diff --git a/src/utils.rs b/src/utils.rs
index e927443..d20796a 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -1,11 +1,13 @@
 //! Shared utility functions.
 
-/// Create a safe folder name from person name or ID.
+/// Create a safe snake_case folder name from person name or ID.
 ///
 /// This sanitizes user input to create safe filesystem paths by:
 /// - Using the person name if provided and non-empty, otherwise falling back to ID
+/// - Converting to lowercase
+/// - Replacing spaces with underscores
 /// - Replacing unsafe characters with underscores
-/// - Trimming whitespace
+/// - Trimming whitespace and underscores
 /// - Limiting length to 50 characters
 ///
 /// Note: The frontend has a JavaScript version of this function that must be
@@ -13,11 +15,12 @@
 pub fn sanitize_folder_name(name: Option<&str>, id: &str) -> String {
     let base = name.filter(|n| !n.is_empty()).unwrap_or(id);
 
-    // Replace unsafe characters with underscores
+    // Convert to lowercase and replace unsafe characters with underscores
     let sanitized: String = base
+        .to_lowercase()
         .chars()
         .map(|c| {
-            if c.is_alphanumeric() || c == '-' || c == '_' || c == ' ' {
+            if c.is_alphanumeric() || c == '-' || c == '_' {
                 c
             } else {
                 '_'
@@ -25,8 +28,8 @@ pub fn sanitize_folder_name(name: Option<&str>, id: &str) -> String {
         })
         .collect();
 
-    // Trim whitespace and limit length
-    let trimmed = sanitized.trim();
+    // Trim whitespace/underscores and limit length
+    let trimmed = sanitized.trim_matches(|c: char| c.is_whitespace() || c == '_');
     if trimmed.len() > 50 {
         trimmed[..50].to_string()
     } else {
@@ -40,7 +43,7 @@ mod tests {
 
     #[test]
     fn test_sanitize_folder_name_with_name() {
-        assert_eq!(sanitize_folder_name(Some("John Doe"), "abc123"), "John Doe");
+        assert_eq!(sanitize_folder_name(Some("John Doe"), "abc123"), "john_doe");
     }
 
     #[test]
@@ -53,7 +56,7 @@ mod tests {
     fn test_sanitize_folder_name_replaces_unsafe_chars() {
         assert_eq!(
             sanitize_folder_name(Some("John/Doe:Test"), "id"),
-            "John_Doe_Test"
+            "john_doe_test"
         );
     }
 
@@ -61,7 +64,7 @@ mod tests {
     fn test_sanitize_folder_name_trims_whitespace() {
         assert_eq!(
             sanitize_folder_name(Some("  John Doe  "), "id"),
-            "John Doe"
+            "john_doe"
         );
     }