MCP-Pay

An HTTP x402 monetization layer on Algorand that lets AI agents pay for MCP tools on a sub-cent, pay-per-call basis.

Problem

Autonomous AI agents using the Model Context Protocol (MCP) cannot access paid tools: credit cards, API keys, and subscriptions are human workflows. Tool creators have no way to charge per call, and legacy chains are too slow or expensive for machine-to-machine micropayments.

Related MCP server: Loop MCP DualRail

Solution

MCP-Pay converts any MCP tool into an instantly monetized x402 endpoint on Algorand.

1. An agent discovers tools at GET /mcp/v1/tools (free, includes JSON schemas + prices).

2. The agent invokes POST /mcp/v1/tools/:name/execute without payment.

3. The server answers 402 Payment Required with payment metadata (price in USDC, receiver address, network).

4. The agent's local middleware auto-signs an Algorand USDC transfer (ASA 31566704) and retries.

5. The GoPlausible facilitator verifies and settles on-chain (<3.3s finality), the tool executes, and results return in one round-trip.

No accounts. No keys. No humans.

USP

Paid Tools Included

Architecture

┌────────────────────────┐
│   AI AGENT (client/)   │  1. GET /mcp/v1/tools      (discovery)
│  auto-paying MCP agent │  2. POST .../execute       → 402 challenge
└───────────┬────────────┘  3. sign USDC txn locally
            │               4. retry + X-PAYMENT header
            ▼
┌────────────────────────┐
│  MCP-PAY SERVER (Hono) │  x402 paymentMiddleware protects each tool route
│  registry + tools/*    │  executes tool only after verified settlement
└───────────┬────────────┘
            ▼
┌────────────────────────┐
│ GOPLAUSIBLE FACILITATOR│  /verify + /settle on Algorand TestNet
│  https://facilitator.  │  USDC (ASA 31566704) transfer
│  goplausible.xyz       │
└────────────────────────┘

Tech Stack

• TypeScript, Hono

• @x402/core, @x402/avm, @x402/hono, @x402/fetch

• @x402-avm/extensions (Bazaar discovery)

• GoPlausible facilitator, Algorand TestNet USDC

Run Locally

1. Prerequisites

• Node.js 18+, pnpm (npm i -g pnpm)

• Two funded Algorand TestNet accounts:

  • Server wallet (receiver): address only

  • Agent wallet (payer): mnemonic, kept local — never committed

Fund via Lora faucet, opt both into USDC in Lora, then get TestNet USDC from the Circle faucet (choose Algorand Testnet).

2. Configure

pnpm install
cp .env.example .env

Fill .env:

AVM_ADDRESS=<server wallet address>          # receiver
AVM_MNEMONIC="<agent 25-word mnemonic>"      # payer, LOCAL ONLY
SERVER_URL=http://localhost:4021

3. Start server + run agent

pnpm server        # terminal 1
pnpm agent         # terminal 2: discovery → 402 → auto-pay → result

Verify On-Chain

Every successful call settles a real TestNet transaction:

• Facilitator dashboard: https://facilitator.goplausible.xyz/dashboard

• Lora explorer: https://lora.algokit.io/testnet

Example settlement TX (from demo run):

TODO: paste Lora transaction link after first live run

API

Roadmap

• Spend-policy guard: per-agent budgets enforced by the middleware

• Creator dashboard: register your own MCP tool + price in minutes

• Bazaar listing at GoPlausible so any third-party agent can discover MCP-Pay tools