Ethereum RPC MCP Server

Instructions

Implementation Reference

• index.js:172-193 (handler)

  The handler function that performs the eth_getBalance RPC call via makeRpcCall, converts the balance from wei to ETH, and returns a formatted text response.

  async (args) => {
    try {
      console.error(`Getting balance for address: ${args.address} at block: ${args.blockParameter}`);
      
      const balance = await makeRpcCall('eth_getBalance', [args.address, args.blockParameter]);
      // Convert hex balance to decimal and then to ETH for readability
      const balanceWei = parseInt(balance, 16);
      const balanceEth = balanceWei / 1e18;
      
      return {
        content: [{ 
          type: "text", 
          text: `Balance for ${args.address}:\n${balanceWei} Wei\n${balanceEth.toFixed(6)} ETH` 
        }]
      };
    } catch (error) {
      return {
        content: [{ type: "text", text: `Error: Failed to get balance. ${error.message}` }],
        isError: true
      };
    }
  }

• index.js:168-171 (schema)

  Zod input schema defining the parameters for the eth_getBalance tool: address (required, Ethereum address format) and blockParameter (optional, defaults to 'latest').

  {
    address: z.string().regex(/^0x[a-fA-F0-9]{40}$/).describe('The Ethereum address to check balance'),
    blockParameter: z.string().default('latest').describe('Block parameter (default: "latest")')
  },

• index.js:165-194 (registration)

  MCP server.tool registration for the eth_getBalance tool, including name, description, input schema, and handler function.

  server.tool(
    'eth_getBalance',
    'Retrieves the balance of a given Ethereum address',
    {
      address: z.string().regex(/^0x[a-fA-F0-9]{40}$/).describe('The Ethereum address to check balance'),
      blockParameter: z.string().default('latest').describe('Block parameter (default: "latest")')
    },
    async (args) => {
      try {
        console.error(`Getting balance for address: ${args.address} at block: ${args.blockParameter}`);
        
        const balance = await makeRpcCall('eth_getBalance', [args.address, args.blockParameter]);
        // Convert hex balance to decimal and then to ETH for readability
        const balanceWei = parseInt(balance, 16);
        const balanceEth = balanceWei / 1e18;
        
        return {
          content: [{ 
            type: "text", 
            text: `Balance for ${args.address}:\n${balanceWei} Wei\n${balanceEth.toFixed(6)} ETH` 
          }]
        };
      } catch (error) {
        return {
          content: [{ type: "text", text: `Error: Failed to get balance. ${error.message}` }],
          isError: true
        };
      }
    }
  );

• index.js:84-102 (helper)

  Helper function used by eth_getBalance (and other tools) to make POST requests to the Ethereum RPC endpoint and handle responses/errors.

  async function makeRpcCall(method, params = []) {
    try {
      const response = await axios.post(ETH_RPC_URL, {
        jsonrpc: '2.0',
        id: 1,
        method,
        params
      });
  
      if (response.data.error) {
        throw new Error(`RPC Error: ${response.data.error.message}`);
      }
  
      return response.data.result;
    } catch (error) {
      console.error(`Error making RPC call to ${method}:`, error.message);
      throw error;
    }
  }