Docs

How Nucleo works.

Every number is read from the catalogs or a live 402; the AI only ranks and explains.

The index

Nucleo pages through the public x402 discovery catalogs, the Coinbase CDP Bazaar and the PayAI Bazaar, strips every resource to what matters (URL, method, description, price, asset, network, payTo, last update) and groups it by host. A full pass reads around 120,000 entries; the market fills as it goes and re-syncs every few hours. Nothing in the directory is typed by hand.

Categories come first from rules over each listing's own text, then Nucleo Core refines them and writes a one-line summary per host, in batches, with a daily cap.

How agents pay

  • The agent calls the endpoint and gets 402 Payment Required with a PAYMENT-REQUIRED header (base64 JSON, x402 v2) or an accepts body (v1): scheme, network, amount, asset, payTo, timeout.
  • It signs the payment: EIP-3009 TransferWithAuthorization for stablecoins, or a Permit2 PermitWitnessTransferFrom for plain ERC-20s.
  • It retries with PAYMENT-SIGNATURE. The facilitator verifies and settles; the response carries a PAYMENT-RESPONSE receipt with the transaction hash.

Probe any endpoint on its project page to read its real 402 before an agent pays for it.

Host an API behind Nucleo

Dashboard → Launch your API: paste the https URL of your API, a price per call, the wallet that earns, and optionally an auth header Nucleo should add when forwarding (stored encrypted). Nucleo answers 402 at /x/<name>/…, verifies the payment, forwards the request to your API and settles only when your API answers with a status below 400. Earnings go to your payTo; Nucleo takes no cut. Limits: https only, public host, 1 MB request, 25 s timeout, no redirects.

List a self-hosted API

If your server already answers 402 with x402 requirements, submit its URL in the Dashboard. Nucleo probes it live; if the 402 is valid it waits for the owner's review and then joins the market under your host, marked "listed here". Listing is free. Hosts picked up from the catalogs appear on their own.

Payment rails

  • USDG on Robinhood Chain (0x5fc5360D0400a0Fd4f2af552ADD042D716F1d168, 6 decimals): EIP-3009, one signature, no approval, no gas for the payer.
  • $NUCLEO on Robinhood Chain: exact scheme with assetTransferMethod: "permit2". The payer approves the canonical Permit2 contract once (needs a little ETH for gas), then each call is one signature. The amount is priced from the Pons curve and the ETH price at request time.
  • USDC on Base: EIP-3009, when the relayer holds gas on Base or a remote facilitator covers it.

The facilitator

Nucleo runs its own. Verification checks the EIP-712 signature against the chain's domain, the validity window, the amount, the recipient, the payer's balance, the nonce (EIP-3009 authorizationState, Permit2 nonceBitmap) and the Permit2 allowance. Settlement is submitted by a relayer wallet that only pays gas; tokens move straight from the payer to payTo. Endpoints: GET /facilitator/supported, POST /facilitator/verify, POST /facilitator/settle.

The gateway

/x/<host>/<path> proxies any indexed host transparently: the 402 and the payment headers pass through, the payment goes to the owner, Nucleo only counts the call. /x/<name>/… (no dot) is an API hosted behind Nucleo's own 402.

Public API v1

  • GET /api/v1/stats totals, networks, categories, sources, gateway counts.
  • GET /api/v1/projects with q, network, category, sort (relevance, endpoints, cheap, calls), page, limit.
  • GET /api/v1/projects/{host} one host with its endpoints.

Free, no key. Agent calls (/api/market/find, /api/market/explain) are counted per identity per day.

Pro API

GET /api/v1/pro/endpoints?q= searches at endpoint level across every indexed API and is paid per call with x402 to the treasury wallet, in USDG or $NUCLEO. It answers 503 until the owner sets a treasury.

$NUCLEO and tiers

Search, probes, the gateway, hosting and listings are free for everyone. Agent calls are counted per day; holding $NUCLEO raises the count: Free, Holder (≥ 0.1% of supply) and Holder+ (≥ 0.5%), checked against the wallet balance after one signed message, no transaction. Buybacks from the studio buy $NUCLEO on its Pons curve with the dead address as receiver, in one transaction, and are listed publicly.

Nucleo Core

The agent behind "Ask Nucleo" and "Nucleo reads this host". It only ranks and explains data the server already computed; it never invents a host, a price or a number, and it is called Nucleo Core everywhere.

What Nucleo never does

  • Hold or route your funds. Payments settle payer → owner on-chain.
  • Store your keys. The relayer and burn wallets are separate gas wallets, encrypted at rest; your agent's key never leaves your machine.
  • Type numbers by hand. If a count cannot be read from the catalogs, the chain or a live 402, it is not shown.