Model Context Protocol (MCP)

Client                           Snack Money API
  |                                    |
  |-------- tools/call -------->      |
  |        (no payment)               |
  |                                    |
  |<------ Error -32402 --------      |
  |     (payment required)            |
  |                                    |
  |-- Sign with x402 client -->       |
  |                                    |
  |-------- tools/call -------->      |
  |     (with payment proof)          |
  |                                    |
  |<-------- Success ----------       |
  |      (with receipt)               |

const response = await fetch('https://api.snack.money/mcp', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    jsonrpc: '2.0',
    method: 'initialize',
    params: {
      protocolVersion: '0.1.0',
      clientInfo: { name: 'my-agent', version: '1.0.0' }
    },
    id: 1
  })
});

const response = await fetch('https://api.snack.money/mcp', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    jsonrpc: '2.0',
    method: 'tools/list',
    id: 2
  })
});

const { result } = await response.json();
console.log('Available tools:', result.tools);

import { X402 } from '@x402/core';
import { createEvmClient } from '@x402/evm';

// Initialize x402 client
const x402Client = createEvmClient({
  privateKey: process.env.EVM_PRIVATE_KEY,
  chainId: 8453 // Base mainnet
});

// First call - will require payment
const firstCall = await fetch('https://api.snack.money/mcp', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({
    jsonrpc: '2.0',
    method: 'tools/call',
    params: {
      name: 'pay_twitter',
      arguments: {
        receiver: 'alice',
        amount: 0.01,
        description: 'Thanks for the help!'
      }
    },
    id: 3
  })
});

const response = await firstCall.json();

// Check if payment is required
if (response.error?.code === -32402) {
  const { taskId, paymentRequired } = response.error.data;

  // Sign payment
  const signedPayment = await x402Client.createPaymentPayload(
    paymentRequired
  );

  // Retry with payment
  const paidCall = await fetch('https://api.snack.money/mcp', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
      jsonrpc: '2.0',
      method: 'tools/call',
      params: {
        name: 'pay_twitter',
        arguments: {
          receiver: 'alice',
          amount: 0.01,
          description: 'Thanks for the help!'
        },
        _meta: {
          taskId,
          x402Payment: signedPayment
        }
      },
      id: 4
    })
  });

  const result = await paidCall.json();
  console.log('Payment successful:', result.result);
}