# Chess Masters Opening Explorer

> Chess Masters Opening Explorer is a paid API for AI agents from chess402.vercel.app, paid per call via x402, $0.003/call, status unknown (last checked 2026-09-15).

Returns top moves, win/draw/loss statistics, and recent top master games for a given chess position from the Lichess masters database

## Facts

- Endpoint: POST https://chess402.vercel.app/api/masters
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/chess402-vercel-app-1f34e07d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_jzKpgkVFgk03PLgbTl6Sy

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability chess402-vercel-app-1f34e07d -d '<json body>'
```

Example prompt: What are the top master-level moves for the position after 1.e4 e5 2.Nf3 Nc6 — show me the win/draw/loss rates and a few recent grandmaster games from the Lichess masters database.

## When to prefer this

Use this endpoint when you need opening theory data specifically from master-level (grandmaster/IM) games rather than general player games. Prefer this over a general opening explorer when the user wants high-quality move statistics validated by top-level play, or wants to see how real grandmasters have handled a position. Choose the Stockfish sibling endpoint instead if the user wants engine evaluation rather than historical human game data.

## Known failure modes

- Invalid FEN or move sequence returns an error with no data
- Position not found in masters database returns empty move list
- Malformed request body causes a 400 error
- Network timeout or Lichess API unavailability causes a 503 or 504 error
- Position with very few master games may return sparse or no statistics

## How this service works

Masters opening explorer for a position. Returns top moves, win/draw/loss rates, and recent top master games from the Lichess masters database.

## Output

A list of top moves played from the given position in master games, each with win/draw/loss counts and percentages, plus a selection of recent top master games featuring that position including player names, results, and game references.

## Example request

```json
{
 "input": {
  "body": {
   "fen": "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
   "moves": 10,
   "topGames": 4
  },
  "type": "http",
  "method": "POST",
  "bodyType": "json"
 }
}
```

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "fen": {
   "type": "string",
   "maxLength": 100,
   "minLength": 15,
   "description": "Standard FEN position string, e.g. 'rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1'"
  },
  "play": {
   "type": "string",
   "maxLength": 500,
   "description": "Comma-separated UCI move sequence to apply to the FEN before lookup (e.g. 'e2e4,e7e5')."
  },
  "moves": {
   "type": "integer",
   "maximum": 50,
   "minimum": 1,
   "description": "Max number of top moves to return. Default 12."
  },
  "since": {
   "type": "integer",
   "maximum": 2100,
   "minimum": 1500,
   "description": "Include games from this year onward."
  },
  "until": {
   "type": "integer",
   "maximum": 2100,
   "minimum": 1500,
   "description": "Include games up to this year."
  },
  "topGames": {
   "type": "integer",
   "maximum": 15,
   "minimum": 0,
   "description": "Number of recent top games to include. Default 4."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "black": 198217,
  "draws": 311203,
  "moves": [
   {
    "san": "Nf3",
    "uci": "g1f3",
    "game": null,
    "black": 64210,
    "draws": 98421,
    "white": 152340,
    "opening": {
     "eco": "C42",
     "name": "Russian Game"
    },
    "averageRating": 2434
   }
  ],
  "white": 482141,
  "opening": {
   "eco": "C20",
   "name": "King's Pawn Game"
  },
  "topGames": [
   {
    "id": "Sxov6E94",
    "uci": "g1f3",
    "year": 2019,
    "black": {
     "name": "Carlsen, M.",
     "rating": 2882
    },
    "month": "2019-08",
    "white": {
     "name": "Caruana, F.",
     "rating": 2818
    },
    "winner": "white"
   }
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/chess402-vercel-app-1f34e07d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from chess402.vercel.app](https://www.zero.xyz/host/chess402.vercel.app/llms.txt)