase=black, '.'=empty.\nReason inside <think>...</think>. After </think>, output exactly one move in SAN (standa... | White's king sits exposed on e1 while my queen on c3 directly eyes the undefended queen on e3 with d3 empty. I have a material edge with two active bishops and an advanced g4-pawn, while White's back rank looks vulnerable with the king boxed in. I first examine the greedy Qxe5 capturing a pawn, but Nxf3 forces gxf3 and... | [
"c3e3"
] |
End of preview. Expand in Data Studio
Chess Puzzle Chain-of-Thought (augmented)
Chain-of-thought traces for one-move Lichess puzzles (beginner bucket, rating 399–999). This is the augmented CoT set used as SFT data for the chess reasoning models, oversampling weak tactical families (hanging pieces, pins, advanced pawns, promotions, discovered/double checks, and scarce advantage/crushing material wins).
Schema
| field | type | description |
|---|---|---|
puzzle_id |
string | Lichess puzzle id |
rating |
int | Lichess puzzle rating (399–999) |
bucket |
string | difficulty bucket (beginner) |
fen |
string | starting FEN (side to move = solver) |
prompt |
list[{role, content}] | chat-format system+user prompt |
completion |
string | CoT in <think>...</think> then the SAN move |
expected_moves |
list[string] | the single winning move (UCI) |
Details
- Rows: 4,823
- Source positions: Lichess one-move puzzles under 1000 elo
- CoT generation: model-generated, then engine/verifier checked against the known winning move
- Disjoint from the RL training split.
- Downloads last month
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