Vantic MCP server

Vantic

A spending firewall and permission layer for AI agents. Give your agent a signed budget it can't exceed — even if it gets prompt-injected — and get a tamper-proof receipt for everything it does.

Zero dependencies · TypeScript · Ed25519 + W3C DIDs · works with MCP, LangChain, or any tool-calling agent.

The problem

Your AI agent can hold a wallet and call payment APIs. That's useful — and dangerous. One prompt injection from a poisoned web page, one hallucination, one bug, and your agent pays the wrong party. This is a documented, actively-exploited failure mode: agents tricked into wiring funds to attacker-controlled accounts.

What Vantic does

You issue your agent a signed mandate — a budget, a per-transaction cap, allowed actions, and an allowlist of who it may pay — and wrap its money-moving calls (purchase, subscribe, transfer, pay-per-use, payout, refund — any action that moves value). From then on, an out-of-scope payment is impossible: the check runs before the money-moving code, so even a fully compromised model can't execute it. Every allowed action emits a signed, tamper-proof receipt — a clean audit trail, and evidence if a charge is ever disputed.

Install

npm install @vantic/sdk

Protect your agent in ~5 lines

import { generateKeyPair, issueMandate, AgentWallet } from "@vantic/sdk";

const owner = generateKeyPair();   // you (the principal)
const agent = generateKeyPair();   // your autonomous agent

// Authorize the agent: what it may pay for, ≤ $200 each, ≤ $500/week, only these counterparties.
const mandate = issueMandate({
  agent: agent.publicKey,
  principal: owner.publicKey,
  principalPrivateKeyPem: owner.privateKeyPem,
  ttlSeconds: 7 * 24 * 3600,
  scope: {
    budget: { currency: "USD", amount: 50000, windowSeconds: 7 * 24 * 3600 }, // $500 / 7 days
    maxPerTransaction: 20000,                                                  // $200
    allowedActions: ["purchase", "subscribe"], // any money-moving action: transfer, payout, refund, …
    allowedCounterparties: ["etsy.com", "*.shop.example"],
  },
});

const wallet = new AgentWallet(mandate, agent.privateKeyPem);

// Your real payment call goes inside the executor. The guard runs FIRST;
// if the action is out of scope, the executor is never called.
await wallet.spend(
  { type: "purchase", counterparty: "etsy.com", amount: 4500, currency: "USD" },
  async (action) => ({ outcome: "settled", result: await pay(action) }),
);

/

Run npm run guard-demo to watch it block live attacker payments.

Already have a payment tool? Wrap it once.

For MCP / LangChain / function-calling agents, gate an existing tool without restructuring anything:

import { wrapMcpTool } from "@vantic/sdk";

const guardedPurchase = wrapMcpTool(purchaseTool, {
  wallet,
  toAction: (args) => ({ type: "purchase", counterparty: args.merchant, amount: args.amountCents, currency: args.currency }),
});
// Register `guardedPurchase` instead of `purchaseTool`. A blocked call comes back as a tool
// error the model can read and recover from; the real charge never fires.

Framework guides (OpenAI, LangChain, Vercel AI SDK, MCP, raw): docs/integrations.md.

What you get

Shortened. The full README is on GitHub.