diff --git a/src/application/dtos/file_dto.rs b/src/application/dtos/file_dto.rs
index 2f05e6fb..18cc815a 100644
--- a/src/application/dtos/file_dto.rs
+++ b/src/application/dtos/file_dto.rs
@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 use crate::domain::entities::file::File;
 use serde::{Deserialize, Serialize};
 
@@ -20,8 +22,9 @@ pub struct FileDto {
     /// Size in bytes
     pub size: u64,
 
-    /// MIME type
-    pub mime_type: String,
+    /// MIME type — `Arc<str>` because MIME values repeat across files
+    /// and DTOs are cloned on every request (clone is O(1) atomic increment).
+    pub mime_type: Arc<str>,
 
     /// Parent folder ID
     pub folder_id: Option<String>,
@@ -32,15 +35,15 @@ pub struct FileDto {
     /// Last modification timestamp
     pub modified_at: u64,
 
-    // ── Pre-computed display fields ──
+    // ── Pre-computed display fields (Arc<str>: values come from static tables) ──
     /// FontAwesome icon CSS class (e.g. "fas fa-file-image")
-    pub icon_class: String,
+    pub icon_class: Arc<str>,
 
     /// Extra CSS class for icon styling (e.g. "image-icon", "" when default)
-    pub icon_special_class: String,
+    pub icon_special_class: Arc<str>,
 
     /// Human-readable file category (e.g. "Image", "Document")
-    pub category: String,
+    pub category: Arc<str>,
 
     /// Human-readable formatted size (e.g. "3.27 MB")
     pub size_formatted: String,
@@ -61,13 +64,13 @@ impl From<File> for FileDto {
             name: name.to_string(),
             path: file.path_string().to_string(),
             size,
-            mime_type: mime.to_string(),
+            mime_type: Arc::from(mime),
             folder_id: file.folder_id().map(String::from),
             created_at: file.created_at(),
             modified_at: file.modified_at(),
-            icon_class: icon_class_for(name, mime).to_string(),
-            icon_special_class: icon_special_class_for(name, mime).to_string(),
-            category: category_for(name, mime).to_string(),
+            icon_class: Arc::from(icon_class_for(name, mime)),
+            icon_special_class: Arc::from(icon_special_class_for(name, mime)),
+            category: Arc::from(category_for(name, mime)),
             size_formatted: format_file_size(size),
             owner_id: file.owner_id().map(String::from),
         }
@@ -84,7 +87,7 @@ impl From<FileDto> for File {
             dto.name,
             dto.path,
             dto.size,
-            dto.mime_type,
+            dto.mime_type.to_string(),
             dto.folder_id,
             dto.created_at,
             dto.modified_at,
@@ -100,13 +103,13 @@ impl FileDto {
             name: "stub-file".to_string(),
             path: "/stub/path".to_string(),
             size: 0,
-            mime_type: "application/octet-stream".to_string(),
+            mime_type: Arc::from("application/octet-stream"),
             folder_id: None,
             created_at: 0,
             modified_at: 0,
-            icon_class: "fas fa-file".to_string(),
-            icon_special_class: String::new(),
-            category: "Document".to_string(),
+            icon_class: Arc::from("fas fa-file"),
+            icon_special_class: Arc::from(""),
+            category: Arc::from("Document"),
             size_formatted: "0 Bytes".to_string(),
             owner_id: None,
         }
diff --git a/src/application/dtos/folder_dto.rs b/src/application/dtos/folder_dto.rs
index 2c6466d8..32e7ce4e 100644
--- a/src/application/dtos/folder_dto.rs
+++ b/src/application/dtos/folder_dto.rs
@@ -1,3 +1,5 @@
+use std::sync::Arc;
+
 use crate::domain::entities::folder::Folder;
 use serde::{Deserialize, Serialize};
 
@@ -53,15 +55,15 @@ pub struct FolderDto {
     /// Whether this is a root folder
     pub is_root: bool,
 
-    // ── Pre-computed display fields ──
+    // ── Pre-computed display fields (Arc<str>: always identical values) ──
     /// FontAwesome icon CSS class (always "fas fa-folder")
-    pub icon_class: String,
+    pub icon_class: Arc<str>,
 
     /// Extra CSS class for icon styling (always "folder-icon")
-    pub icon_special_class: String,
+    pub icon_special_class: Arc<str>,
 
     /// Human-readable category (always "Folder")
-    pub category: String,
+    pub category: Arc<str>,
 }
 
 impl From<Folder> for FolderDto {
@@ -77,9 +79,9 @@ impl From<Folder> for FolderDto {
             created_at: folder.created_at(),
             modified_at: folder.modified_at(),
             is_root,
-            icon_class: "fas fa-folder".to_string(),
-            icon_special_class: "folder-icon".to_string(),
-            category: "Folder".to_string(),
+            icon_class: Arc::from("fas fa-folder"),
+            icon_special_class: Arc::from("folder-icon"),
+            category: Arc::from("Folder"),
         }
     }
 }
@@ -112,9 +114,9 @@ impl FolderDto {
             created_at: 0,
             modified_at: 0,
             is_root: true,
-            icon_class: "fas fa-folder".to_string(),
-            icon_special_class: "folder-icon".to_string(),
-            category: "Folder".to_string(),
+            icon_class: Arc::from("fas fa-folder"),
+            icon_special_class: Arc::from("folder-icon"),
+            category: Arc::from("Folder"),
         }
     }
 }
diff --git a/src/application/ports/file_ports.rs b/src/application/ports/file_ports.rs
index ba791c55..bbb497bf 100644
--- a/src/application/ports/file_ports.rs
+++ b/src/application/ports/file_ports.rs
@@ -93,7 +93,7 @@ pub enum OptimizedFileContent {
     /// Small-file content (possibly transcoded / compressed) already in RAM.
     Bytes {
         data: Bytes,
-        mime_type: String,
+        mime_type: Arc<str>,
         was_transcoded: bool,
     },
     /// Memory-mapped file (10–100 MB).
diff --git a/src/application/services/file_retrieval_service.rs b/src/application/services/file_retrieval_service.rs
index 83666078..fdf8c05f 100644
--- a/src/application/services/file_retrieval_service.rs
+++ b/src/application/services/file_retrieval_service.rs
@@ -61,7 +61,7 @@ impl FileRetrievalService {
         mime: &str,
         file_size: u64,
         accept_webp: bool,
-    ) -> Option<(Bytes, String)> {
+    ) -> Option<(Bytes, Arc<str>)> {
         if !accept_webp {
             return None;
         }
@@ -81,7 +81,7 @@ impl FileRetrievalService {
                     transcoded.len(),
                     (1.0 - transcoded.len() as f64 / content.len().max(1) as f64) * 100.0
                 );
-                Some((transcoded, webp_mime))
+                Some((transcoded, Arc::from(&*webp_mime)))
             }
             _ => None,
         }
@@ -152,7 +152,7 @@ impl FileRetrievalService {
             // Store in cache
             if let Some(cache) = &self.content_cache {
                 let etag: Arc<str> = format!("\"{}-{}\"", id, modified_at).into();
-                let ct: Arc<str> = Arc::from(&*mime_type);
+                let ct: Arc<str> = mime_type.clone();
                 cache
                     .put(id.to_string(), content_bytes.clone(), etag, ct)
                     .await;
diff --git a/src/application/services/search_service.rs b/src/application/services/search_service.rs
index c0e9a9d7..efc987e6 100644
--- a/src/application/services/search_service.rs
+++ b/src/application/services/search_service.rs
@@ -158,7 +158,7 @@ impl SearchService {
             name: file.name.clone(),
             path: file.path.clone(),
             size: file.size,
-            mime_type: file.mime_type.clone(),
+            mime_type: file.mime_type.to_string(),
             folder_id: file.folder_id.clone(),
             created_at: file.created_at,
             modified_at: file.modified_at,
diff --git a/src/common/stubs.rs b/src/common/stubs.rs
index 5b0b8485..2b849b6c 100644
--- a/src/common/stubs.rs
+++ b/src/common/stubs.rs
@@ -505,7 +505,7 @@ impl FileRetrievalUseCase for StubFileRetrievalUseCase {
             FileDto::default(),
             OptimizedFileContent::Bytes {
                 data: Bytes::new(),
-                mime_type: String::new(),
+                mime_type: Arc::from(""),
                 was_transcoded: false,
             },
         ))
diff --git a/src/infrastructure/services/path_resolver_service.rs b/src/infrastructure/services/path_resolver_service.rs
index d7f81896..ed54e2b2 100644
--- a/src/infrastructure/services/path_resolver_service.rs
+++ b/src/infrastructure/services/path_resolver_service.rs
@@ -149,9 +149,9 @@ impl PathResolverService {
                 created_at: created_at as u64,
                 modified_at: modified_at as u64,
                 is_root: false,
-                icon_class: "fas fa-folder".to_string(),
-                icon_special_class: "folder-icon".to_string(),
-                category: "Folder".to_string(),
+                icon_class: Arc::from("fas fa-folder"),
+                icon_special_class: Arc::from("folder-icon"),
+                category: Arc::from("Folder"),
             })),
             _ => {
                 let mime = mime_type.unwrap_or_else(|| "application/octet-stream".to_string());
@@ -161,13 +161,13 @@ impl PathResolverService {
                     name: name.clone(),
                     path: res_path,
                     size: sz,
-                    mime_type: mime.clone(),
+                    mime_type: Arc::from(&*mime),
                     folder_id,
                     created_at: created_at as u64,
                     modified_at: modified_at as u64,
-                    icon_class: icon_class_for(&name, &mime).to_string(),
-                    icon_special_class: icon_special_class_for(&name, &mime).to_string(),
-                    category: category_for(&name, &mime).to_string(),
+                    icon_class: Arc::from(icon_class_for(&name, &mime)),
+                    icon_special_class: Arc::from(icon_special_class_for(&name, &mime)),
+                    category: Arc::from(category_for(&name, &mime)),
                     size_formatted: format_file_size(sz),
                     owner_id: user_id,
                 }))
diff --git a/src/interfaces/api/handlers/file_handler.rs b/src/interfaces/api/handlers/file_handler.rs
index 26c95a28..9152c352 100644
--- a/src/interfaces/api/handlers/file_handler.rs
+++ b/src/interfaces/api/handlers/file_handler.rs
@@ -433,7 +433,7 @@ impl FileHandler {
                         Ok(stream) => {
                             return Response::builder()
                                 .status(StatusCode::PARTIAL_CONTENT)
-                                .header(header::CONTENT_TYPE, &file_dto.mime_type)
+                                .header(header::CONTENT_TYPE, &*file_dto.mime_type)
                                 .header(header::CONTENT_DISPOSITION, &disposition)
                                 .header(header::CONTENT_LENGTH, range_length)
                                 .header(
@@ -488,7 +488,7 @@ impl FileHandler {
                     .into_response(),
                 OptimizedFileContent::Mmap(mmap_data) => Response::builder()
                     .status(StatusCode::OK)
-                    .header(header::CONTENT_TYPE, &file_dto.mime_type)
+                    .header(header::CONTENT_TYPE, &*file_dto.mime_type)
                     .header(header::CONTENT_DISPOSITION, &disposition)
                     .header(header::CONTENT_LENGTH, mmap_data.len())
                     .header(header::ETAG, &etag)
@@ -502,7 +502,7 @@ impl FileHandler {
                     .into_response(),
                 OptimizedFileContent::Stream(pinned_stream) => Response::builder()
                     .status(StatusCode::OK)
-                    .header(header::CONTENT_TYPE, &file_dto.mime_type)
+                    .header(header::CONTENT_TYPE, &*file_dto.mime_type)
                     .header(header::CONTENT_DISPOSITION, &disposition)
                     .header(header::CONTENT_LENGTH, file_dto.size)
                     .header(header::ETAG, &etag)
diff --git a/src/interfaces/api/handlers/webdav_handler.rs b/src/interfaces/api/handlers/webdav_handler.rs
index 0c13212e..6e8ad4b2 100644
--- a/src/interfaces/api/handlers/webdav_handler.rs
+++ b/src/interfaces/api/handlers/webdav_handler.rs
@@ -286,9 +286,9 @@ async fn handle_propfind(
             created_at: Utc::now().timestamp() as u64,
             modified_at: Utc::now().timestamp() as u64,
             is_root: true,
-            icon_class: "fas fa-folder".to_string(),
-            icon_special_class: "folder-icon".to_string(),
-            category: "Folder".to_string(),
+            icon_class: Arc::from("fas fa-folder"),
+            icon_special_class: Arc::from("folder-icon"),
+            category: Arc::from("Folder"),
         };
 
         return build_streaming_propfind_response(
@@ -609,7 +609,7 @@ async fn handle_get(
     // Build streaming response using Content-Length from metadata
     Ok(Response::builder()
         .status(StatusCode::OK)
-        .header(header::CONTENT_TYPE, file.mime_type)
+        .header(header::CONTENT_TYPE, &*file.mime_type)
         .header(header::CONTENT_LENGTH, file.size)
         .header(header::ETAG, format!("\"{}\"", file.id))
         .header(
@@ -658,7 +658,7 @@ async fn handle_head(
             Ok(ResolvedResource::File(file)) => {
                 return Ok(Response::builder()
                     .status(StatusCode::OK)
-                    .header(header::CONTENT_TYPE, &file.mime_type)
+                    .header(header::CONTENT_TYPE, &*file.mime_type)
                     .header(header::CONTENT_LENGTH, file.size)
                     .header(header::ETAG, format!("\"{}\"", file.id))
                     .header(
@@ -693,7 +693,7 @@ async fn handle_head(
 
     Ok(Response::builder()
         .status(StatusCode::OK)
-        .header(header::CONTENT_TYPE, &file.mime_type)
+        .header(header::CONTENT_TYPE, &*file.mime_type)
         .header(header::CONTENT_LENGTH, file.size)
         .header(header::ETAG, format!("\"{}\"", file.id))
         .header(