MCP Server with x402

# Clone the x402 repository
git clone https://github.com/x402-foundation/x402.git
cd x402/examples/typescript

# Install dependencies and build packages
pnpm install && pnpm build

# Navigate to the MCP client example
cd clients/mcp

{
  "mcpServers": {
    "demo": {
      "command": "pnpm",
      "args": [
        "--silent",
        "-C",
        "<absolute path to this repo>/examples/typescript/clients/mcp",
        "dev"
      ],
      "env": {
        "EVM_PRIVATE_KEY": "<private key of a wallet with USDC on Base Sepolia>",
        "SVM_PRIVATE_KEY": "<base58-encoded private key of a Solana wallet with USDC on Devnet>",
        "RESOURCE_SERVER_URL": "http://localhost:4021",
        "ENDPOINT_PATH": "/weather"
      }
    }
  }
}

# In another terminal, from the examples/typescript directory
cd servers/express
pnpm dev

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import axios from "axios";
import { x402Client, wrapAxiosWithPayment } from "@x402/axios";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { registerExactSvmScheme } from "@x402/svm/exact/client";
import { privateKeyToAccount } from "viem/accounts";
import { createKeyPairSignerFromBytes } from "@solana/kit";
import { base58 } from "@scure/base";
import { config } from "dotenv";

config();

const evmPrivateKey = process.env.EVM_PRIVATE_KEY as `0x${string}`;
const svmPrivateKey = process.env.SVM_PRIVATE_KEY as string;
const baseURL = process.env.RESOURCE_SERVER_URL || "http://localhost:4021";
const endpointPath = process.env.ENDPOINT_PATH || "/weather";

if (!evmPrivateKey && !svmPrivateKey) {
  throw new Error("At least one of EVM_PRIVATE_KEY or SVM_PRIVATE_KEY must be provided");
}

/**
 * Creates an axios client configured with x402 payment support for EVM and/or SVM.
 */
async function createClient() {
  const client = new x402Client();

  // Register EVM scheme if private key is provided
  if (evmPrivateKey) {
    const evmSigner = privateKeyToAccount(evmPrivateKey);
    registerExactEvmScheme(client, { signer: evmSigner });
  }

  // Register SVM scheme if private key is provided
  if (svmPrivateKey) {
    const svmSigner = await createKeyPairSignerFromBytes(base58.decode(svmPrivateKey));
    registerExactSvmScheme(client, { signer: svmSigner });
  }

  return wrapAxiosWithPayment(axios.create({ baseURL }), client);
}

async function main() {
  const api = await createClient();

  // Create an MCP server
  const server = new McpServer({
    name: "x402 MCP Client Demo",
    version: "2.0.0",
  });

  // Add a tool that calls the paid API
  server.tool(
    "get-data-from-resource-server",
    "Get data from the resource server (in this example, the weather)",
    {},
    async () => {
      const res = await api.get(endpointPath);
      return {
        content: [{ type: "text", text: JSON.stringify(res.data) }],
      };
    },
  );

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

main().catch(error => {
  console.error(error);
  process.exit(1);
});

import { x402Client, wrapAxiosWithPayment } from "@x402/axios";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { registerExactSvmScheme } from "@x402/svm/exact/client";

const client = new x402Client();

// Register EVM scheme for Base/Ethereum payments
registerExactEvmScheme(client, { signer: evmSigner });

// Register SVM scheme for Solana payments
registerExactSvmScheme(client, { signer: svmSigner });

// Now handles both EVM and Solana networks automatically
const httpClient = wrapAxiosWithPayment(axios.create({ baseURL }), client);

HTTP/1.1 402 Payment Required
PAYMENT-REQUIRED: <base64-encoded JSON>

{
  "content": [
    {
      "type": "text",
      "text": "{\"report\":{\"weather\":\"sunny\",\"temperature\":70}}"
    }
  ]
}

{
  "dependencies": {
    "@modelcontextprotocol/sdk": "^1.9.0",
    "@x402/axios": "workspace:*",
    "@x402/evm": "workspace:*",
    "@x402/svm": "workspace:*",
    "axios": "^1.13.2",
    "viem": "^2.39.0",
    "@solana/kit": "^2.1.1",
    "@scure/base": "^1.2.6"
  }
}

┌─────────────────┐     ┌─────────────────┐     ┌─────────────────┐
│  Claude Desktop │────▶│   MCP Server    │────▶│  x402 API       │
│                 │     │  (x402 client)  │     │  (paid endpoint)│
└─────────────────┘     └─────────────────┘     └─────────────────┘
        │                       │                       │
        │  1. Call tool         │  2. GET /weather      │
        │                       │                       │
        │                       │  3. 402 + requirements│
        │                       │◀──────────────────────│
        │                       │                       │
        │                       │  4. Sign payment      │
        │                       │                       │
        │                       │  5. Retry with payment│
        │                       │──────────────────────▶│
        │                       │                       │
        │                       │  6. 200 + data        │
        │                       │◀──────────────────────│
        │                       │                       │
        │  7. Return response   │                       │
        │◀──────────────────────│                       │

CDP_API_KEY_ID=your-api-key-id
CDP_API_KEY_SECRET=your-api-key-secret
CDP_WALLET_SECRET=your-wallet-secret
RESOURCE_SERVER_URL=http://localhost:4021
ENDPOINT_PATH=/weather

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import axios from "axios";
import { CdpX402Client } from "@coinbase/cdp-sdk/x402";
import { wrapAxiosWithPayment } from "@x402/axios";
import { config } from "dotenv";

config();

const baseURL = process.env.RESOURCE_SERVER_URL as string;
const endpointPath = process.env.ENDPOINT_PATH as string;

if (!baseURL || !endpointPath) {
  throw new Error("Missing environment variables");
}

// CdpX402Client provisions and signs with a CDP-managed wallet (reads CDP_* from env).
// It registers exact + upto on the environment's Base network (Base mainnet by default;
// pass environment: "development" for Base Sepolia), replacing the manual scheme setup
// above. Add Solana or other networks via networkSchemes — see the CDP SDK concept page.
const client = new CdpX402Client();

// Print the wallet address so you know which one to fund with USDC.
const { evmAddress } = await client.getAddresses();
console.error("Fund this EVM address with USDC:", evmAddress);

const api = wrapAxiosWithPayment(axios.create({ baseURL }), client);

const server = new McpServer({
  name: "x402 MCP Client Demo",
  version: "1.0.0",
});

server.tool(
  "get-data-from-resource-server",
  "Get data from the resource server (in this example, the weather)",
  {},
  async () => {
    const res = await api.get(endpointPath);
    return {
      content: [{ type: "text", text: JSON.stringify(res.data) }],
    };
  },
);

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