Reins MCP

Let any AI agent trade through a Mandate on Arc: an MCP server, a JavaScript SDK and a reference agent.

A Mandate is a smart contract that holds an agent's USDC under rules the agent can't break: a cap on every trade, a fair-price check against Chainlink, a loss limit with a public stop-loss, an expiry, and no way to move money out. The contracts are in reins-contracts. This repo is how an agent uses one.

The agent never needs to be trusted. It holds only its own trading key, and the contract decides what that key may do. A trade that breaks a rule is refused on-chain, and the refusal comes back to the agent as a plain sentence naming the rule, so it can adjust instead of retrying blindly.

Part of Reins · app at app.reins.one

The MCP server

Three tools for any MCP client (Claude Desktop, Claude Code, or any agent framework that speaks MCP):

A refused trade returns { "ok": false, "rule": "TradeTooLarge", "reason": "…" } rather than a raw revert.

Use it from Claude Desktop

git clone https://github.com/onreins/reins-mcp && cd reins-mcp && npm install

Then add it to claude_desktop_config.json:

{
  "mcpServers": {
    "mandate": {
      "command": "node",
      "args": ["/path/to/reins-mcp/src/mcp-server.js"],
      "env": {
        "MANDATE_ADDRESS": "0xYourMandate",
        "MANDATE_AGENT_KEY": "0xTheAgentsTradingKey",
        "MANDATE_NETWORK": "testnet"
      }
    }
  }
}

Create a Mandate and its agent key in the app at app.reins.one, or with createMandate below.

Related MCP server: Arcade Agent MCP

The SDK

import { MandateClient, createMandate } from "./src/sdk.js";

const mandate = new MandateClient({ publicClient, wallet, address });

await mandate.status();                                   // money, holdings, rules, headroom
await mandate.price("EURC");                              // { usd, updatedAt }
await mandate.trade({ from: "USDC", to: "EURC", amount: "5" });
// → { sold, bought, equityUsd }, or throws with err.mandate = { rule, reason }

publicClient and wallet are viem clients for Arc; the wallet holds the agent's key, and reading needs no wallet at all.

createMandate creates and funds one through the factory, with rules in plain units:

const address = await createMandate({
  publicClient, ownerWallet, factory, venue, base: USDC,
  name: "my first agent",
  agent: agentAddress,
  rules: { maxTradeUsd: 2, maxLossPercent: 10, maxSlippagePercent: 1, expiresAt: "2026-12-31" },
  assets: [{ token: EURC, feed: EURC_USD_FEED }],
  deposit: 5,
});

The reference agent

examples/fx-reversion.js trades EUR/USD reversion through a Mandate: when EURC is cheap in the Uniswap pool against Chainlink by more than the pool fee plus a margin, it buys; when rich, it sells. Every decision is logged with its reason.

MANDATE_ADDRESS=0x… MANDATE_AGENT_KEY=0x… npm run agent:fx -- --once

It is a worked example, not a profitable strategy. We measured it on live Arc mainnet data: over 23.8 hours the pool moved 33.7bp in total, against a 10bp round-trip cost, so every threshold at or above cost fired zero trades. It's here to show how an agent drives a Mandate, and because its refusals are what the live testnet run exercised.

Settings: AGENT_EDGE_BPS (default 15), AGENT_TRADE_USD (default: the Mandate's limit), AGENT_INTERVAL_SEC (default 60).

Tests

npm install
npm run chain        # terminal 1: a local node
npm test             # terminal 2: 20 tests

They run the MCP server through a real MCP client against freshly deployed contracts: status, prices and trades; every refusal named instead of dumped as a raw revert; tokens that return nothing or restrict who may hold them; and the reference agent's decisions. compiled/ holds the contract builds the tests deploy, produced by reins-contracts.

License

MIT