diff --git a/Repository/Extension/StringExtensions.cs b/Repository/Extension/StringExtensions.cs
new file mode 100644
index 0000000..bf607bb
--- /dev/null
+++ b/Repository/Extension/StringExtensions.cs
@@ -0,0 +1,57 @@
+using System;
+using System.Text.RegularExpressions;
+
+namespace Repository.Extension
+{
+    public static class StringExtensions
+    {
+        /// <summary>
+        /// 原字符轉換Niagara特殊字符
+        /// </summary>
+        /// <param name="input">原始字串</param>
+        /// <returns>轉換後的字串</returns>
+        public static string ConvertN4(this string input)
+        {
+            if (string.IsNullOrEmpty(input)) return input;
+
+            // 數字開頭加上 "$3"
+            if (Regex.IsMatch(input, @"^\d"))
+            {
+                input = "$3" + input;
+            }
+
+            // 包含 "-" 轉換為 "$2d"
+            if (input.Contains("-"))
+            {
+                input = input.Replace("-", "$2d");
+            }
+
+            return input;
+        }
+        /// <summary>
+        /// Niagara特殊字符轉換原字符
+        /// </summary>
+        /// <param name="input">原始字串</param>
+        /// <returns>轉換後的字串</returns>
+        public static string ConvertNormal(this string input)
+        {
+            if (string.IsNullOrEmpty(input)) return input;
+
+            // 包含"$2d" 轉換回 "-"
+            if (input.Contains("$2d"))
+            {
+                input = input.Replace("$2d", "-");
+            }
+
+            // "$3" 開頭移除 "$3"
+            if (input.StartsWith("$3"))
+            {
+                input = input.Substring(2); // 移除前兩個字元
+            }
+
+            return input;
+        }
+
+    }
+
+}