Fen Parse

{
  "asOf": "2026-10-12T01:02:03.320Z",
  "black": {
    "bishops": 2,
    "kings": 1,
    "knights": 2,
    "pawns": 8,
    "queens": 1,
    "rooks": 2
  },
  "castling": {
    "blackKingside": true,
    "blackQueenside": true,
    "whiteKingside": true,
    "whiteQueenside": true
  },
  "degraded": false,
  "disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
  "enPassantSquare": null,
  "fiftyMoveRuleReached": false,
  "fullmoveNumber": 1,
  "halfmoveClock": 0,
  "notChecked": [
    "whether the side not to move is in check (an illegal position)",
    "whether the position is reachable by legal play",
    "…2 more"
  ],
  "pieceCount": {
    "black": 16,
    "white": 16
  },
  "problems": [],
  "reasons": [],
  "sideToMove": "white",
  "source": "computed locally (FEN specification)",
  "summary": "Well-formed White-to-move position, move 1.",
  "valid": true,
  "verdict": "VALID_POSITION_STRUCTURE",
  "white": {
    "bishops": 2,
    "kings": 1,
    "knights": 2,
    "pawns": 8,
    "queens": 1,
    "rooks": 2
  }
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://chess-notation.x402tookit.com/fen-parse?fen=rnbqkbnr%2Fpppppppp%2F8%2F8%2F8%2F8%2FPPPPPPPP%2FRNBQKBNR+w+KQkq+-+0+1'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://chess-notation.x402tookit.com/fen-parse?fen=rnbqkbnr%2Fpppppppp%2F8%2F8%2F8%2F8%2FPPPPPPPP%2FRNBQKBNR+w+KQkq+-+0+1' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fchess-notation.x402tookit.com%2Ffen-parse
const res = await pay("https://chess-notation.x402tookit.com/fen-parse?fen=rnbqkbnr%2Fpppppppp%2F8%2F8%2F8%2F8%2FPPPPPPPP%2FRNBQKBNR+w+KQkq+-+0+1");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://chess-notation.x402tookit.com/fen-parse?fen=rnbqkbnr%2Fpppppppp%2F8%2F8%2F8%2F8%2FPPPPPPPP%2FRNBQKBNR+w+KQkq+-+0+1")
    print(res.status_code, res.text)