ToolVet
75trust / 100

Btc Tx Context

by Preflight in Onchain & crypto

x402 APIPassing, checked 2 h ago

Call before signing a Bitcoin transaction when you need chain context for its inputs: whether each prevout exists, whether it is already spent, its value in sats and its confirmations. Resolves up to 10 inputs against a public explorer at about one request per second, so a full batch can take over 20 seconds; figures reflect chain state at checked_at. Describes on-chain facts with source links; never advises whether to sign.

POST
https://preflight402.com/v1/btc/tx-context
Price
$0.1
per call in USDC
Uptime
100%
last 30 days
Response time
627 ms
1.1 s slowest 5%
Last check
Passed
2 h ago, next any minute now

Run a free test callHow to call it

Reliability

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Status and outage history · Atom feed · Watch with other listings

How to call it

POST https://preflight402.com/v1/btc/tx-context

Each call costs $0.1 in USDC on Base, paid with the request over x402.

Run a free test callOne unpaid request, the way an agent sends it. You see the payment challenge it gets back. Nothing is charged.

Example request

From the listing.

POST https://preflight402.com/v1/btc/tx-context
content-type: application/json

{
  "inputs": [
    {
      "txid": "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
      "vout": 0
    }
  ]
}

Parameters

ParameterTypeRequiredDescription
inputsarray of objectYes
networkstringNo One of: mainnet, testnet. Default: "mainnet".

Example response

The provider's example. We can't check it without paying.

{
  "checked_at": "2026-09-11T12:00:00Z",
  "disclaimer": "Chain state at checked_at, from a third-party explorer. Not a recommendation to sign.",
  "inputs": [
    {
      "confirmations": 912345,
      "exists": true,
      "official_url": "https://blockstream.info/tx/4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b?output:0",
      "script_pubkey": "4104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac",
      "spent": false,
      "txid": "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
      "value_sats": 5000000000,
      "vout": 0
    }
  ],
  "network": "mainnet",
  "source": "blockstream.info",
  "total_input_sats": 5000000000
}

Call it from code

The curl command shows the payment challenge. The JavaScript and Python versions pay and call, and never pay more than $0.1.

curl: see the payment challenge
# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://preflight402.com/v1/btc/tx-context' \
  -H 'content-type: application/json' \
  --data-raw '{"inputs":[{"txid":"4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b","vout":0}]}'

# 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://preflight402.com/v1/btc/tx-context' \
  -H 'content-type: application/json' \
  --data-raw '{"inputs":[{"txid":"4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b","vout":0}]}' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode
JavaScript: pay and call
// 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 $0.1 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.1" });
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 $0.1 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fpreflight402.com%2Fv1%2Fbtc%2Ftx-context&method=POST
const res = await pay("https://preflight402.com/v1/btc/tx-context", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "inputs": [
      {
        "txid": "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
        "vout": 0
      }
    ]
  }),
});
console.log(res.status, await res.text());
Python: pay and call
# 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 $0.1 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.1"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://preflight402.com/v1/btc/tx-context",
        json={
            "inputs": [
                {
                    "txid": "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b",
                    "vout": 0,
                },
            ],
        },
    )
    print(res.status_code, res.text)

Security scan

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