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How to build an MCP server that can interact with Monad Testnet

In this guide, you will learn how to build a Model Context Protocol (MCP) server that allows an MCP Client (Claude Desktop) to query Monad Testnet to check the MON balance of an account.

What is MCP?​

The Model Context Protocol (MCP) is a standard that allows AI models to interact with external tools and services.

Prerequisites​

  • Node.js (v16 or later)
  • npm or yarn
  • Claude Desktop

Getting started​

  1. Clone the monad-mcp-tutorial repository. This repository has some code that can help you get started quickly.
git clone https://github.com/monad-developers/monad-mcp-tutorial.git
  1. Install dependencies:
npm install

Building the MCP server​

Monad Testnet-related configuration is already added to index.ts in the src folder.

Define the server instance​

// Create a new MCP server instance
const server = new McpServer({
  name: "monad-mcp-tutorial",
  version: "0.0.1",
  // Array of supported tool names that clients can call
  capabilities: ["get-mon-balance"]
});

Define the MON balance tool​

Below is the scaffold of the get-mon-balance tool:

server.tool(
    // Tool ID 
    "get-mon-balance",
    // Description of what the tool does
    "Get MON balance for an address on Monad testnet",
    // Input schema
    {
        address: z.string().describe("Monad testnet address to check balance for"),
    },
    // Tool implementation
    async ({ address }) => {
        // code to check MON balance
    }
);

Let's add the MON balance check implementation to the tool:

server.tool(
    // Tool ID 
    "get-mon-balance",
    // Description of what the tool does
    "Get MON balance for an address on Monad testnet",
    // Input schema
    {
        address: z.string().describe("Monad testnet address to check balance for"),
    },
    // Tool implementation
    async ({ address }) => {
        try {
            // Check MON balance for the input address
            const balance = await publicClient.getBalance({
                address: address as `0x${string}`,
            });

            // Return a human friendly message indicating the balance.
            return {
                content: [
                    {
                        type: "text",
                        text: `Balance for ${address}: ${formatUnits(balance, 18)} MON`,
                    },
                ],
            };
        } catch (error) {
            // If the balance check process fails, return a graceful message back to the MCP client indicating a failure.
            return {
                content: [
                    {
                        type: "text",
                        text: `Failed to retrieve balance for address: ${address}. Error: ${
                        error instanceof Error ? error.message : String(error)
                        }`,
                    },
                ],
            };
        }
    }
);

Initialize the transport and server from the main function​

async function main() {
    // Create a transport layer using standard input/output
    const transport = new StdioServerTransport();
    
    // Connect the server to the transport
    await server.connect(transport);
}

Build the project​

npm run build

The server is now ready to use!

Add the MCP server to Claude Desktop​

  1. Open "Claude Desktop"

claude desktop

  1. Open Settings

Claude > Settings > Developer

claude settings

  1. Open claude_desktop_config.json

claude config

  1. Add details about the MCP server and save the file.
{
  "mcpServers": {
    ...
    "monad-mcp": {
      "command": "node",
      "args": [
        "/<path-to-project>/build/index.js"
      ]
    }
  }
}
  1. Restart "Claude Desktop"

Use the MCP server​

You should now be able to see the tools in Claude!

tools

Here's the final result

final result

Further resources​