AgentPay — agentpay.help

Machine-payable AI microservices via the 402 Payment Required protocol (x402 / MPP)

No accounts. No API keys. No OAuth. Pay per call in USDC on Base.

AgentPay is an open-source reference implementation of the Machine Payments Protocol — wrapping local AI models behind an HTTP 402 paywall so that AI agents (and humans) can pay for compute on a per-request basis using stablecoins.

Built with Express 5, @x402/express, and Ollama-served Gemma models. Live on Base mainnet with the PayAI facilitator.

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Table of Contents

• Quick Start
• Architecture
• Services & Pricing
• Tech Stack
• Deployment
• API Reference
• Configuration
• Contributing
• License

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Quick Start

Prerequisites

• Node.js ≥ 20
• Ollama running locally with the required model pulled
• A wallet private key (for receiving payments)

1. Clone & install

git clone https://github.com/your-org/AgentPay.git
cd AgentPay
npm install

2. Pull the AI model

ollama pull gemma3:1b
# Or use a larger model for better quality:
# ollama pull gemma4:31b-cloud

3. Configure

cp .env.example .env
# Edit .env — set SELLER_ADDRESS to your wallet address

4. Start the server

npm start
# AgentPay listening on :4021
#   payTo:   0xYourWalletAddress
#   network: eip155:84532 (Base Sepolia testnet)
#   facilitator: https://x402.org/facilitator

5. Test a paid request

# Unpaid request → HTTP 402 (paywall)
curl -s -o /dev/null -w "%{http_code}" -X POST https://agentpay.help/v1/summarize \
  -H 'Content-Type: application/json' \
  -d '{"text":"Machine Payments Protocol lets AI agents pay for API calls using the HTTP 402 status code."}'
# → 402

# Automated test (requires buyer wallet with USDC)
npm run test:402

6. Buy a service (buyer client)

# Set your buyer private key in .env
echo "BUYER_PK=0xYourPrivateKey" >> .env

# Run the buyer script
npm run buyer -- /v1/summarize ./payload.json

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Architecture

┌─────────────────────────────────────────────────────────────────┐
│                        AgentPay Architecture                   │
├─────────────────────────────────────────────────────────────────┤
│                                                                 │
│  ┌──────────┐    HTTP POST     ┌───────────────────────────┐    │
│  │  Client   │ ──────────────► │      Express 5 Server     │    │
│  │ (Agent /  │   (no auth)     │        (port 4021)        │    │
│  │  Human)   │                 │                           │    │
│  └──────────┘                 │  ┌─────────────────────┐  │    │
│       │                       │  │   Payment Middleware  │  │    │
│       │                       │  │   (@x402/express)    │  │    │
│       │                       │  │                      │  │    │
│       │  ◄── HTTP 402 ───────│  │  • Validates x402    │  │    │
│       │      (paywall)        │  │    payment headers   │  │    │
│       │                       │  │  • Verifies on-chain │  │    │
│       │  ──── signed payment ►│  │    via facilitator   │  │    │
│       │      (USDC)           │  │                      │  │    │
│       │                       │  └──────────┬──────────┘  │    │
│       │  ◄── 200 OK ─────────│             │              │    │
│       │      (result JSON)    │  ┌──────────▼──────────┐  │    │
│       │                       │  │   Service Handlers   │  │    │
│       │                       │  │                      │  │    │
│       │                       │  │  /v1/summarize       │  │    │
│       │                       │  │  /v1/classify-ins    │  │    │
│       │                       │  │  /v1/extract         │  │    │
│       │                       │  └──────────┬──────────┘  │    │
│       │                       └─────────────┼─────────────┘    │
│       │                                     │                   │
│       │                              ┌──────▼──────┐           │
│       │                              │   Ollama     │           │
│       │                              │  (local LLM) │           │
│       │                              │  gemma3:1b   │           │
│       │                              └─────────────┘           │
│       │                                                         │
│  ┌────▼────────────────────────────────────────────────────┐    │
│  │                  Payment Flow (x402)                    │    │
│  │                                                         │    │
│  │  Client ──► HTTP 402 ──► Facilitator ──► On-Chain ──►   │    │
│  │                │         (PayAI)       Base Mainnet     │    │
│  │                ▼                         (USDC)         │    │
│  │          Payment Required                                │    │
│  │          (price + accepts[])                             │    │
│  └─────────────────────────────────────────────────────────┘    │
│                                                                 │
│  ┌─────────────────────────────────────────────────────────┐    │
│  │  Free Endpoints (no paywall)                            │    │
│  │  • /              — Landing page (HTML)                 │    │
│  │  • /health        — Health check                        │    │
│  │  • /stats         — Revenue & usage stats               │    │
│  │  • /.well-known/x402 — Machine-readable service catalog │    │
│  └─────────────────────────────────────────────────────────┘    │
│                                                                 │
│  ┌─────────────────────────────────────────────────────────┐    │
│  │  Data Layer                                             │    │
│  │  • data/ledger.json — Append-only payment ledger        │    │
│  └─────────────────────────────────────────────────────────┘    │
└─────────────────────────────────────────────────────────────────┘

How it works:

1. Client sends POST /v1/summarize (or any paid endpoint) — no auth headers needed
2. Payment middleware intercepts, returns HTTP 402 with pricing info (accepts[])
3. Client constructs a USDC payment, signs it, attaches X-PAYMENT header
4. Facilitator verifies the payment on Base mainnet
5. Middleware grants access → request proceeds to the service handler
6. Handler calls Ollama, returns AI-generated result as JSON

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Services & Pricing

All services accept USDC on Base mainnet (chain ID 8453) via the exact payment scheme. Testnet (Base Sepolia) is available via configuration.

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Tech Stack

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Deployment

Local Development

# Base Sepolia testnet (recommended for development)
cp .env.example .env
# Edit .env: PAYMENT_NETWORK=eip155:84532
npm start

Production (Base Mainnet)

# Edit .env for mainnet
PAYMENT_NETWORK=eip155:8453       # Base mainnet
SELLER_ADDRESS=0xYourMainnetWallet
OLLAMA_URL=http://127.0.0.1:11434
MODEL_SUMMARIZE=gemma4:31b-cloud  # Use larger model for quality
MODEL_CLASSIFY=gemma4:31b-cloud
MODEL_EXTRACT=gemma4:31b-cloud

Docker (recommended for production)

FROM node:20-slim
WORKDIR /app
COPY package*.json ./
RUN npm ci --omit=dev
COPY src/ ./src/
COPY data/ ./data/
EXPOSE 4021
HEALTHCHECK CMD curl -f https://agentpay.help/health || exit 1
CMD ["node", "src/server.js"]

Environment Variables

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API Reference

Free Endpoints

GET /

Landing page with service catalog and usage stats.

GET /health

Health check.

{ "ok": true, "ts": "2025-01-01T00:00:00.000Z" }

GET /stats

Revenue and usage statistics.

{
  "requests_paid": 42,
  "gross_usd": 0.84,
  "by_service": { "summarize": 0.42, "classify-insurance": 0.28, "extract": 0.14 },
  "last_20": [...]
}

GET /.well-known/x402

Machine-readable service catalog (Bazaar discovery extension). Use this for automated service discovery by AI agents.

{
  "name": "AgentPay",
  "description": "Pay-per-call AI microservices (x402 / MPP)",
  "endpoints": [
    { "path": "/v1/summarize", "method": "POST", "price": "$0.01", "description": "Summarize text (200-20k chars)" },
    { "path": "/v1/classify-insurance", "method": "POST", "price": "$0.02", "description": "Insurance lead classification" },
    { "path": "/v1/extract", "method": "POST", "price": "$0.03", "description": "Structured field extraction" }
  ]
}

---

Paid Endpoints

All paid endpoints require a valid x402 payment in the X-PAYMENT header. Unpaid requests receive HTTP 402 Payment Required.

POST /v1/summarize — $0.01

Summarize text into a concise ~250-word output.

Request:

{
  "text": "Your text to summarize (200-20000 characters)..."
}

Response (200 OK):

{
  "summary": "The text discusses...",
  "words": 247
}

Errors:

• 400 — Missing text field or text exceeds 20,000 characters
• 402 — Payment required (see x402 protocol)
• 502 — Upstream AI model failed

---

POST /v1/classify-insurance — $0.02

Classify an insurance lead or customer message.

Request:

{
  "text": "I was in a car accident last week and need to file a claim urgently..."
}

Response (200 OK):

{
  "intent": "claim",
  "urgency": "high",
  "line": "auto",
  "confidence": 0.92
}

Possible values:

• intent: quote_request | renewal | claim | complaint | other
• urgency: low | medium | high
• line: auto | home | life | health | commercial | other

---

POST /v1/extract — $0.03

Extract structured fields from raw text (emails, forms, documents).

Request:

{
  "text": "From: john@example.com\nSubject: Policy #12345 renewal\nDear customer, your auto policy expires on March 15...",
  "fields": ["email", "policy_number", "expiry_date"]
}

Response (200 OK):

{
  "email": "john@example.com",
  "policy_number": "12345",
  "expiry_date": "March 15"
}

If fields is omitted, all extractable key-value pairs are returned.

---

Client Library (Buyer)

Use @x402/fetch to automatically handle the 402 → payment → retry flow:

import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { ExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const signer = privateKeyToAccount(process.env.BUYER_PK);
const client = x402Client.fromConfig({
  schemes: [{ network: "eip155:*", client: new ExactEvmScheme(signer) }],
});

const payFetch = wrapFetchWithPayment(globalThis.fetch, client);

// This automatically handles the 402 → payment → retry flow
const res = await payFetch("https://agentpay.help/v1/summarize", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ text: "Your text here..." }),
});

const result = await res.json();
console.log(result.summary);

---

Contributing

Contributions are welcome! This is an open-source reference implementation of the x402 / MPP protocol.

Development Setup

git clone https://github.com/your-org/AgentPay.git
cd AgentPay
npm install
cp .env.example .env
# Edit .env with your test wallet and Base Sepolia settings
npm start

Adding a New Service

1. Define the payment middleware entry in src/server.js under the paymentMiddleware() call
2. Add the route handler after the middleware block
3. Register the endpoint in /.well-known/x402 discovery
4. Add to the landing page HTML

Guidelines

• Keep it simple. This is a reference implementation — clarity over complexity.
• Test on Base Sepolia first. Use the testnet before going to mainnet.
• Use @x402/ packages. Don't reinvent payment verification.
• Append-only ledger. Never modify data/ledger.json — only append.

Reporting Issues

Open a GitHub issue with:

• Steps to reproduce
• Expected vs. actual behavior
• Environment (Node version, OS, model used)

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License

MIT

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Resources

• x402 Protocol Spec — The Machine Payments Protocol
• PayAI Facilitator — Payment verification service
• Base Network — OP Stack L2 where USDC payments settle
• Ollama — Local LLM inference engine
• viem — TypeScript Ethereum client