Tool Output Guard

{
  "mode": "tool-output-guard",
  "paid_sats": 20,
  "payment_hash": "x402:<sha256 hex>",
  "receipt": {
    "payload": {
      "at": "<ISO 8601 time>",
      "kid": "<signing key id>",
      "mode": "tool-output-guard",
      "payment_hash": "x402:<sha256 hex>",
      "v": 1,
      "verdict_sha256": "<sha256 hex of the verdict>"
    },
    "signature": "<base64url Ed25519 signature>"
  },
  "verdict": {
    "decision": "allow",
    "reasons": [],
    "rule": "block if data-sending request >= 0.7, or orders to the agent >= 0.7 with off-topic or sending >= 0.5 ; review if any score >= 0.4 ; otherwise allow",
    "scores": {
      "addresses_agent": 0.01,
      "exfiltration": 0.01,
      "off_purpose": 0.02
    }
  }
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://verdict.kechlab.com/v1/tool-output-guard' \
  -H 'content-type: application/json' \
  --data-raw '{"output":"Paris: 14 C, light rain, wind 12 km/h.","purpose":"Current weather for a city","tool_name":"get_weather"}'

# 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 - -X POST 'https://verdict.kechlab.com/v1/tool-output-guard' \
  -H 'content-type: application/json' \
  --data-raw '{"output":"Paris: 14 C, light rain, wind 12 km/h.","purpose":"Current weather for a city","tool_name":"get_weather"}' \
  | 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 $0.0132 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.0132" });
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 $0.0132 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fverdict.kechlab.com%2Fv1%2Ftool-output-guard&method=POST
const res = await pay("https://verdict.kechlab.com/v1/tool-output-guard", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "output": "Paris: 14 C, light rain, wind 12 km/h.",
    "purpose": "Current weather for a city",
    "tool_name": "get_weather"
  }),
});
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 $0.0132 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.0132"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://verdict.kechlab.com/v1/tool-output-guard",
        json={
            "output": "Paris: 14 C, light rain, wind 12 km/h.",
            "purpose": "Current weather for a city",
            "tool_name": "get_weather",
        },
    )
    print(res.status_code, res.text)