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Chess Position Evaluator (Stockfish via x402)
x402
Chess Position Evaluator (Stockfish via x402) is a paid API for AI agents from chess-eval.x402supply.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-30).
Evaluates a chess position using real Stockfish 10 (asm.js), returning the best move, centipawn/mate score, and principal variation for a given FEN string.
Price / call$0.01
Success—
StatusUnknown
How this service works
Evaluate a chess position with Stockfish: best move, centipawn/mate score, principal variation, and optional multipv. No mocks — a real single-threaded Stockfish 10 (asm.js) runs in-isolate per call.
Output
Returns the best move in UCI notation, a centipawn score (or mate-in-N score), and the principal variation sequence. If multipv is set (1–5), returns multiple ranked candidate moves with individual scores and variations.
Example use cases
Best move for critical game position
“I'm in a tough spot in my chess game — the FEN is r1bqk2r/ppp2ppp/2np1n2/2b1p3/2B1P3/2NP1N2/PPP2PPP/R1BQK2R w KQkq - 4 6. Can you run Stockfish at depth 16 and tell me the best move and the score?”
Opening theory verification
“Can you check if e4 e5 Nf3 Nc6 Bb5 is the best line? Run a depth-12 Stockfish eval on rnbqkb1r/pppp1ppp/5n2/1B2p3/4P3/5N2/PPPP1PPP/RNBQK2R b KQkq - 3 3 and give me the top 3 candidate moves with their scores.”
Endgame accuracy check
“I want to know if I'm playing the endgame optimally — FEN is 8/8/4k3/8/4K3/8/4P3/8 w - - 0 1. Evaluate it with Stockfish at depth 18 and tell me the best move and whether there's a forced mate.”
Technical details
Endpoint
POSThttps://chess-eval.x402supply.com/tools/evaluate_position?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need a real, deterministic Stockfish engine evaluation (not a mock or heuristic) for a single chess position given as FEN. It is ideal for agents that need authoritative centipawn scores, best-move recommendations, or principal variations without setting up a local engine. Supports up to 5 multipv lines and depth up to 18, making it suitable for both quick blunder checks and deeper positional analysis.
Side effects
- Invalid FEN string — position cannot be parsed, returns error
- Depth out of range (must be 1–18) — returns validation error
- multipv out of range (must be 1–5) — returns validation error
- Timeout or isolate crash if position is extremely complex — may return partial results or error
- Payment failure (x402) — call rejected before evaluation runs
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| fen | string | |
| depth | integer | |
| multipv | integer |
Output
Schema · Response
{
"type": "json",
"example": {
"pv": [
"d5",
"e5",
"d4",
"c3",
"Nc6",
"Nf3",
"dxc3"
],
"pvUci": [
"d7d5",
"e4e5",
"d5d4",
"c2c3",
"b8c6",
"g1f3",
"d4c3"
],
"engine": "stockfish 10 asm.js",
"evalCp": -29,
"status": "ok",
"multipv": [
{
"pv": [
"d5",
"e5",
"d4",
"c3",
"Nc6",
"Nf3",
"dxc3"
],
"move": "d7d5",
"pvUci": [
"d7d5",
"e4e5",
"d5d4",
"c2c3",
"b8c6",
"g1f3",
"d4c3"
],
"evalCp": -29,
"moveSan": "d5"
}
],
"bestMove": "d7d5",
"timedOut": false,
"fenEchoed": "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
"bestMoveSan": "d5",
"perspective": "side-to-move",
"depthReached": 10
}
}Tags
x402
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