MCPilot

Instructions

Implementation Reference

• packages/metamask-mcp/src/tools/write-contract.ts:18-60 (handler)

  Handler function that executes the write-contract tool: parses ABI, calls wagmi's writeContract, returns transaction hash or error message.

  execute: async (_args) => {
    try {
      const abi = JSON.parse(_args.abi) as Abi
      const address = _args.abi as Address
      const functionName = _args.functionName
      const args = _args.args
      const result = await writeContract(wagmiConfig, {
        abi,
        address,
        functionName,
        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,
          }
        ]
      }
    }
  },

• packages/metamask-mcp/src/tools/write-contract.ts:12-17 (schema)

  Zod schema defining the input parameters for the write-contract tool: abi (string), address (string), functionName (string), args (array of strings).

  parameters: z.object({
    abi: z.string(),
    address: z.string(),
    functionName: z.string(),
    args: z.string().array()
  }),

• packages/metamask-mcp/src/tools/write-contract.ts:8-62 (registration)

  Function that registers the write-contract tool on the FastMCP server, including name, description, schema, and handler.

  export function registerWriteContractTools(server: FastMCP): void {
    server.addTool({
      name: "write-contract",
      description: "Execute a write function on a contract",
      parameters: z.object({
        abi: z.string(),
        address: z.string(),
        functionName: z.string(),
        args: z.string().array()
      }),
      execute: async (_args) => {
        try {
          const abi = JSON.parse(_args.abi) as Abi
          const address = _args.abi as Address
          const functionName = _args.functionName
          const args = _args.args
          const result = await writeContract(wagmiConfig, {
            abi,
            address,
            functionName,
            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,
              }
            ]
          }
        }
      },
    });
  };

• packages/metamask-mcp/src/index.ts:61-61 (registration)

  Invocation of the registration function in the main server setup file, adding the tool to the MetaMask MCP server.

  registerWriteContractTools(server);