Payflow SDK

The Payflow SDK is a Typescript library for building paid MCP servers using various micropayment protocols. It extends the Model Context Protocol SDK to provide a unified interface for building paid MCP servers.

Features

• [x] Easy interface to register paid tools
• [x] Support for x402 payment schema with USDC on Base
• [ ] Support for x402 with other assets and networks
• [ ] Extensible payment processing (like with Agent Commerce Kit, Stripe, etc.)

Installation

npm install @chainbound/payflow-sdk
# or
pnpm add @chainbound/payflow-sdk
# or
yarn add @chainbound/payflow-sdk

Quick Start

1. Basic Setup

import { PayflowMcpServer } from '@chainbound/payflow-sdk';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import { z } from 'zod';

// Create a server
const server = new PayflowMcpServer({
  name: 'my-paid-server',
  version: '1.0.0',
}, {
  x402: {
    version: 1,
    keyId: process.env.CDP_API_KEY_ID,
    keySecret: process.env.CDP_API_KEY_SECRET,
  }
});

// Connect transport
const transport = new StdioServerTransport();
await server.connect(transport);

2. Register a Paid Tool

// Simple paid tool without parameters
server.paidTool(
  'hello_world',
  'Says hello to the world',
  {
    price: 0.01,           // Price in USDC
    recipient: '0x1234...' // Ethereum address to receive payment
  },
  async () => {
    return {
      content: [{ 
        type: 'text', 
        text: 'Hello, World!' 
      }]
    };
  }
);

3. Paid Tool with Parameters

server.paidTool(
  'generate_text',
  'Generates custom text based on input',
  {
    price: 0.05,
    recipient: '0x1234...'
  },
  {
    prompt: z.string().describe('The text prompt to generate from'),
    length: z.number().max(1000).describe('Maximum length of generated text')
  },
  async ({ prompt, length }) => {
    // Your tool logic here
    const generatedText = await someAIService.generate(prompt, length);
    
    return {
      content: [{ 
        type: 'text', 
        text: generatedText 
      }]
    };
  }
);

API Reference

PayflowMcpServer

Extends the standard McpServer with paid tool capabilities.

const server = new PayflowMcpServer(serverInfo, options?);

paidTool()

Register a tool that requires payment before execution.

Signatures:

// Basic paid tool
paidTool(name: string, options: PaymentOptions, callback: ToolCallback)

// With description
paidTool(name: string, description: string, options: PaymentOptions, callback: ToolCallback)

// With parameters schema
paidTool<Args>(name: string, options: PaymentOptions, paramsSchema: Args, callback: ToolCallback<Args>)

// With description and parameters
paidTool<Args>(name: string, description: string, options: PaymentOptions, paramsSchema: Args, callback: ToolCallback<Args>)

// With annotations
paidTool<Args>(name: string, description: string, options: PaymentOptions, paramsSchema: Args, annotations: ToolAnnotations, callback: ToolCallback<Args>)

PaymentOptions

Configuration for payment requirements:

type PaymentOptions = {
  price: number;        // Price in USDC
  recipient: string;    // Ethereum address to receive payment
  asset?: string;       // Asset address (optional, defaults to USDC)
  network?: number | string; // Network (optional, defaults to Base)
}

How Payments Work

1. Client Request: Client calls your paid tool with a payment parameter containing an x402 payment header
2. Payment Verification: SDK automatically verifies the payment against your specified requirements
3. Tool Execution: If payment is valid, your tool callback is executed
4. Payment Settlement: Payment is settled on-chain
5. Response: Tool result is returned with payment transaction reference

sequenceDiagram
    participant Client
    participant PayflowServer as Payflow MCP Server
    participant Facilitator as x402 Facilitator
    participant Blockchain as Base Network
    participant ToolLogic as Your Tool Logic

    Client->>PayflowServer: Call paid tool with payment header
    
    Note over PayflowServer: Step 1: Payment Verification
    PayflowServer->>PayflowServer: Decode x402 payment
    PayflowServer->>PayflowServer: Generate payment requirements
    PayflowServer->>Facilitator: Verify payment against requirements
    Facilitator-->>PayflowServer: Payment verification result
    
    alt Payment Invalid
        PayflowServer-->>Client: Error: Invalid payment
    else Payment Valid
        Note over PayflowServer: Step 2: Tool Execution
        PayflowServer->>ToolLogic: Execute tool callback with params
        ToolLogic-->>PayflowServer: Tool execution result
        
        Note over PayflowServer: Step 3: Payment Settlement
        PayflowServer->>Facilitator: Settle payment on-chain
        Facilitator->>Blockchain: Submit payment transaction
        Blockchain-->>Facilitator: Transaction hash
        Facilitator-->>PayflowServer: Settlement response
        
        Note over PayflowServer: Step 4: Response
        PayflowServer->>PayflowServer: Add transaction reference to result
        PayflowServer-->>Client: Tool result + payment transaction
    end

Complete Example

import { PayflowMcpServer } from '@chainbound/payflow-sdk';
import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
import { z } from 'zod';

const server = new PayflowMcpServer({
  name: 'weather-server',
  version: '1.0.0',
});

// Free tool (standard MCP)
server.tool(
  'get_weather_info',
  'Get general weather information',
  async () => ({
    content: [{ 
      type: 'text', 
      text: 'Weather service available. Use get_weather for specific locations.' 
    }]
  })
);

// Paid tool for detailed weather
server.paidTool(
  'get_weather',
  'Get detailed weather for a specific location',
  {
    price: 0.02,
    recipient: '0x742d35Cc6634C0532925a3b8D1d3e14C1C3E6FC8' // Your wallet address
  },
  {
    location: z.string().describe('City name or coordinates'),
    units: z.enum(['metric', 'imperial']).optional().describe('Temperature units')
  },
  async ({ location, units = 'metric' }) => {
    // Call your weather API
    const weather = await weatherAPI.getWeather(location, units);
    
    return {
      content: [{ 
        type: 'text', 
        text: `Weather in ${location}: ${weather.temperature}°${units === 'metric' ? 'C' : 'F'}, ${weather.condition}` 
      }]
    };
  }
);

// Start server
const transport = new StdioServerTransport();
await server.connect(transport);

Environment Setup

Your MCP server should handle these environment variables:

CDP_API_KEY_ID=your-api-key-id
CDP_API_KEY_SECRET=your-api-key-secret

Client Usage

Clients need to provide payment headers when calling paid tools. The payment header should be generated using the x402 protocol with your specified price and recipient.

License

MIT