x402supply-com Chess Eval API
The chess-eval API from x402supply-com — 3 operation(s) for chess-eval.
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OpenAPI Specification
openapi: 3.2.0
info:
title: Chess Eval API
version: 0.1.0
description: '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.; Play out Stockfish''s predicted principal variation as SAN moves with a per-ply eval, re-searching after each ply.'
x-guidance: 'Call `evaluate_position` with a FEN to get the engine''s best move, centipawn/mate score, principal variation, and (optionally) the top `multipv` distinct lines. Call `best_line` to get the full predicted line as SAN moves with a per-ply eval instead of just the top move. FEN is validated strictly before the engine runs (illegal or malformed FEN is rejected before any Stockfish work). `depth` defaults to 12 (1-18) and is capped by a ~9.5s wall-clock budget per call — a deep request may return early with `depthReached` below the requested depth and `timedOut: true`. Terminal positions (checkmate/stalemate/draw) return that `status` with no move.'
contact:
email: contact@gratefuldevai.com
servers:
- url: https://chess-eval.x402supply.com
tags:
- name: chess-eval
paths:
/mcp:
post:
operationId: chess-eval_call
summary: Call chess-eval via MCP tools/call
tags:
- chess-eval
requestBody:
required: true
content:
application/json:
schema:
oneOf:
- type: object
required:
- jsonrpc
- id
- method
- params
properties:
jsonrpc:
const: '2.0'
id:
type:
- string
- number
method:
const: tools/call
params:
type: object
required:
- name
- arguments
properties:
name:
const: evaluate_position
arguments:
type: object
properties:
fen:
type: string
depth:
type: integer
minimum: 1
maximum: 18
multipv:
type: integer
minimum: 1
maximum: 5
required:
- fen
additionalProperties: false
$schema: http://json-schema.org/draft-07/schema#
- type: object
required:
- jsonrpc
- id
- method
- params
properties:
jsonrpc:
const: '2.0'
id:
type:
- string
- number
method:
const: tools/call
params:
type: object
required:
- name
- arguments
properties:
name:
const: best_line
arguments:
type: object
properties:
fen:
type: string
depth:
type: integer
minimum: 1
maximum: 18
maxPlies:
type: integer
minimum: 1
maximum: 40
required:
- fen
additionalProperties: false
$schema: http://json-schema.org/draft-07/schema#
responses:
'200':
description: Tool result
content:
application/json:
schema:
oneOf:
- type: object
description: JSON-RPC 2.0 response envelope. `result.content[0].text` is a JSON-encoded string matching the schema in `x-mcp-result-schema`.
properties:
jsonrpc:
const: '2.0'
id:
type:
- string
- number
result:
type: object
properties:
content:
type: array
items:
type: object
properties:
type:
const: text
text:
type: string
x-mcp-result-schema:
type: object
required:
- status
- bestMove
- pv
- depthReached
- timedOut
- multipv
- engine
- fenEchoed
properties:
status:
type: string
enum:
- ok
- checkmate
- stalemate
- draw
bestMove:
type:
- string
- 'null'
bestMoveSan:
type:
- string
- 'null'
pv:
type: array
items:
type: string
description: Principal variation in SAN
pvUci:
type: array
items:
type: string
depthReached:
type: integer
timedOut:
type: boolean
multipv:
type: array
items:
type: object
required:
- move
- moveSan
- pv
- pvUci
properties:
move:
type: string
moveSan:
type: string
pv:
type: array
items:
type: string
evalCp:
type: number
description: Centipawn score from the side-to-move's perspective, omitted if mateIn is set
mateIn:
type: integer
description: Moves to mate from the side-to-move's perspective (negative = getting mated), omitted if evalCp is set
engine:
type: string
fenEchoed:
type: string
evalCp:
type: number
description: Centipawn score from the side-to-move's perspective, omitted if mateIn is set
mateIn:
type: integer
description: Moves to mate from the side-to-move's perspective (negative = getting mated), omitted if evalCp is set
- type: object
description: JSON-RPC 2.0 response envelope. `result.content[0].text` is a JSON-encoded string matching the schema in `x-mcp-result-schema`.
properties:
jsonrpc:
const: '2.0'
id:
type:
- string
- number
result:
type: object
properties:
content:
type: array
items:
type: object
properties:
type:
const: text
text:
type: string
x-mcp-result-schema:
type: object
required:
- status
- line
- depthReached
- timedOut
- engine
- fenEchoed
properties:
status:
type: string
enum:
- ok
- checkmate
- stalemate
- draw
line:
type: array
items:
type: object
required:
- ply
- move
- san
- depthReached
properties:
ply:
type: integer
move:
type: string
san:
type: string
depthReached:
type: integer
evalCp:
type: number
description: Centipawn score from the side-to-move's perspective, omitted if mateIn is set
mateIn:
type: integer
description: Moves to mate from the side-to-move's perspective (negative = getting mated), omitted if evalCp is set
depthReached:
type: integer
timedOut:
type: boolean
engine:
type: string
fenEchoed:
type: string
'402':
description: Payment Required
content:
application/json:
schema:
type: object
properties:
x402Version:
type: integer
error:
type: string
accepts:
type: array
x-payment-info:
price:
mode: fixed
currency: USD
amount: '0.01'
protocols:
- x402: {}
/tools/evaluate_position:
post:
operationId: chess-eval_evaluate_position_http
summary: 'Evaluate a chess position with Stockfish: best move, centipawn/mate score…'
tags:
- chess-eval
requestBody:
required: true
content:
application/json:
schema:
type: object
properties:
fen:
type: string
depth:
type: integer
minimum: 1
maximum: 18
multipv:
type: integer
minimum: 1
maximum: 5
required:
- fen
additionalProperties: false
example:
fen: rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1
depth: 10
responses:
'200':
description: Tool result (plain JSON, not MCP-wrapped)
content:
application/json:
schema:
type: object
required:
- status
- bestMove
- pv
- depthReached
- timedOut
- multipv
- engine
- fenEchoed
properties:
status:
type: string
enum:
- ok
- checkmate
- stalemate
- draw
bestMove:
type:
- string
- 'null'
bestMoveSan:
type:
- string
- 'null'
pv:
type: array
items:
type: string
description: Principal variation in SAN
pvUci:
type: array
items:
type: string
depthReached:
type: integer
timedOut:
type: boolean
multipv:
type: array
items:
type: object
required:
- move
- moveSan
- pv
- pvUci
properties:
move:
type: string
moveSan:
type: string
pv:
type: array
items:
type: string
evalCp:
type: number
description: Centipawn score from the side-to-move's perspective, omitted if mateIn is set
mateIn:
type: integer
description: Moves to mate from the side-to-move's perspective (negative = getting mated), omitted if evalCp is set
engine:
type: string
fenEchoed:
type: string
evalCp:
type: number
description: Centipawn score from the side-to-move's perspective, omitted if mateIn is set
mateIn:
type: integer
description: Moves to mate from the side-to-move's perspective (negative = getting mated), omitted if evalCp is set
example:
status: ok
bestMove: d7d5
bestMoveSan: d5
pv:
- d5
- e5
- d4
- c3
- Nc6
- Nf3
- dxc3
pvUci:
- d7d5
- e4e5
- d5d4
- c2c3
- b8c6
- g1f3
- d4c3
depthReached: 10
timedOut: false
multipv:
- move: d7d5
moveSan: d5
pv:
- d5
- e5
- d4
- c3
- Nc6
- Nf3
- dxc3
pvUci:
- d7d5
- e4e5
- d5d4
- c2c3
- b8c6
- g1f3
- d4c3
evalCp: -29
engine: stockfish 10 asm.js
fenEchoed: rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1
perspective: side-to-move
evalCp: -29
'400':
description: Invalid input
content:
application/json:
schema:
type: object
properties:
error:
type: string
message:
type: string
'402':
description: Payment Required
content:
application/json:
schema:
type: object
properties:
x402Version:
type: integer
error:
type: string
accepts:
type: array
x-payment-info:
price:
mode: fixed
currency: USD
amount: '0.01'
protocols:
- x402: {}
/tools/best_line:
post:
operationId: chess-eval_best_line_http
summary: Play out Stockfish's predicted principal variation as SAN moves with a per-ply…
tags:
- chess-eval
requestBody:
required: true
content:
application/json:
schema:
type: object
properties:
fen:
type: string
depth:
type: integer
minimum: 1
maximum: 18
maxPlies:
type: integer
minimum: 1
maximum: 40
required:
- fen
additionalProperties: false
example:
fen: rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1
depth: 10
maxPlies: 4
responses:
'200':
description: Tool result (plain JSON, not MCP-wrapped)
content:
application/json:
schema:
type: object
required:
- status
- line
- depthReached
- timedOut
- engine
- fenEchoed
properties:
status:
type: string
enum:
- ok
- checkmate
- stalemate
- draw
line:
type: array
items:
type: object
required:
- ply
- move
- san
- depthReached
properties:
ply:
type: integer
move:
type: string
san:
type: string
depthReached:
type: integer
evalCp:
type: number
description: Centipawn score from the side-to-move's perspective, omitted if mateIn is set
mateIn:
type: integer
description: Moves to mate from the side-to-move's perspective (negative = getting mated), omitted if evalCp is set
depthReached:
type: integer
timedOut:
type: boolean
engine:
type: string
fenEchoed:
type: string
example:
status: ok
line:
- ply: 1
move: d7d5
san: d5
depthReached: 10
evalCp: -29
- ply: 2
move: e4d5
san: exd5
depthReached: 10
evalCp: 100
- ply: 3
move: c7c6
san: c6
depthReached: 10
evalCp: -52
- ply: 4
move: g1f3
san: Nf3
depthReached: 10
evalCp: 96
depthReached: 10
timedOut: false
engine: stockfish 10 asm.js
fenEchoed: rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1
perspective: side-to-move
'400':
description: Invalid input
content:
application/json:
schema:
type: object
properties:
error:
type: string
message:
type: string
'402':
description: Payment Required
content:
application/json:
schema:
type: object
properties:
x402Version:
type: integer
error:
type: string
accepts:
type: array
x-payment-info:
price:
mode: fixed
currency: USD
amount: '0.01'
protocols:
- x402: {}