@priors/x402

x402 on Robinhood Chain (eip155:4663) in USDG, on top of the official @x402/* 2.27 packages, plus credit: when an agent is short, it can borrow the gap from its Priors line.

• registerUsdg(scheme): price: "$0.05" on eip155:4663 means USDG (6 decimals, EIP-712 domain "Global Dollar" v1).
• priorsFacilitator({ apiKey }): config for the official HTTPFacilitatorClient, pointed at https://facilitator.priors.trade, with your merchant key as Authorization: Bearer … on verify/settle/supported.
• createPayer({ signer, … }).pay(url, init): a fetch that pays x402 USDG (v2, and legacy v1 robinhood bodies) and borrows the gap when you allow it.
• robinhood: the constants (network and its legacy v1 name, chain id, USDG address and decimals, EIP-712 domain, facilitator URL, public RPC URL, Priors pool, lens, identity registry and stock vault addresses).

npm i @priors/x402 @x402/core @x402/evm ethers

The examples below also use optional packages: @x402/express (Express), @x402/hono (Hono), and @x402/mcp with @modelcontextprotocol/sdk (the paid MCP tool). Install the ones you use.

Merchant: Express

import express from "express";
import { paymentMiddleware, x402ResourceServer } from "@x402/express";
import { ExactEvmScheme } from "@x402/evm/exact/server";
import { HTTPFacilitatorClient } from "@x402/core/server";
import { registerUsdg, priorsFacilitator, robinhood } from "@priors/x402";

const server = new x402ResourceServer(new HTTPFacilitatorClient(priorsFacilitator({ apiKey: process.env.PRIORS_MERCHANT_KEY })))
  .register(robinhood.network, registerUsdg(new ExactEvmScheme()));

const app = express();
app.use(paymentMiddleware({
  "GET /report": {
    accepts: { scheme: "exact", price: "$0.05", network: robinhood.network, payTo: "0xYourAddress" },
    description: "One report, 0.05 USDG",
  },
}, server));
app.get("/report", (req, res) => res.json({ report: "…" }));
app.listen(3000);

The merchant key comes from registering your payTo with the facilitator (POST /merchants/register, or the merchant page of x402.priors.trade). createResourceServer({ apiKey }) does the first two lines in one call.

Merchant: Hono

import { Hono } from "hono";
import { paymentMiddleware } from "@x402/hono";
import { createResourceServer, robinhood } from "@priors/x402";

const app = new Hono();
app.use(paymentMiddleware({
  "GET /report": {
    accepts: { scheme: "exact", price: "$0.05", network: robinhood.network, payTo: "0xYourAddress" },
    description: "One report, 0.05 USDG",
  },
}, createResourceServer({ apiKey: process.env.PRIORS_MERCHANT_KEY })));
app.get("/report", (c) => c.json({ report: "…" }));
export default app;

Merchant: a paid MCP tool (@x402/mcp)

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { createPaymentWrapper } from "@x402/mcp";
import { createResourceServer, robinhood } from "@priors/x402";

const resourceServer = createResourceServer({ apiKey: process.env.PRIORS_MERCHANT_KEY });
await resourceServer.initialize();
const accepts = await resourceServer.buildPaymentRequirements({
  scheme: "exact", network: robinhood.network, payTo: "0xYourAddress", price: "$0.01",
});
const paid = createPaymentWrapper(resourceServer, { accepts });

const mcp = new McpServer({ name: "my-paid-tools", version: "1.0.0" });
mcp.tool("quote", "A price quote. Costs 0.01 USDG.", {}, paid(async () => ({ content: [{ type: "text", text: "42" }] })));
await mcp.connect(new StdioServerTransport());

An agent pays it with @x402/mcp's client and this package's USDG client: wrapMCPClientWithPayment(mcpClient, createUsdgClient({ signer, maxPrice: "$0.05" }), { autoPayment: true }).

Merchant: check who is paying (record gate)

The payer's Priors record is what it has borrowed and repaid on Robinhood Chain, and whether it ever defaulted. recordGate reads it before the facilitator sees the payment. A payment the merchant's policy refuses is never verified or settled: no money moves, and the client gets the usual 402. The reason (priors_payer_defaulted, priors_record_too_short, priors_score_too_low, priors_price_not_entitled, priors_record_unavailable) is the error field of its PAYMENT-REQUIRED header (base64 JSON), not the body.

import { createResourceServer, recordGate } from "@priors/x402";

const server = createResourceServer({ apiKey: process.env.PRIORS_MERCHANT_KEY });
recordGate({ refuseDefaulted: true, minRepaid: 1 }).attach(server); // then paymentMiddleware(routes, server) as above

On a local fork. Read the record from the fork, not mainnet, and settle on the fork: facilitator.priors.trade only settles on Robinhood Chain itself. createResourceServer takes any x402 v2 facilitator client as facilitatorClient; agent001's sandbox runs one that pays the gas from a fork-only wallet (src/facilitator-local.mjs).

const server = createResourceServer({ facilitatorClient: myForkFacilitator });
recordGate({ source: "chain", rpc: "http://127.0.0.1:8545", minRepaid: 1 }).attach(server);

| option | default | | |---|---|---| | refuseDefaulted | true | refuse a payer whose agent defaulted on a Priors loan | | minRepaid | 0 | repaid Priors loans the payer must have | | minScore | none | Priors Score v2 the payer must have (on-chain score with source: "chain") | | source | "api" | "api": https://priors.trade/api/check by the payer's address (every agent it owns or declared as its payment wallet; no key). "chain": Priors pool v2 read over rpc, for the agent the payer names in the X-Priors-Agent header, after checking the paying address controls it. Use it on a fork, or to depend on no Priors service | | rpc, pool | public RPC, the published pool | for source: "chain" | | tiers, basePrice | none | prices by record: tiers: [{ minRepaid: 3, price: "$0.01" }], basePrice: "$0.02" | | cacheSeconds | 60 | how long a payer's record is reused | | onDecision | none | called with { payer, record, ok, reason } for each payment |

A record that cannot be read refuses rather than serves on a guess.

Prices by record. Give the route price: gate.tierPrice(). A client states its address in X-Payer (and its agent in X-Priors-Agent with source: "chain") to be quoted its tier. That statement is only a request: when the payment arrives, the gate reads the record of the address that actually signed it. It refuses a payment below that payer's own price, so claiming someone else's record gets nothing.

const gate = recordGate({ basePrice: "$0.02", tiers: [{ minRepaid: 3, price: "$0.01" }] }).attach(server);
// routes: { "GET /report": { accepts: { scheme: "exact", price: gate.tierPrice(), network: "eip155:4663", payTo } } }

Agent: pay, and borrow the gap

import { ethers } from "ethers";
import { createPayer, robinhood } from "@priors/x402";

const provider = new ethers.JsonRpcProvider(robinhood.rpcUrl);
const signer = new ethers.Wallet(process.env.AGENT_KEY, provider); // the agent's wallet (and its Priors controller)

const payer = createPayer({
  signer,
  maxPrice: "$0.10",          // most one call may cost; a dearer 402 is refused before anything is signed
  // optional credit: borrow what the wallet is short of, from the agent's Priors line
  pool: robinhood.pool, agentId: 1234, maxBorrow: "$5",
});

const { response, paid, borrowed, loanId, dueAt } = await payer.pay("https://api.example.com/report");
console.log(response.status, await response.json(), { paid, borrowed, loanId, dueAt });
// once the agent has been paid by its client:
await payer.settleLoans(); // repays open loans, earliest due first; do it before dueAt

To a merchant whose record gate reads the chain, name the agent the wallet controls: payer.pay(url, { headers: { "x-priors-agent": "1234" } }). A refusal comes back as a 402 whose reason is the error field of the PAYMENT-REQUIRED header.

Amounts: a bigint or integer is atomic USDG (6 decimals: 100000n = $0.10); a string with $ is dollars.

A result also carries the requirement it paid, its x402Version and, on success, the decoded settlement (PAYMENT-RESPONSE) when the merchant sent one. Other createPayer options: maxValiditySeconds (at most 600, the default), asset (a USDG address for a fork or test token; default the pool's usdg(), else mainnet USDG), fetchImpl, pendingRetries (default 6), maxSleepMs (longest wait between resends, default 30 s) and sleep.

What pay() promises (the rules of sdk/float.mjs, unchanged)

• maxPrice (default $0.10) is checked before anything is read, signed or borrowed.
• Borrowing happens only when the wallet is short, a pool and agentId are given, and the price is within maxBorrow (default 0: never). It draws max(shortfall, pool minimum loan), refuses above maxBorrow or the pool's maxLoan, caps the fee at the pool's quote (or maxFee), and simulates the borrow first. A borrow that was sent and whose answer was lost (the broadcast's or the receipt's) may have mined: it throws BORROW_UNCONFIRMED with borrowed set, loanId: null, unconfirmed: true and the tx hash when known. Count it, check the agent's loans, and repay before the due date.
• Term: 7 days by default, clamped into the pool's range; an explicit termSeconds above the pool's maximum is refused. The result's dueAt is when the loan is due; three days later anyone can mark it defaulted, and the agent's record is burnt.
• Authorization window: at most 600 s, whatever maxTimeoutSeconds the merchant asks. The payload's accepted stays the merchant's requirement verbatim.
• One signature per purchase. While the merchant answers "pending" (v2 settlement_pending, or a legacy {pending:true} body) the same signed payment is resent, up to 6 times, honouring Retry-After. If it is still pending, the result is { pending: true, paymentHeaders }: call payer.resend(url, paymentHeaders) later, and do not call pay() again for the same purchase. A payer also remembers its unsettled payments: a later pay() for the same purchase (the method; the URL as the merchant reads it: without its fragment, query fields in name order, + and %20 alike, escapes in one case; and the body: a JSON body by its value, so key order, whitespace and how a number is written do not count, and a urlencoded or multipart form by its fields; purchaseKey(request) gives it) resends that one (resent: true) until it expires, plus SKEW_SECONDS (60 s, exported) for a chain clock behind this machine's. That memory is per payer and per process: pass onSigned(s) to createPayer to record each payment before it leaves (s.paymentHeaders, s.validBefore, s.price, s.purchase), so a new process can resend it instead of signing again. If onSigned throws, the payment is not sent: pay() rejects with NOT_RECORDED and nothing can be settled. @priors/mcp does this with a state file.
• Legacy v1 402 bodies (network: "robinhood", X-PAYMENT) are paid the way sdk/float.mjs pays them.
• No redirects. Requests go out with redirect: "manual" unless you pass another redirect in init (redirect: undefined counts as none): a signed payment never travels to a host you did not name, and a 3xx comes back as the answer.
• Bounded. Bodies are read up to 256 KB (readCapped). timeoutMs (60 s by default; 0 = none) bounds each request and signal the whole call; a timeout once the payment is out returns { pending: true, timedOut: true, paymentHeaders }, and a dropped connection { pending: true, transportError: true, error, paymentHeaders }: never an error once the payment may be out. An error thrown after a loan or a signature carries borrowed, loanId, dueAt and signed.
• One payment at a time per payer: two concurrent pay() calls on a short wallet do not both borrow the gap.
• signed: every result of a signed payment carries signed: { paymentHeaders, validBefore }. Until validBefore the merchant can still cash it, so a retry of the same purchase must resend these headers.

Refusals throw a PayError with a code: PRICE_ABOVE_MAX_PRICE, PRICE_ABOVE_MAX_BORROW, MIN_LOAN_ABOVE_MAX_BORROW, ABOVE_MAX_LOAN, TERM_OUT_OF_RANGE, FEE_TOO_HIGH, NO_POOL, NO_USDG_REQUIREMENT, BAD_402, BORROW_WOULD_REVERT, BORROW_UNCONFIRMED (not a refusal: the borrow was sent, and may have opened a loan), NO_SIGNER, NO_PROVIDER, NO_FETCH, UNSUPPORTED_TRANSFER_METHOD (a requirement that is not EIP-3009), NOT_CONTROLLER (repayLoan, settleLoans). The credit helpers add LOAN_SIZE_OUT_OF_RANGE (quoteBorrow, borrowLine), LOAN_NOT_ACTIVE, INSUFFICIENT_USDG, REPAY_WOULD_REVERT (repayLoan) and NO_STOCK_VAULT (stockPosition, stockAssets).

Why pay() is not just @x402/fetch's wrapFetchWithPayment

It uses the same parts (x402Client, x402HTTPClient, ExactEvmScheme), but writes the request loop out, because the wrapper (2.27) cannot keep the rules above: it can only act inside payload creation, so a borrow refusal would surface as a generic "Failed to create payment payload" error; when a response hook reports recovered it signs a fresh payload while the first may still settle (two payments for one call); it has no pending loop and never hands back the signed header; and it cannot route v1 robinhood bodies. If you never borrow, createUsdgClient() gives you an x402Client with the same USDG allowance, price cap and 600 s window for wrapFetchWithPayment:

import { wrapFetchWithPayment } from "@x402/fetch";
import { createUsdgClient } from "@priors/x402";
const fetchWithPay = wrapFetchWithPayment(fetch, createUsdgClient({ signer, maxPrice: "$0.10" }));

Credit helpers

@priors/x402/credit has the Priors v2 pieces the MCP server uses: creditContracts, creditStatus, quoteBorrow, borrowLine, repayLoan, settleLoans, balances, borrowGap, plus poolContract, explainRevert (a revert as Name(args)), LOAN_STATUS and the ABIs (POOL_ABI, LENS_ABI, ERC20_ABI, STOCK_VAULT_ABI). repayLoan pays only a loan of an agent the signer controls (owner or pool delegate); any other loan is refused with NOT_CONTROLLER before anything is sent.

Stock lines (the Priors stock vault, robinhood.stockVault, backs a line with the agent's own stock tokens; creditContracts reads it unless addresses.stockVault says otherwise): creditStatus carries collateral { token, amount, value (what the vault prices them at, null while it will not), ltvBps, borrowRoom, hold (0, or why new loans wait: STOCK_HOLDS), holdReason, status, closing } for a stock line (null for any other), and its available is the smaller of the pool's figure and borrowRoom (stockCollateral(c, id, sponsor) reads that object on its own). stockPosition(c, id, assets?) and stockAssets(c, assets) read one position and the accepted tokens (price, whether the vault lends now, LTV).

Source

github.com/priors-agents/priors, MIT. The facilitator, its merchant sign-up and the live settlements are at x402.priors.trade.