MetaMask MCP

Instructions

Implementation Reference

• src/tools/send-transaction.ts:21-55 (handler)

  Handler function that executes the send-transaction tool by calling wagmi's sendTransaction, returning the transaction hash or error message.

  execute: async (args) => {
    try {
      const result = await sendTransaction(wagmiConfig, args);
      return {
        content: [
          {
            type: "text",
            text: JSONStringify({
              hash: result,
            }),
          },
        ],
      };
    }
    catch (error) {
      if (error instanceof TransactionExecutionError) {
        return {
          content: [
            {
              type: "text",
              text: error.cause.message,
            },
          ],
        };
      }
      return {
        content: [
          {
            type: "text",
            text: (error as Error).message,
          },
        ],
      };
    }
  },

• src/tools/send-transaction.ts:13-20 (schema)

  Zod schema defining the input parameters for the send-transaction tool.

  parameters: z.object({
    to: Address.describe("The transaction recipient or contract address."),
    data: Address.optional().describe("A contract hashed method call with encoded args."),
    value: z.coerce.bigint().optional().describe("Value in wei sent with this transaction."),
    maxFeePerGas: z.coerce.bigint().optional().describe("Total fee per gas in wei, inclusive of maxPriorityFeePerGas."),
    maxPriorityFeePerGas: z.coerce.bigint().optional().describe("Max priority fee per gas in wei."),
    chainId: z.coerce.number().optional().describe("Chain ID to validate against before sending transaction."),
  }),

• src/tools/send-transaction.ts:9-57 (registration)

  Function that registers the send-transaction tool with FastMCP server, defining name, description, schema, and handler.

  export function registerSendTransactionTools(server: FastMCP, wagmiConfig: Config): void {
    server.addTool({
      name: "send-transaction",
      description: "Send transactions to networks.",
      parameters: z.object({
        to: Address.describe("The transaction recipient or contract address."),
        data: Address.optional().describe("A contract hashed method call with encoded args."),
        value: z.coerce.bigint().optional().describe("Value in wei sent with this transaction."),
        maxFeePerGas: z.coerce.bigint().optional().describe("Total fee per gas in wei, inclusive of maxPriorityFeePerGas."),
        maxPriorityFeePerGas: z.coerce.bigint().optional().describe("Max priority fee per gas in wei."),
        chainId: z.coerce.number().optional().describe("Chain ID to validate against before sending transaction."),
      }),
      execute: async (args) => {
        try {
          const result = await sendTransaction(wagmiConfig, args);
          return {
            content: [
              {
                type: "text",
                text: JSONStringify({
                  hash: result,
                }),
              },
            ],
          };
        }
        catch (error) {
          if (error instanceof TransactionExecutionError) {
            return {
              content: [
                {
                  type: "text",
                  text: error.cause.message,
                },
              ],
            };
          }
          return {
            content: [
              {
                type: "text",
                text: (error as Error).message,
              },
            ],
          };
        }
      },
    });
  };

• src/tools/register-tools.ts:52-52 (registration)

  Call to register the send-transaction tool as part of the central tools registration.

  registerSendTransactionTools(server, wagmiConfig);

• src/index.ts:15-15 (registration)

  Top-level call to register all tools, including send-transaction.

  registerTools(server, wagmiConfig);