rein-sdk

Bounded payments for AI agents. One API key. On-chain spend caps the caller can't bypass.

Install

npm install rein-sdk

(Post-hackathon this goes live on npm. Today it lives in the Rein-Arc repo; point your package.json at the GitHub path if you want to try it before publish:)

npm install github:Shunsuke0401/Rein-Arc#main

Quickstart

Get an API key: create an agent in the Rein dashboard, save the REIN_API_KEY from the one-shot credentials modal.

import { Rein } from "rein-sdk";

const rein = new Rein({ apiKey: process.env.REIN_API_KEY! });

const payment = await rein.payments.create({
  to: "0x5D262Ad5F60189Bb21Eb6cF6BCA7Db04F2C01518", // 0x address of a saved payee
  amountUsd: 50,
});

console.log(payment.status); // "confirmed"

What the caps enforce

Every API key is scoped by the permission you set at creation:

• Per-payment cap — a single call over this amount is rejected by the smart account.
• Monthly cap — approximated as N calls × per-payment, reset every 30 days.
• Payee allow-list — if you saved payees, the to address must match one of them. Over-list recipients revert on-chain.

A Rein server compromise cannot widen these. They're pinned in the permission validator on-chain.

API

rein.payments.create({ to, amountUsd, note? })

Sends USDC to a recipient. to must be a raw 0x… address — labels are not accepted. Returns { id, status, amountUsd, to, createdAt }.

rein.agent.status()

Returns agent-level view: name, balance, spent this month, caps, remaining monthly allowance, status.

rein.agent.payees()

Returns saved payees for this permission as [{ id, label }]. Addresses are never returned.

rein.agent.activity({ limit? })

Returns the most recent payment activity as [{ timestamp, direction, counterpartyLabel, amountUsd, status }].

Errors

All SDK errors are ReinError instances with a typed code:

| Code | Meaning | |---|---| | INVALID_API_KEY | Missing, malformed, or revoked key. | | PERMISSION_CAP_EXCEEDED | Amount exceeds the per-payment cap. | | PAYEE_NOT_ALLOWED | Recipient not on the permission's payee allow-list. | | NOT_FOUND | Payee label or resource doesn't exist. | | NETWORK_ERROR | Timeout or transport failure. | | INTERNAL | Server error. |

import { Rein, ReinError } from "rein-sdk";

try {
  await rein.payments.create({
    to: "0x5D262Ad5F60189Bb21Eb6cF6BCA7Db04F2C01518",
    amountUsd: 99,
  });
} catch (err) {
  if (err instanceof ReinError && err.code === "PERMISSION_CAP_EXCEEDED") {
    console.error("Over cap:", err.message);
  }
}

Self-hosted base URL

Override baseUrl if you run your own Rein instance:

const rein = new Rein({
  apiKey: process.env.REIN_API_KEY!,
  baseUrl: "https://my-rein.example.com",
});