Domain Availability Checker

Give this API up to 10 domain names and it will tell you whether each one has a registration record on file with the official registry. It uses RDAP — the modern, structured replacement for WHOIS — so there is no messy free-text parsing. Each domain comes back labeled 'registered', 'unregistered', or 'indeterminate' (when the registry does not support RDAP for that ending). Important: 'unregistered' means no record was found, which usually means the name is available — but reserved or premium names can also return no record. This API tells you registration status only; it does not tell you price, premium status, or whether a registrar will actually let you buy the name.

Call it in 30 seconds

// npm i x402-fetch viem
import { wrapFetchWithPayment } from "x402-fetch";
import { createWalletClient, http } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { base } from "viem/chains";

const account = privateKeyToAccount(process.env.PRIVATE_KEY); // funds USDC on Base
const wallet = createWalletClient({ account, chain: base, transport: http() });
const fetchWithPay = wrapFetchWithPayment(fetch, wallet);

// Pays the $0.01 USDC automatically on the 402, then returns the real response:
const res = await fetchWithPay("https://domain-availability-checker.underscoredone.com/check", { method: "POST" });
console.log(await res.json());

# pip install x402 eth-account httpx
import os, asyncio
from eth_account import Account
from x402.clients.httpx import x402HttpxClient

account = Account.from_key(os.environ["PRIVATE_KEY"])  # funds USDC on Base

async def main():
    async with x402HttpxClient(account=account) as client:
        # x402 handles the 402 -> pay ($0.01 USDC) -> retry automatically
        r = await client.get("https://domain-availability-checker.underscoredone.com/check")
        print((await r.aread()).decode())

asyncio.run(main())

# 1) An unpaid request returns HTTP 402 with the exact payment terms:
curl -i -X POST "https://domain-availability-checker.underscoredone.com/check" \
  -H 'content-type: application/json' \
  -d '{"domains": ["example.com", "mybrand.ai", "coolstartup.io"]}'

# 2) Paying + retrying requires an x402 client that can sign the USDC
#    authorization (curl alone cannot). See the JS / Python tabs below.

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