diff --git a/libs/sutsim/c/sutsim.c b/libs/sutsim/c/sutsim.c
index b9e8020..b0f7037 100644
--- a/libs/sutsim/c/sutsim.c
+++ b/libs/sutsim/c/sutsim.c
@@ -3,13 +3,20 @@
 #include <stdlib.h>
 #include <stdio.h>
 
+/* Forward declarations */
 extern void sut_init_hook(void);
 extern void sut_tick_hook(void);
 
+/* PRIVATE DATA */
 static sutsim_tagList_S tag_list = {0};
 
+/* PRIVATE FUNCTION DECLARATIONS */
+static sutsim_tagEntry_S* sutsim_find_tag(const char* tag);
+
+/* PUBLIC FUNCTIONS */
 void sutsim_init(void) {
     tag_list.head = NULL;
+    tag_list.tail = NULL;
     tag_list.count = 0;
     tag_list.initialized = true;
 
@@ -21,85 +28,80 @@ void sutsim_tick(void) {
     sut_tick_hook();
 }
 
-int sutsim_add_tag(const char* tag, void* data, uint32_t size, sutsim_dataType_E type) {
+bool sutsim_add_tag(const char* tag, void* data, uint32_t size, sutsim_dataType_E type) {
+    if (sutsim_find_tag(tag)) {
+        return false;  // Tag already exists
+    }
+
     sutsim_tagEntry_S* new_entry = (sutsim_tagEntry_S*)malloc(sizeof(sutsim_tagEntry_S));
     if (!new_entry) {
-        return -1;  // Memory allocation failure
+        return false;  // Memory allocation failure
     }
 
-    new_entry->id = tag_list.count;
-    new_entry->tag = tag;
-    new_entry->data = data;  // Directly use the user-provided buffer
-    new_entry->size = size;
-    new_entry->type = type;
+    new_entry->id            = tag_list.count;
+    new_entry->tag           = tag;
+    new_entry->data          = data;  // Directly use the user-provided buffer
+    new_entry->size          = size;
+    new_entry->type          = type;
     new_entry->subscriber_cb = NULL;
-    new_entry->next = NULL;
+    new_entry->next          = NULL;
 
     if (tag_list.head == NULL) {
         tag_list.head = new_entry;
+        tag_list.tail = new_entry;
     } else {
-        sutsim_tagEntry_S* current = tag_list.head;
-        while (current->next != NULL) {
-            current = current->next;
-        }
-        current->next = new_entry;
+        tag_list.tail->next = new_entry;
+        tag_list.tail = new_entry;
     }
 
     tag_list.count++;
-    return new_entry->id;
+
+    return true;
 }
 
-void sutsim_subscribe_to_tag(const char* tag, sutsim_TagCallback subscriber_cb) {
-    sutsim_tagEntry_S* current = tag_list.head;
-    while (current != NULL) {
-        if (strcmp(tag, current->tag) == 0) {
-            current->subscriber_cb = subscriber_cb;
-            return;
-        }
-        current = current->next;
+bool sutsim_subscribe_to_tag(const char* tag, sutsim_TagCallback subscriber_cb) {
+    sutsim_tagEntry_S* tagEntry = sutsim_find_tag(tag);
+
+    if (tagEntry) {
+        tagEntry->subscriber_cb = subscriber_cb;
+        return true;
     }
+
+    return false;  // Tag not found
 }
 
 bool sutsim_write(const char* tag, const void* data, uint32_t size) {
-    sutsim_tagEntry_S* current = tag_list.head;
-    while (current != NULL) {
-        if (strcmp(tag, current->tag) == 0) {
-            if (size != current->size) {
-                return false;  // Size mismatch
-            }
+    sutsim_tagEntry_S* tagEntry = sutsim_find_tag(tag);
 
-            // Update the user-provided tag data buffer
-            if (current->data) {
-                memcpy(current->data, data, size);
-            }
+    if (tagEntry) {
+        if (size != tagEntry->size) {
+            return false;  // Size mismatch
+        }
 
-            if (current->subscriber_cb) {
-                current->subscriber_cb(tag, data, size);
-            }
+        memcpy(tagEntry->data, data, size);
 
-            return true;
+        if (tagEntry->subscriber_cb) {
+            tagEntry->subscriber_cb(tag, data, size);
         }
 
-        current = current->next;
+        return true;
     }
 
     return false;  // Tag not found
 }
 
 bool sutsim_read(const char* tag, void* buffer, uint32_t size) {
-    sutsim_tagEntry_S* current = tag_list.head;
-    while (current != NULL) {
-        if (strcmp(tag, current->tag) == 0) {
-            if (size != current->size) {
-                return false;  // Size mismatch
-            }
+    sutsim_tagEntry_S* tagEntry = sutsim_find_tag(tag);
 
-            // Copy the data from the tag's buffer (user-provided)
-            memcpy(buffer, current->data, size);
-            return true;
+    if (tagEntry) {
+        if (size != tagEntry->size) {
+            return false;  // Size mismatch
         }
-        current = current->next;
+
+        memcpy(buffer, tagEntry->data, size);
+        return true;
     }
+
     return false;  // Tag not found
 }
 
@@ -112,5 +114,18 @@ void sutsim_cleanup(void) {
         current = next;
     }
     tag_list.head = NULL;
+    tag_list.tail = NULL;
     tag_list.count = 0;
 }
+
+static sutsim_tagEntry_S* sutsim_find_tag(const char* tag) {
+    sutsim_tagEntry_S* current = tag_list.head;
+    while (current != NULL) {
+        if (strcmp(tag, current->tag) == 0) {
+            return current;
+        }
+        current = current->next;
+    }
+
+    return NULL;
+}
diff --git a/libs/sutsim/c/sutsim.h b/libs/sutsim/c/sutsim.h
index 483b3b9..3f9ad9c 100644
--- a/libs/sutsim/c/sutsim.h
+++ b/libs/sutsim/c/sutsim.h
@@ -31,6 +31,7 @@ typedef struct sutsim_tagEntry {
 typedef struct {
     bool initialized;
     sutsim_tagEntry_S* head;
+    sutsim_tagEntry_S* tail;
     uint32_t count;
 } sutsim_tagList_S;
 
@@ -40,10 +41,10 @@ void sutsim_init(void);
 void sutsim_tick(void);
 
 // Add a tag entry (user provides a pointer to the data buffer)
-int sutsim_add_tag(const char* tag, void* data, uint32_t size, sutsim_dataType_E type);
+bool sutsim_add_tag(const char* tag, void* data, uint32_t size, sutsim_dataType_E type);
 
 // Subscribe to a tag (register a callback for tag updates)
-void sutsim_subscribe_to_tag(const char* tag, sutsim_TagCallback subscriber_cb);
+bool sutsim_subscribe_to_tag(const char* tag, sutsim_TagCallback subscriber_cb);
 
 // Write data to a tag
 bool sutsim_write(const char* tag, const void* data, uint32_t size);
diff --git a/sim/core/Simulator.cpp b/sim/core/Simulator.cpp
index 24fa773..5aed0e4 100644
--- a/sim/core/Simulator.cpp
+++ b/sim/core/Simulator.cpp
@@ -32,7 +32,7 @@ void Simulator::init_sut(const std::string& sut_name, const std::string& lib_pat
     context.sutsim_tick = reinterpret_cast<void (*)()>(dlsym(context.lib_handle, "sutsim_tick"));
     context.sutsim_read = reinterpret_cast<bool (*)(const char*, void*, uint32_t)>(dlsym(context.lib_handle, "sutsim_read"));
     context.sutsim_write = reinterpret_cast<bool (*)(const char*, const void*, uint32_t)>(dlsym(context.lib_handle, "sutsim_write"));
-    context.sutsim_subscribe_to_tag = reinterpret_cast<void (*)(const char*, void*)>(dlsym(context.lib_handle, "sutsim_subscribe_to_tag"));
+    context.sutsim_subscribe_to_tag = reinterpret_cast<bool (*)(const char*, void*)>(dlsym(context.lib_handle, "sutsim_subscribe_to_tag"));
 
     if (!context.sutsim_init || !context.sutsim_tick || !context.sutsim_read || !context.sutsim_write || !context.sutsim_subscribe_to_tag) {
         throw std::runtime_error("Failed to load required symbols from SUT library.");
diff --git a/sim/core/SutContext.hpp b/sim/core/SutContext.hpp
index 6d7fb3d..46bf49f 100644
--- a/sim/core/SutContext.hpp
+++ b/sim/core/SutContext.hpp
@@ -14,7 +14,7 @@ class SutContext {
     void* lib_handle;
     void (*sutsim_init)(void);
     void (*sutsim_tick)(void);
-    void (*sutsim_subscribe_to_tag)(const char*, void*);
+    bool (*sutsim_subscribe_to_tag)(const char*, void*);
     bool (*sutsim_write)(const char*, const void*, uint32_t);
     bool (*sutsim_read)(const char*, void*, uint32_t);