diff --git a/Assets/DiscoverOverlayController.cs b/Assets/DiscoverOverlayController.cs
index 456d74a..2c49c87 100644
--- a/Assets/DiscoverOverlayController.cs
+++ b/Assets/DiscoverOverlayController.cs
@@ -5,14 +5,43 @@ public class DiscoverOverlayController : MonoBehaviour
 {
     public GameObject overlayPanel;
     public RectTransform overlayContent;
+    public TopologyBuilder topologyBuilder;
 
     public void ShowOverlay()
     {
-        if (overlayPanel != null)
+        if (overlayPanel == null) return;
+
+        EnsureScrollRect();
+        ClearContent();
+
+        if (topologyBuilder == null)
+            topologyBuilder = FindObjectOfType<TopologyBuilder>();
+
+        bool useMock = topologyBuilder != null && topologyBuilder.mockControlLibrary;
+
+        if (useMock)
         {
-            EnsureScrollRect();
-            overlayPanel.SetActive(true);
+            PopulateMockLeaders();
         }
+        else
+        {
+            int[] leaders = null;
+            try
+            {
+                leaders = ControlLibrary.getRobotLeaders();
+            }
+            catch (System.Exception ex)
+            {
+                Debug.LogError($"[Discover] getRobotLeaders failed: {ex.Message}");
+            }
+
+            if (leaders != null && leaders.Length > 0)
+                PopulateLeaders(leaders);
+            else
+                CreateLabel("No leaders found. Is the hardware connected?");
+        }
+
+        overlayPanel.SetActive(true);
     }
 
     public void HideOverlay()
@@ -22,6 +51,195 @@ public class DiscoverOverlayController : MonoBehaviour
             overlayPanel.SetActive(false);
     }
 
+    void PopulateLeaders(int[] leaderIds)
+    {
+        float buttonHeight = 60f;
+        float spacing = 10f;
+        Font font = Resources.GetBuiltinResource<Font>("LegacyRuntime.ttf");
+
+        for (int i = 0; i < leaderIds.Length; i++)
+        {
+            int leaderId = leaderIds[i];
+
+            GameObject btnGo = new GameObject($"LeaderBtn_{leaderId}", typeof(RectTransform));
+            btnGo.transform.SetParent(overlayContent, false);
+
+            RectTransform rt = btnGo.GetComponent<RectTransform>();
+            rt.anchorMin = new Vector2(0.05f, 1f);
+            rt.anchorMax = new Vector2(0.95f, 1f);
+            rt.pivot = new Vector2(0.5f, 1f);
+            rt.anchoredPosition = new Vector2(0f, -(spacing + i * (buttonHeight + spacing)));
+            rt.sizeDelta = new Vector2(0f, buttonHeight);
+
+            Image bg = btnGo.AddComponent<Image>();
+            bg.color = new Color(0.2f, 0.2f, 0.2f, 1f);
+
+            Button btn = btnGo.AddComponent<Button>();
+            var colors = btn.colors;
+            colors.highlightedColor = new Color(0.35f, 0.35f, 0.35f, 1f);
+            colors.pressedColor = new Color(0.5f, 0.5f, 0.5f, 1f);
+            btn.colors = colors;
+
+            GameObject txtGo = new GameObject("Text", typeof(RectTransform));
+            txtGo.transform.SetParent(btnGo.transform, false);
+            RectTransform txtRt = txtGo.GetComponent<RectTransform>();
+            txtRt.anchorMin = Vector2.zero;
+            txtRt.anchorMax = Vector2.one;
+            txtRt.offsetMin = Vector2.zero;
+            txtRt.offsetMax = Vector2.zero;
+
+            Text txt = txtGo.AddComponent<Text>();
+            txt.text = $"Leader {leaderId}";
+            txt.font = font;
+            txt.fontSize = 22;
+            txt.alignment = TextAnchor.MiddleCenter;
+            txt.color = Color.white;
+
+            btn.onClick.AddListener(() => OnLeaderSelected(leaderId));
+        }
+
+        float totalHeight = leaderIds.Length * (buttonHeight + spacing) + spacing;
+        overlayContent.sizeDelta = new Vector2(overlayContent.sizeDelta.x, totalHeight);
+    }
+
+    void PopulateMockLeaders()
+    {
+        float buttonHeight = 60f;
+        float spacing = 10f;
+        Font font = Resources.GetBuiltinResource<Font>("LegacyRuntime.ttf");
+
+        int i = 0;
+        foreach (var kvp in TopologyBuilder.MockLeaders)
+        {
+            int id = kvp.Key;
+            string jsonName = kvp.Value;
+            int idx = i;
+
+            GameObject btnGo = new GameObject($"MockLeaderBtn_{id}", typeof(RectTransform));
+            btnGo.transform.SetParent(overlayContent, false);
+
+            RectTransform rt = btnGo.GetComponent<RectTransform>();
+            rt.anchorMin = new Vector2(0.05f, 1f);
+            rt.anchorMax = new Vector2(0.95f, 1f);
+            rt.pivot = new Vector2(0.5f, 1f);
+            rt.anchoredPosition = new Vector2(0f, -(spacing + idx * (buttonHeight + spacing)));
+            rt.sizeDelta = new Vector2(0f, buttonHeight);
+
+            Image bg = btnGo.AddComponent<Image>();
+            bg.color = new Color(0.2f, 0.2f, 0.2f, 1f);
+
+            Button btn = btnGo.AddComponent<Button>();
+            var colors = btn.colors;
+            colors.highlightedColor = new Color(0.35f, 0.35f, 0.35f, 1f);
+            colors.pressedColor = new Color(0.5f, 0.5f, 0.5f, 1f);
+            btn.colors = colors;
+
+            GameObject txtGo = new GameObject("Text", typeof(RectTransform));
+            txtGo.transform.SetParent(btnGo.transform, false);
+            RectTransform txtRt = txtGo.GetComponent<RectTransform>();
+            txtRt.anchorMin = Vector2.zero;
+            txtRt.anchorMax = Vector2.one;
+            txtRt.offsetMin = Vector2.zero;
+            txtRt.offsetMax = Vector2.zero;
+
+            Text txt = txtGo.AddComponent<Text>();
+            txt.text = $"Mock Leader {id}  ({jsonName})";
+            txt.font = font;
+            txt.fontSize = 22;
+            txt.alignment = TextAnchor.MiddleCenter;
+            txt.color = Color.white;
+
+            string capturedJsonName = jsonName;
+            btn.onClick.AddListener(() => OnMockLeaderSelected(capturedJsonName));
+            i++;
+        }
+
+        float totalHeight = TopologyBuilder.MockLeaders.Count * (buttonHeight + spacing) + spacing;
+        overlayContent.sizeDelta = new Vector2(overlayContent.sizeDelta.x, totalHeight);
+    }
+
+    void OnMockLeaderSelected(string jsonFileName)
+    {
+        Debug.Log($"[Discover] Mock leader selected, loading {jsonFileName}...");
+
+        if (topologyBuilder == null)
+            topologyBuilder = FindObjectOfType<TopologyBuilder>();
+
+        if (topologyBuilder == null)
+        {
+            Debug.LogError("[Discover] No TopologyBuilder found in scene!");
+            HideOverlay();
+            return;
+        }
+
+        try
+        {
+            topologyBuilder.BuildTopologyFromJsonFile(jsonFileName);
+            Debug.Log($"[Discover] Mock topology built from {jsonFileName}");
+
+            var cam = FindObjectOfType<UserCameraControl>();
+            if (cam != null) cam.FindModuleStructure();
+        }
+        catch (System.Exception ex)
+        {
+            Debug.LogError($"[Discover] Failed to build mock topology: {ex.Message}");
+        }
+
+        HideOverlay();
+    }
+
+    void OnLeaderSelected(int leaderId)
+    {
+        Debug.Log($"[Discover] Selected leader {leaderId}, building topology...");
+
+        if (topologyBuilder == null)
+        {
+            topologyBuilder = FindObjectOfType<TopologyBuilder>();
+        }
+
+        if (topologyBuilder == null)
+        {
+            Debug.LogError("[Discover] No TopologyBuilder found in scene!");
+            HideOverlay();
+            return;
+        }
+
+        try
+        {
+            topologyBuilder.BuildTopologyFromLeader(leaderId);
+            Debug.Log($"[Discover] Topology built successfully for leader {leaderId}");
+
+            var cam = FindObjectOfType<UserCameraControl>();
+            if (cam != null) cam.FindModuleStructure();
+        }
+        catch (System.Exception ex)
+        {
+            Debug.LogError($"[Discover] Failed to build topology for leader {leaderId}: {ex.Message}");
+        }
+
+        HideOverlay();
+    }
+
+    void CreateLabel(string message)
+    {
+        Font font = Resources.GetBuiltinResource<Font>("LegacyRuntime.ttf");
+        GameObject go = new GameObject("InfoLabel", typeof(RectTransform));
+        go.transform.SetParent(overlayContent, false);
+        RectTransform rt = go.GetComponent<RectTransform>();
+        rt.anchorMin = new Vector2(0.05f, 1f);
+        rt.anchorMax = new Vector2(0.95f, 1f);
+        rt.pivot = new Vector2(0.5f, 1f);
+        rt.anchoredPosition = new Vector2(0f, -20f);
+        rt.sizeDelta = new Vector2(0f, 50f);
+
+        Text txt = go.AddComponent<Text>();
+        txt.text = message;
+        txt.font = font;
+        txt.fontSize = 20;
+        txt.alignment = TextAnchor.MiddleCenter;
+        txt.color = new Color(1f, 0.6f, 0.6f, 1f);
+    }
+
     void EnsureScrollRect()
     {
         if (overlayContent == null) return;
diff --git a/Assets/Module/DiscoveryButton.cs b/Assets/Module/DiscoveryButton.cs
index e9698fe..b6c69e0 100644
--- a/Assets/Module/DiscoveryButton.cs
+++ b/Assets/Module/DiscoveryButton.cs
@@ -19,16 +19,7 @@ public class DiscoveryButton : MonoBehaviour
 
     public void OnDiscoveryPressed()
     {
-        if (topologyBuilder != null)
-        {
-            Debug.Log("Discovery button pressed.");
-            topologyBuilder.BuildTopologyFromJson();
-            FocusCameraOnTopology();
-        }
-        else
-        {
-            Debug.LogError("TopologyBuilder is not assigned!");
-        }
+        Debug.Log("Discovery button pressed – topology building deferred to overlay selection.");
     }
 
     void FocusCameraOnTopology()
diff --git a/Assets/Module/TopologyBuilder.cs b/Assets/Module/TopologyBuilder.cs
index b9ddf39..5d44cd1 100644
--- a/Assets/Module/TopologyBuilder.cs
+++ b/Assets/Module/TopologyBuilder.cs
@@ -23,6 +23,10 @@ public class TopologyBuilder : MonoBehaviour
     [Tooltip("JSON file name (without .json) in Resources folder. e.g. 'mockData' or 'mockDataSimple'")]
     public string jsonFileName = "mockDataNewConfig";
 
+    [Header("Mock Control Library")]
+    [Tooltip("When true, Discover overlay shows mock leaders backed by JSON files instead of calling the real native library.")]
+    public bool mockControlLibrary = false;
+
     public static Dictionary<string, GameObject> idToInstance = new();
     public static bool _skipControlLibraryCalls = true;
 
@@ -126,6 +130,96 @@ public class TopologyBuilder : MonoBehaviour
         BuildTopologyFromGraph(graph);
     }
 
+    public static readonly Dictionary<int, string> MockLeaders = new()
+    {
+        { 1, "mockData" },
+        { 2, "mockDataWithDC" }
+    };
+
+    public void BuildTopologyFromJsonFile(string fileName)
+    {
+        TopologyGraph graph = new TopologyGraph();
+        Dictionary<int, ModuleType> idToType = new();
+
+        TextAsset jsonAsset = Resources.Load<TextAsset>(fileName);
+        if (jsonAsset == null) { Debug.LogError($"JSON not found: Resources/{fileName}.json"); return; }
+        JsonTopologyGraph jsonGraph = JsonUtility.FromJson<JsonTopologyGraph>(jsonAsset.text);
+        if (jsonGraph?.Modules == null || jsonGraph.Modules.Count == 0) { Debug.LogError("JSON has no modules"); return; }
+
+        Dictionary<string, int> stringToIntId = new();
+        int nextIntId = 1;
+        foreach (var m in jsonGraph.Modules)
+        {
+            if (!stringToIntId.ContainsKey(m.Id)) stringToIntId[m.Id] = nextIntId++;
+            int intId = stringToIntId[m.Id];
+            ModuleType mt = ParseModuleType(m.Type);
+            idToType[intId] = mt;
+            graph.Modules.Add(new ModuleData { Id = intId, Type = mt.ToString(), Degree = m.Degree });
+        }
+        if (jsonGraph.Connections != null)
+            foreach (var c in jsonGraph.Connections)
+            {
+                if (!stringToIntId.TryGetValue(c.FromModuleId, out int fromId) || !stringToIntId.TryGetValue(c.ToModuleId, out int toId)) continue;
+                Orientation o = c.Orientation == 90 ? Orientation.Deg90 : c.Orientation == 180 ? Orientation.Deg180 : c.Orientation == 270 ? Orientation.Deg270 : Orientation.Deg0;
+                graph.Connections.Add(new Connection { FromModuleId = fromId, ToModuleId = toId, FromSocket = c.FromSocket ?? "MaleSocket", ToSocket = c.ToSocket ?? "FemaleSocket", Orientation = o });
+            }
+
+        Debug.Log($"[TopologyBuilder] Built from JSON file: {fileName}");
+        _skipControlLibraryCalls = true;
+        BuildTopologyFromGraph(graph);
+    }
+
+    public void BuildTopologyFromLeader(int leaderId)
+    {
+        TopologyGraph graph = new TopologyGraph();
+        Dictionary<int, ModuleType> idToType = new();
+
+        RobotConfiguration config = ControlLibrary.getRobotConfiguration(leaderId);
+        int moduleCount = config.ModulesLength;
+        for (int i = 0; i < moduleCount; i++)
+        {
+            var n_module = config.Modules(i);
+            if (n_module != null)
+            {
+                var module = n_module.Value;
+                ModuleType moduleType = Enum.Parse<ModuleType>(module.ModuleType.ToString());
+                float degree = module.ConfigurationAsMotorState().Angle;
+                if (moduleType == ModuleType.SERVO_1 || moduleType == ModuleType.SERVO_2)
+                    degree = 90;
+                graph.Modules.Add(new ModuleData { Id = module.Id, Type = module.ModuleType.ToString(), Degree = degree });
+                idToType.Add(module.Id, module.ModuleType);
+            }
+        }
+        int connectionCount = config.ConnectionsLength;
+        for (int i = 0; i < connectionCount; i++)
+        {
+            var n_connection = config.Connections(i);
+            if (n_connection != null)
+            {
+                var connection = n_connection.Value;
+                if (connection.FromSocket == 0) continue;
+                graph.Connections.Add(new Connection
+                {
+                    FromModuleId = connection.FromModuleId,
+                    FromSocket =
+                        idToType[connection.FromModuleId] == ModuleType.SPLITTER ||
+                        idToType[connection.FromModuleId] == ModuleType.SPLITTER_2 ||
+                        idToType[connection.FromModuleId] == ModuleType.SPLITTER_3 ||
+                        idToType[connection.FromModuleId] == ModuleType.SPLITTER_4
+                            ? "MaleSocket" + (connection.FromSocket == 0 ? "" : connection.FromSocket)
+                            : "MaleSocket",
+                    ToModuleId = connection.ToModuleId,
+                    ToSocket = "FemaleSocket",
+                    Orientation = connection.Orientation
+                });
+            }
+        }
+        _skipControlLibraryCalls = false;
+
+        Debug.Log($"[TopologyBuilder] Building from leader {leaderId}: {graph.Modules.Count} modules, {graph.Connections.Count} connections");
+        BuildTopologyFromGraph(graph);
+    }
+
     private static ModuleType ParseModuleType(string typeString)
     {
         if (string.IsNullOrEmpty(typeString)) return ModuleType.SPLITTER;
diff --git a/Assets/Scenes/SampleScene.unity b/Assets/Scenes/SampleScene.unity
index cd11959..3679571 100644
--- a/Assets/Scenes/SampleScene.unity
+++ b/Assets/Scenes/SampleScene.unity
@@ -2667,6 +2667,7 @@ MonoBehaviour:
   useJsonFile: 0
   skipControlLibraryCalls: 0
   jsonFileName: mockData
+  mockControlLibrary: 0
 --- !u!4 &387671720
 Transform:
   m_ObjectHideFlags: 0
@@ -21345,6 +21346,7 @@ MonoBehaviour:
   m_EditorClassIdentifier: 
   overlayPanel: {fileID: 8840000001}
   overlayContent: {fileID: 8840000042}
+  topologyBuilder: {fileID: 387671719}
 --- !u!1 &168756400964845240
 GameObject:
   m_ObjectHideFlags: 0