Command Executor MCP Server

Instructions

Implementation Reference

• src/index.ts:89-128 (handler)

  Handler for CallToolRequestSchema that checks for 'execute_command', validates the command against allowed list, executes it using child_process.exec (promisified), and returns text content with stdout/stderr or error message.

  this.server.setRequestHandler(CallToolRequestSchema, async (request) => {
    if (request.params.name !== 'execute_command') {
      throw new McpError(
        ErrorCode.MethodNotFound,
        `Unknown tool: ${request.params.name}`
      );
    }
  
    const { command } = request.params.arguments as { command: string };
  
    // コマンドが許可されているか確認
    if (!this.isCommandAllowed(command)) {
      throw new McpError(
        ErrorCode.InvalidParams,
        `Command not allowed: ${command}. Allowed commands: ${this.allowedCommands.join(', ')}`
      );
    }
  
    try {
      const { stdout, stderr } = await execAsync(command);
      return {
        content: [
          {
            type: 'text',
            text: stdout || stderr,
          },
        ],
      };
    } catch (error: any) {
      return {
        content: [
          {
            type: 'text',
            text: `Command execution failed: ${error.message}`,
          },
        ],
        isError: true,
      };
    }
  });

• src/index.ts:75-84 (schema)

  Input schema definition for the execute_command tool, specifying a required 'command' string property.

  inputSchema: {
    type: 'object',
    properties: {
      command: {
        type: 'string',
        description: '実行するコマンド',
      },
    },
    required: ['command'],
  },

• src/index.ts:70-87 (registration)

  Tool registration in the ListToolsRequestSchema handler, defining the name, description, and input schema for 'execute_command'.

  this.server.setRequestHandler(ListToolsRequestSchema, async () => ({
    tools: [
      {
        name: 'execute_command',
        description: '事前に許可されたコマンドを実行します',
        inputSchema: {
          type: 'object',
          properties: {
            command: {
              type: 'string',
              description: '実行するコマンド',
            },
          },
          required: ['command'],
        },
      },
    ],
  }));

• src/index.ts:63-67 (helper)

  Helper function to check if a command prefix matches the list of allowed commands.

  private isCommandAllowed(command: string): boolean {
    // コマンドの最初の部分（スペース区切りの最初の単語）を取得
    const commandPrefix = command.split(' ')[0];
    return this.allowedCommands.some(allowed => commandPrefix === allowed);
  }

• src/index.ts:26-32 (helper)

  Helper function to retrieve the list of allowed commands from environment variable or defaults.

  const getAllowedCommands = (): string[] => {
    const envCommands = process.env.ALLOWED_COMMANDS;
    if (!envCommands) {
      return DEFAULT_ALLOWED_COMMANDS;
    }
    return envCommands.split(',').map(cmd => cmd.trim());
  };