diff --git a/app/task/[id].tsx b/app/task/[id].tsx
index 245900c..a540f1a 100644
--- a/app/task/[id].tsx
+++ b/app/task/[id].tsx
@@ -54,6 +54,7 @@ type TaskData = {
   priority: number;
   dueDate: Date | null;
   listId: string;
+  parentId: string | null;
   recurrence: string | null;
 };
 
@@ -400,67 +401,71 @@ export default function TaskDetailScreen() {
           </>
         )}
 
-        {/* Subtasks */}
-        <Text className={`mb-2 mt-6 text-xs uppercase tracking-wide ${isDark ? 'text-[#A0A0A0]' : 'text-[#6B6B6B]'}`} style={{ fontFamily: 'Inter_600SemiBold' }}>
-          {t('task.subtasks')}
-        </Text>
-        {subtasks.map((sub) => (
-          <Pressable
-            key={sub.id}
-            onPress={() => editingSubtaskId === sub.id ? undefined : handleToggleSubtask(sub.id)}
-            onLongPress={() => handleEditSubtask(sub)}
-            className={`flex-row items-center border-b py-2.5 ${isDark ? 'border-[#3A3A3A]' : 'border-[#E5E7EB]'}`}
-          >
-            <View
-              className="mr-3 h-5 w-5 items-center justify-center rounded-full border-2"
-              style={{
-                borderColor: sub.completed ? colors.bleu.DEFAULT : colors.priority.none,
-                backgroundColor: sub.completed ? colors.bleu.DEFAULT : 'transparent',
-              }}
-            >
-              {sub.completed && <Text className="text-xs text-white" style={{ fontFamily: 'Inter_700Bold' }}>✓</Text>}
-            </View>
-            {editingSubtaskId === sub.id ? (
+        {/* Subtasks — only for root tasks (not subtasks themselves) */}
+        {!task?.parentId && (
+          <>
+            <Text className={`mb-2 mt-6 text-xs uppercase tracking-wide ${isDark ? 'text-[#A0A0A0]' : 'text-[#6B6B6B]'}`} style={{ fontFamily: 'Inter_600SemiBold' }}>
+              {t('task.subtasks')}
+            </Text>
+            {subtasks.map((sub) => (
+              <Pressable
+                key={sub.id}
+                onPress={() => editingSubtaskId === sub.id ? undefined : handleToggleSubtask(sub.id)}
+                onLongPress={() => handleEditSubtask(sub)}
+                className={`flex-row items-center border-b py-2.5 ${isDark ? 'border-[#3A3A3A]' : 'border-[#E5E7EB]'}`}
+              >
+                <View
+                  className="mr-3 h-5 w-5 items-center justify-center rounded-full border-2"
+                  style={{
+                    borderColor: sub.completed ? colors.bleu.DEFAULT : colors.priority.none,
+                    backgroundColor: sub.completed ? colors.bleu.DEFAULT : 'transparent',
+                  }}
+                >
+                  {sub.completed && <Text className="text-xs text-white" style={{ fontFamily: 'Inter_700Bold' }}>✓</Text>}
+                </View>
+                {editingSubtaskId === sub.id ? (
+                  <TextInput
+                    value={editingTitle}
+                    onChangeText={setEditingTitle}
+                    onSubmitEditing={handleSaveSubtaskEdit}
+                    onBlur={handleSaveSubtaskEdit}
+                    autoFocus
+                    className={`flex-1 text-base ${isDark ? 'text-[#F5F5F5]' : 'text-[#1A1A1A]'}`}
+                    style={{ fontFamily: 'Inter_400Regular' }}
+                  />
+                ) : (
+                  <Text
+                    className={`flex-1 text-base ${sub.completed ? 'line-through ' + (isDark ? 'text-[#A0A0A0]' : 'text-[#9CA3AF]') : isDark ? 'text-[#F5F5F5]' : 'text-[#1A1A1A]'}`}
+                    style={{ fontFamily: 'Inter_400Regular' }}
+                  >
+                    {sub.title}
+                  </Text>
+                )}
+                <Pressable
+                  onPress={() => handleDeleteSubtask(sub.id)}
+                  className="ml-2 p-1.5"
+                  hitSlop={{ top: 8, bottom: 8, left: 8, right: 8 }}
+                >
+                  <X size={16} color={isDark ? '#A0A0A0' : '#9CA3AF'} />
+                </Pressable>
+              </Pressable>
+            ))}
+
+            {/* Add subtask */}
+            <View className="mt-2 flex-row items-center">
+              <Plus size={18} color={colors.bleu.DEFAULT} />
               <TextInput
-                value={editingTitle}
-                onChangeText={setEditingTitle}
-                onSubmitEditing={handleSaveSubtaskEdit}
-                onBlur={handleSaveSubtaskEdit}
-                autoFocus
-                className={`flex-1 text-base ${isDark ? 'text-[#F5F5F5]' : 'text-[#1A1A1A]'}`}
+                value={newSubtask}
+                onChangeText={setNewSubtask}
+                onSubmitEditing={handleAddSubtask}
+                placeholder={t('task.addSubtask')}
+                placeholderTextColor={isDark ? '#A0A0A0' : '#6B6B6B'}
+                className={`ml-2 flex-1 text-base ${isDark ? 'text-[#F5F5F5]' : 'text-[#1A1A1A]'}`}
                 style={{ fontFamily: 'Inter_400Regular' }}
               />
-            ) : (
-              <Text
-                className={`flex-1 text-base ${sub.completed ? 'line-through ' + (isDark ? 'text-[#A0A0A0]' : 'text-[#9CA3AF]') : isDark ? 'text-[#F5F5F5]' : 'text-[#1A1A1A]'}`}
-                style={{ fontFamily: 'Inter_400Regular' }}
-              >
-                {sub.title}
-              </Text>
-            )}
-            <Pressable
-              onPress={() => handleDeleteSubtask(sub.id)}
-              className="ml-2 p-1.5"
-              hitSlop={{ top: 8, bottom: 8, left: 8, right: 8 }}
-            >
-              <X size={16} color={isDark ? '#A0A0A0' : '#9CA3AF'} />
-            </Pressable>
-          </Pressable>
-        ))}
-
-        {/* Add subtask */}
-        <View className="mt-2 flex-row items-center">
-          <Plus size={18} color={colors.bleu.DEFAULT} />
-          <TextInput
-            value={newSubtask}
-            onChangeText={setNewSubtask}
-            onSubmitEditing={handleAddSubtask}
-            placeholder={t('task.addSubtask')}
-            placeholderTextColor={isDark ? '#A0A0A0' : '#6B6B6B'}
-            className={`ml-2 flex-1 text-base ${isDark ? 'text-[#F5F5F5]' : 'text-[#1A1A1A]'}`}
-            style={{ fontFamily: 'Inter_400Regular' }}
-          />
-        </View>
+            </View>
+          </>
+        )}
 
         <View style={{ height: 32 }} />
       </KeyboardAwareScrollView>
diff --git a/web/src/app/api/tasks/route.ts b/web/src/app/api/tasks/route.ts
index aeaf4a2..ad9c9e7 100644
--- a/web/src/app/api/tasks/route.ts
+++ b/web/src/app/api/tasks/route.ts
@@ -25,16 +25,20 @@ export async function POST(request: Request) {
     return NextResponse.json({ error: 'List not found' }, { status: 404 });
   }
 
-  // If parentId, verify parent task belongs to user
+  // If parentId, verify parent task belongs to user and is not itself a subtask
   if (body.data.parentId) {
     const [parent] = await db
-      .select({ id: slTasks.id })
+      .select({ id: slTasks.id, parentId: slTasks.parentId })
       .from(slTasks)
       .where(and(eq(slTasks.id, body.data.parentId), eq(slTasks.userId, auth.userId)));
 
     if (!parent) {
       return NextResponse.json({ error: 'Parent task not found' }, { status: 404 });
     }
+
+    if (parent.parentId) {
+      return NextResponse.json({ error: 'Cannot create sub-subtasks (max 2 levels)' }, { status: 400 });
+    }
   }
 
   const [task] = await db
diff --git a/web/src/components/TaskItem.tsx b/web/src/components/TaskItem.tsx
index 16627e8..1d0d7a8 100644
--- a/web/src/components/TaskItem.tsx
+++ b/web/src/components/TaskItem.tsx
@@ -261,12 +261,14 @@ export function TaskItem({ task, subtasks = [], depth = 0 }: TaskItemProps) {
                   >
                     {t("task.edit")}
                   </button>
-                  <button
-                    onClick={() => setShowSubtaskForm(!showSubtaskForm)}
-                    className="text-xs text-bleu hover:underline"
-                  >
-                    {t("task.addSubtask")}
-                  </button>
+                  {depth < 1 && (
+                    <button
+                      onClick={() => setShowSubtaskForm(!showSubtaskForm)}
+                      className="text-xs text-bleu hover:underline"
+                    >
+                      {t("task.addSubtask")}
+                    </button>
+                  )}
                   <button
                     onClick={deleteTask}
                     className="text-xs text-rouge hover:underline flex items-center gap-1"