Simple MCP Server

Instructions

Implementation Reference

• src/index.ts:342-372 (handler)

  The core handler function for the 'write_file' tool. Validates the filepath using PathValidator, checks file extension, creates parent directory if necessary, writes content using fs.promises.writeFile, and returns a success CallToolResult.

  private async writeFile(filepath: string, content: string): Promise<CallToolResult> {
    try {
      const pathValidation = this.pathValidator.validatePath(filepath);
      if (!pathValidation.isValid) {
        throw new Error(pathValidation.error);
      }
  
      const extValidation = this.pathValidator.validateFileExtension(pathValidation.normalizedPath);
      if (!extValidation.isValid) {
        throw new Error(extValidation.error);
      }
  
      console.error(`Writing file: ${pathValidation.normalizedPath}`);
      // ディレクトリが存在しない場合は作成
      const dir = path.dirname(pathValidation.normalizedPath);
      await fs.mkdir(dir, { recursive: true });
  
      await fs.writeFile(pathValidation.normalizedPath, content, "utf-8");
      return {
        content: [
          {
            type: "text",
            text: `ファイル "${pathValidation.normalizedPath}" に正常に書き込みました`,
          },
        ],
        isError: false,
      };
    } catch (error) {
      throw new Error(`ファイルの書き込みに失敗: ${error}`);
    }
  }

• src/index.ts:129-146 (registration)

  Registration of the 'write_file' tool in the TOOLS constant array. Includes the tool name, description, and inputSchema for parameter validation (filepath: string, content: string). This is returned by ListToolsRequest.

  {
    name: "write_file",
    description: "指定されたファイルにテキストを書き込みます（許可されたディレクトリのみ）",
    inputSchema: {
      type: "object",
      properties: {
        filepath: {
          type: "string",
          description: "書き込むファイルのパス",
        },
        content: {
          type: "string",
          description: "書き込む内容",
        },
      },
      required: ["filepath", "content"],
    },
  },

• src/index.ts:278-282 (handler)

  The dispatch case in the CallToolRequest handler switch statement that routes 'write_file' calls to the writeFile method, extracting filepath and content from arguments.

  case "write_file":
    return await this.writeFile(
      args.filepath as string,
      args.content as string
    );

• src/index.ts:132-145 (schema)

  The inputSchema definition for the 'write_file' tool, specifying required string parameters filepath and content with descriptions.

  inputSchema: {
    type: "object",
    properties: {
      filepath: {
        type: "string",
        description: "書き込むファイルのパス",
      },
      content: {
        type: "string",
        description: "書き込む内容",
      },
    },
    required: ["filepath", "content"],
  },