Agents · pay a 402
The Nucleo CLI is a complete paying agent: GET → 402 → sign → retry, and it prints the PAYMENT-RESPONSE receipt. Use a small, separate wallet.
$ npm i -g nucleo-cli $ export NUCLEO_PAYER_KEY=0x… # the paying wallet (USDG on Robinhood Chain, or USDC on Base) $ nucleo find "weather forecast for Seattle" $ nucleo pay https://weather.example/forecast?q=Seattle $ nucleo pay https://nucleoagent.com/x/some-hosted-api/path --prefer usdg $ nucleo approve 0x…NUCLEO # one-time Permit2 approval to pay in $NUCLEO
In code, the official x402 fetch wrapper does the same: @x402/fetch with @x402/evm and a viem account.
import { wrapFetchWithPayment } from "@x402/fetch";
const fetchPaid = wrapFetchWithPayment(fetch, account); // viem account
const r = await fetchPaid("https://api.example.com/v1/thing");Servers · answer a 402
Two ways to sell. Host behind Nucleo: paste your URL and a price in the Dashboard, Nucleo answers 402, verifies, forwards and settles. Or self-host with the x402 middleware and get listed.
import express from "express";
import { paymentMiddleware } from "@x402/express";
app.use(paymentMiddleware({
"GET /forecast": { price: "$0.002", network: "eip155:4663", payTo: "0xYourWallet" },
}, { facilitator: { url: "https://nucleoagent.com/facilitator" } }));Packages: @x402/express, @x402/core, @x402/evm, @x402/fetch; Next.js, Hono, Fastify, Go and Python middlewares exist in the x402 repositories. Once it answers 402, list it in the Dashboard; Nucleo probes it first.
Nucleo API · find and read
Free, no key, cached five minutes.
GET /api/v1/stats
GET /api/v1/projects?q=weather&network=base&category=data&sort=cheap&page=1
GET /api/v1/projects/{host}
GET /api/market/candidates?task=… # the index candidates for a task
POST /api/market/find { "task": "…" } # Nucleo's picks, streamed (SSE), counts against the daily quota
POST /api/market/probe { "url": "…" } # live 402 read
GET /api/v1/pro/endpoints?q=… # endpoint-level search behind a 402 (paid per call)Gateway
Every indexed host is reachable through one prefix; the 402 and the payment headers pass through untouched.
https://nucleoagent.com/x/<host>/<path> # transparent proxy to an indexed host https://nucleoagent.com/x/<name>/<path> # an API hosted behind Nucleo's own 402
CORS is open and PAYMENT-REQUIRED / PAYMENT-RESPONSE are exposed, so browser agents work too.