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.

Screenshots

(All six captures live in docs/.)

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.

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

Typical paid API	MCP-Pay
One hardcoded endpoint	Tool registry: any tool becomes a priced service with a schema
Docs written for humans	Agent-native discovery: agents list, compare, and select tools programmatically
Subscriptions / prepaid credits	True pay-per-call settled on-chain per request
EVM gas kills micropayments	Algorand: ~0.001 ALGO fee, 3.3s finality

Paid Tools Included

Tool	What it does	Price
web_research	Reader-mode extraction of any public web page for LLM context	$0.002
market_data	Live crypto spot prices from a keyless public feed	$0.001
contract_audit	Static heuristic security scan of Solidity source	$0.005

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

Live Deployment

Production server running on Railway:

https://mcp-pay-production.up.railway.app

Try it: GET /health or browse GET /mcp/v1/tools — then pay with any x402 client.

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

Verified settlements from actual demo runs:

Tool	Price	Transaction
web_research	$0.002	PNSX3OTXTMP5V7JEDDWD2G3H7KS3R7NTB2DO4RFXNR3URYUCPPPQ
market_data	$0.001	E4OFWPYIXJNGWRYMAJIA2EZOBAQXZ7HI4UOBOFRZPLLNGPAKMZKA
contract_audit	$0.005	settled (see facilitator dashboard)
market_data (production)	$0.001	DUITAVSQ3TU7WNHMQSNGHXBHG6MFEIBNYJY5HAYC2NNZVG5244YQ

API

Endpoint	Payment	Description
GET /health	free	liveness
GET /mcp/v1/tools	free	tool catalog with schemas + prices
POST /mcp/v1/tools/:name/execute	x402	execute a tool, pay-per-call

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