diff --git a/cmd_addtag.go b/cmd_addtag.go
new file mode 100644
index 0000000..14c48ad
--- /dev/null
+++ b/cmd_addtag.go
@@ -0,0 +1,148 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"unicode"
+)
+
+// AddTag generates code for a new custom tag
+func AddTag(delimiter, tagName, targetElement string) {
+	fmt.Printf("Adding tag: %s -> %s (delimiter: %s)\n", tagName, targetElement, delimiter)
+
+	if err := updateTagsFile(delimiter, tagName); err != nil {
+		fmt.Printf("Error updating templates/tags.go: %v\n", err)
+		os.Exit(1)
+	}
+
+	if err := updateParseFile(tagName, targetElement); err != nil {
+		fmt.Printf("Error updating parse.go: %v\n", err)
+		os.Exit(1)
+	}
+
+	fmt.Println("Successfully added tag!")
+}
+
+func updateTagsFile(delimiter, tagName string) error {
+	path := "templates/tags.go"
+	content, err := os.ReadFile(path)
+	if err != nil {
+		return err
+	}
+
+	pascalTagName := toPascalCase(tagName)
+	newLine := fmt.Sprintf("var %s = customtag.New(\"%s\", \"%s\")\n", pascalTagName, delimiter, tagName)
+
+	// check if already exists
+	if strings.Contains(string(content), newLine) {
+		fmt.Println("Tag definition already exists in templates/tags.go")
+		return nil
+	}
+
+	// Append to file
+	f, err := os.OpenFile(path, os.O_APPEND|os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if _, err := f.WriteString(newLine); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func updateParseFile(tagName, targetElement string) error {
+	path := "parse.go"
+	contentBytes, err := os.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	content := string(contentBytes)
+
+	pascalTagName := toPascalCase(tagName)
+
+	// 1. Add to Goldmark Extensions
+	// Find `templates.SidebarTag,` or `templates.TopBanner,` and add after it
+	// We'll look for `goldmark.WithExtensions(` and find the closing `),`
+	
+	extLine := fmt.Sprintf("\t\t\t\ttemplates.%s,", pascalTagName)
+	if !strings.Contains(content, extLine) {
+		// Simple insertion strategy: find `templates.TopBanner,`
+		anchor := "templates.TopBanner,"
+		if idx := strings.Index(content, anchor); idx != -1 {
+			insertAt := idx + len(anchor)
+			content = content[:insertAt] + "\n" + extLine + content[insertAt:]
+		} else {
+			return fmt.Errorf("could not find anchor 'templates.TopBanner,' in parse.go to insert extension registration")
+		}
+	} else {
+		fmt.Println("Extension registration already exists in parse.go")
+	}
+
+	// 2. Add Post-Processing Logic
+	// We'll look for `// Build Full Page` and insert before it, or after the TopBanner block.
+	// A good anchor is `// _-_- TopBanner` block's end. 
+
+	// Let's construct the code block to insert
+	targetTag, targetClass := parseTargetElement(targetElement)
+	
+	// Prepare the replacement logic
+	var replacementLogic string
+	if targetClass != "" {
+		replacementLogic = fmt.Sprintf(`return fmt.Sprintf("<%s class=\"%s\">%%s</%s>", innerContent)`, targetTag, targetClass, targetTag)
+	} else {
+		replacementLogic = fmt.Sprintf(`return fmt.Sprintf("<%s>%%s</%s>", innerContent)`, targetTag, targetTag)
+	}
+
+	codeBlock := fmt.Sprintf(`
+			// %s %s
+			%sRegex := regexp.MustCompile("(?s)<%s>.*?</%s>")
+			if %sRegex.MatchString(htmlContent) {
+				htmlContent = %sRegex.ReplaceAllStringFunc(htmlContent, func(match string) string {
+					innerContent := strings.TrimPrefix(match, "<%s>")
+					innerContent = strings.TrimSuffix(innerContent, "</%s>")
+					%s
+				})
+			}
+`, pascalTagName, tagName, tagName, tagName, tagName, tagName, tagName, tagName, tagName, replacementLogic)
+
+	if !strings.Contains(content, fmt.Sprintf("%sRegex :=", tagName)) {
+		// Anchor: find end of TopBanner block
+		// We know TopBanner block ends with a closing brace for the `if topbannerRegex.MatchString` block
+		// But strictly speaking, we are inside `if file.RoutePath == "/" { ... }`.
+		// Let's look for `// Build Full Page` and insert BEFORE it.
+		
+		
+		anchor := "// Build Full Page"
+		if idx := strings.Index(content, anchor); idx != -1 {
+			// Insert BEFORE "// Build Full Page", which matches the global scope (after the if block)
+			content = content[:idx] + codeBlock + content[idx:]
+		} else {
+			return fmt.Errorf("could not find anchor '// Build Full Page' in parse.go")
+		}
+	} else {
+		fmt.Println("Regex logic already exists in parse.go")
+	}
+
+	return os.WriteFile(path, []byte(content), 0644)
+}
+
+func toPascalCase(s string) string {
+	if s == "" {
+		return ""
+	}
+	runes := []rune(s)
+	runes[0] = unicode.ToUpper(runes[0])
+	return string(runes)
+}
+
+func parseTargetElement(t string) (string, string) {
+	parts := strings.Split(t, ".")
+	if len(parts) == 2 {
+		return parts[0], parts[1]
+	}
+	return t, ""
+}
diff --git a/content/entries/entry1.md b/content/entries/entry1.md
index 930f533..297cee4 100644
--- a/content/entries/entry1.md
+++ b/content/entries/entry1.md
@@ -1 +1,7 @@
-# I'm quite fond of lyrics. Particicularly, I like interpol lyrics.
\ No newline at end of file
+# I'm quite fond of lyrics. Particicularly, I like interpol lyrics.
+
+I'm testing custom tags:
+
+{[]}(\(x+x\)).
+
+{[]}x+1 
diff --git a/main.go b/main.go
index ba56832..259c9b8 100644
--- a/main.go
+++ b/main.go
@@ -19,6 +19,14 @@ func main() {
 			ClearCache()
 			StartServer()
 			return
+		case "addTag":
+			if len(os.Args) < 5 {
+				fmt.Println("Usage: blog addTag {delimiter} {tagName} {targetElement}")
+				fmt.Println("Example: blog addTag {[]} mathtext li.mathtext")
+				return
+			}
+			AddTag(os.Args[2], os.Args[3], os.Args[4])
+			return
 		default:
 			fmt.Printf("Unknown command: %s\nUsage: blog [service|test]\n", os.Args[1])
 			return
diff --git a/parse.go b/parse.go
index 0ca004a..d9694f3 100644
--- a/parse.go
+++ b/parse.go
@@ -61,6 +61,7 @@ func GetContentPath(file ContentFile) (string, error) {
 				&frontmatter.Extender{},
 				templates.SidebarTag, // ||| -> <sidebar>
 				templates.TopBanner,
+				templates.Mathtext,
 			),
 			goldmark.WithRendererOptions(
 				html.WithUnsafe(),
@@ -143,9 +144,21 @@ func GetContentPath(file ContentFile) (string, error) {
 					return fmt.Sprintf(`<div class="topbanner">%s</div>`, bannerHTML)
 				})
 			}
-		}
+		
 
-		// Build Full Page
+}
+
+		
+			// Mathtext mathtext
+			mathtextRegex := regexp.MustCompile("(?s)<mathtext>.*?</mathtext>")
+			if mathtextRegex.MatchString(htmlContent) {
+				htmlContent = mathtextRegex.ReplaceAllStringFunc(htmlContent, func(match string) string {
+					innerContent := strings.TrimPrefix(match, "<mathtext>")
+					innerContent = strings.TrimSuffix(innerContent, "</mathtext>")
+					return fmt.Sprintf("<li class=\"mathtext\">%s</li>", innerContent)
+				})
+			}
+// Build Full Page
 		dataToWrite = templates.BuildFullPage([]byte(htmlContent), meta)
 	}
 
diff --git a/templates/tags.go b/templates/tags.go
index 6abd385..cd10b3b 100644
--- a/templates/tags.go
+++ b/templates/tags.go
@@ -6,3 +6,4 @@ import customtag "github.com/tendstofortytwo/goldmark-customtag"
 // ||| -> <sidebar></sidebar>
 var SidebarTag = customtag.New("|||", "sidebar")
 var TopBanner = customtag.New("_-_-", "topbanner")
+var Mathtext = customtag.New("{[]}", "mathtext")