Ask Bitcoin questions in Ethereum language.

curl -i https://api.nativebtc.org/v1/block-height

# The 402 response includes:
# Payment-Required: eyJ4NDAy...
#
# Decode it:
node -e "const h=process.argv[1]; console.log(JSON.parse(Buffer.from(h,'base64').toString('utf8')))" "PASTE_PAYMENT_REQUIRED"

Shows price, supported networks, USDC token, and pay-to address before a bot spends.

npm i @x402/fetch @x402/evm viem

import { wrapFetchWithPaymentFromConfig } from "@x402/fetch";
import { ExactEvmScheme } from "@x402/evm";
import { privateKeyToAccount } from "viem/accounts";

const account = privateKeyToAccount(process.env.EVM_PRIVATE_KEY);

const fetchWithPayment = wrapFetchWithPaymentFromConfig(fetch, {
  schemes: [
    { network: "eip155:*", client: new ExactEvmScheme(account) }
  ]
});

const res = await fetchWithPayment("https://api.nativebtc.org/v1/rpc", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    jsonrpc: "2.0",
    id: 1,
    method: "fastpath_feeLadder",
    params: [{ targetBlocks: 6 }]
  })
});

console.log(await res.json());

Works with Base, Polygon, Arbitrum, or World USDC if the wallet has funds.

const res = await fetchWithPayment(
  "https://api.nativebtc.org/v1/bitcoin/insight",
  {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({
      txid: "PASTE_TXID",
      address: "bc1q...",
      targetBlocks: 6,
      action: "analyze"
    })
  }
);

const answer = await res.json();

console.log(answer.verdict);
console.log(answer.summary);
console.log(answer.bump);

Use this when the bot wants a decision, not a raw mempool dump.

const res = await fetchWithPayment(
  "https://api.nativebtc.org/v1/template/fee-ladder",
  {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({ targetBlocks: 6 })
  }
);

console.log(await res.json());

// Public capability docs:
// curl https://api.nativebtc.org/v1/template/capabilities

Use REST when your bot wants one focused answer instead of JSON-RPC.

const analysis = await fetchWithPayment(
  "https://api.nativebtc.org/v1/bitcoin/insight",
  {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({
      txid: "PASTE_ORIGINAL_TXID",
      targetBlocks: 1,
      action: "analyze"
    })
  }
).then((r) => r.json());

if (analysis.bump?.available) {
  // Build and sign the replacement in your own wallet.
  const signedReplacementHex = "02000000...";

  const relayed = await fetchWithPayment(
    "https://api.nativebtc.org/v1/bitcoin/insight",
    {
      method: "POST",
      headers: { "content-type": "application/json" },
      body: JSON.stringify({
        txid: "PASTE_ORIGINAL_TXID",
        action: "broadcast_signed_replacement",
        signedReplacementHex
      })
    }
  ).then((r) => r.json());

  console.log(relayed.broadcast);
}

FastPath plans and relays only. Your wallet signs; the API never holds keys.