Add clamp_height to the markdown filter which limits max height to 200 (scrollable) on the container div

netbox/project-static/styles/custom/_markdown.scss

@@ -35,6 +35,11 @@ td > .rendered-markdown {
   }
 }
 
+td > .rendered-markdown.vertical-scroll {
+  max-height: 200px;
+  overflow-y: scroll;
+}
+
 // Markdown preview
 .markdown-widget {
   .preview {

netbox/utilities/templates/builtins/customfield_value.html

@@ -3,7 +3,7 @@
 {% if customfield.type == 'integer' and value is not None %}
   {{ value }}
 {% elif customfield.type == 'longtext' and value %}
-  {{ value|markdown }}
+  {{ value|markdown:True }}
 {% elif customfield.type == 'boolean' and value == True %}
   {% checkmark value true="True" %}
 {% elif customfield.type == 'boolean' and value == False %}

netbox/utilities/templatetags/builtins/filters.py

@@ -159,11 +159,16 @@ def content_type_id(model):
 #
 
 @register.filter('markdown', is_safe=True)
-def render_markdown(value):
+def render_markdown(value, clamp_height=False):
     """
     Render a string as Markdown. This filter is invoked as "markdown":
 
         {{ md_source_text|markdown }}
+
+    If clamp_height is True, the "vertical-scroll" class will be added to the container div which sets a max-height
+    and adds a vertical scrollbar:
+
+        {{ md_source_text|markdown:True }}
     """
     if not value:
         return ''
@@ -178,7 +183,11 @@ def render_markdown(value):
 
     # If the string is not empty wrap it in rendered-markdown to style tables
     if html:
-        html = f'<div class="rendered-markdown">{html}</div>'
+        classes = ['rendered-markdown']
+        if clamp_height:
+            classes.append('vertical-scroll')
+        classes_str = ' '.join(classes)
+        html = f'<div class="{classes_str}">{html}</div>'
 
     schemes = get_config().ALLOWED_URL_SCHEMES