diff --git a/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/ReadFromScratchPadTool.java b/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/ReadFromScratchPadTool.java
index 402342ca7c..70ca8a1072 100644
--- a/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/ReadFromScratchPadTool.java
+++ b/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/ReadFromScratchPadTool.java
@@ -100,18 +100,12 @@ public boolean validate(Map<String, String> parameters) {
      */
     @Override
     public <T> void run(Map<String, String> parameters, ActionListener<T> listener) {
-        // Handle both List<String> and String (JSON) formats for existing notes
+
         List<String> notes;
-        Map rawParameters = parameters;
-        Object existingNotes = rawParameters.get(SCRATCHPAD_NOTES_KEY);
-        if (existingNotes instanceof List) {
-            notes = new ArrayList<>((List<String>) existingNotes);
-        } else if (existingNotes instanceof String) {
-            List<String> parsedNotes = StringUtils.parseStringArrayToList((String) existingNotes);
-            notes = parsedNotes != null ? new ArrayList<>(parsedNotes) : new ArrayList<>();
-        } else {
-            notes = new ArrayList<>();
-        }
+        String existingNotes = parameters.getOrDefault(SCRATCHPAD_NOTES_KEY, "[]");
+
+        List<String> parsedNotes = StringUtils.parseStringArrayToList(existingNotes);
+        notes = parsedNotes != null ? new ArrayList<>(parsedNotes) : new ArrayList<>();
 
         String persistentNotes = parameters.getOrDefault(PERSISTENT_NOTES_KEY, "");
 
@@ -119,7 +113,7 @@ public <T> void run(Map<String, String> parameters, ActionListener<T> listener)
             notes.add(persistentNotes);
         }
 
-        rawParameters.put(SCRATCHPAD_NOTES_KEY, notes);
+        parameters.put(SCRATCHPAD_NOTES_KEY, StringUtils.toJson(notes));
 
         if (notes.isEmpty()) {
             listener.onResponse((T) "Scratchpad is empty.");
diff --git a/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/WriteToScratchPadTool.java b/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/WriteToScratchPadTool.java
index 82d3e2148b..ba15fbb8b3 100644
--- a/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/WriteToScratchPadTool.java
+++ b/ml-algorithms/src/main/java/org/opensearch/ml/engine/tools/WriteToScratchPadTool.java
@@ -111,21 +111,15 @@ public <T> void run(Map<String, String> parameters, ActionListener<T> listener)
             return;
         }
 
-        // Handle both List<String> and String (JSON) formats for existing notes
         List<String> notes;
-        Map rawParameters = parameters;
-        Object existingNotes = rawParameters.get(SCRATCHPAD_NOTES_KEY);
-        if (existingNotes instanceof List) {
-            notes = new ArrayList<>((List<String>) existingNotes);
-        } else if (existingNotes instanceof String) {
-            List<String> parsedNotes = StringUtils.parseStringArrayToList((String) existingNotes);
-            notes = parsedNotes != null ? new ArrayList<>(parsedNotes) : new ArrayList<>();
-        } else {
-            notes = new ArrayList<>();
-        }
+        ;
+        String existingNotes = parameters.getOrDefault(SCRATCHPAD_NOTES_KEY, "[]");
+
+        List<String> parsedNotes = StringUtils.parseStringArrayToList(existingNotes);
+        notes = parsedNotes != null ? new ArrayList<>(parsedNotes) : new ArrayList<>();
 
         notes.add(currentNote);
-        rawParameters.put(SCRATCHPAD_NOTES_KEY, notes);
+        parameters.put(SCRATCHPAD_NOTES_KEY, StringUtils.toJson(notes));
 
         if (returnHistory) {
             String fullNotesFormatted = "- " + String.join("\n- ", notes);
diff --git a/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/ReadFromScratchPadToolTests.java b/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/ReadFromScratchPadToolTests.java
index 6324e38830..b94960e107 100644
--- a/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/ReadFromScratchPadToolTests.java
+++ b/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/ReadFromScratchPadToolTests.java
@@ -10,8 +10,6 @@
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.verify;
 
-import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -83,89 +81,89 @@ public void testValidate() {
 
     @Test
     public void testRun_NoNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        tool.run((Map) parameters, listener);
+        Map<String, String> parameters = new HashMap<>();
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Scratchpad is empty.", captor.getValue());
-        assertEquals(new ArrayList<>(), parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_WithScratchpadNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>(Arrays.asList("existing note")));
-        tool.run((Map) parameters, listener);
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Notes from scratchpad:\n- existing note", captor.getValue());
-        assertEquals(Arrays.asList("existing note"), parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"existing note\"]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_WithPersistentNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>()); // Initialize with empty list
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[]");
         parameters.put(ReadFromScratchPadTool.PERSISTENT_NOTES_KEY, "persistent note");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Notes from scratchpad:\n- persistent note", captor.getValue());
-        assertEquals(Arrays.asList("persistent note"), parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"persistent note\"]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_WithBothNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>(Arrays.asList("existing note")));
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
         parameters.put(ReadFromScratchPadTool.PERSISTENT_NOTES_KEY, "persistent note");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Notes from scratchpad:\n- existing note\n- persistent note", captor.getValue());
-        assertEquals(Arrays.asList("existing note", "persistent note"), parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"existing note\",\"persistent note\"]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_WithDuplicatePersistentNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>(Arrays.asList("existing note", "persistent note")));
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\",\"persistent note\"]");
         parameters.put(ReadFromScratchPadTool.PERSISTENT_NOTES_KEY, "persistent note");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Notes from scratchpad:\n- existing note\n- persistent note", captor.getValue());
-        assertEquals(Arrays.asList("existing note", "persistent note"), parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"existing note\",\"persistent note\"]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_WithNonListScratchpadNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "not a list");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Scratchpad is empty.", captor.getValue());
-        assertEquals(new ArrayList<>(), parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_WithJsonStringNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"json note\"]");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Notes from scratchpad:\n- json note", captor.getValue());
-        assertEquals(Arrays.asList("json note"), parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"json note\"]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_WithEmptyPersistentNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>(Arrays.asList("existing note")));
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
         parameters.put(ReadFromScratchPadTool.PERSISTENT_NOTES_KEY, "");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Notes from scratchpad:\n- existing note", captor.getValue());
@@ -173,15 +171,52 @@ public void testRun_WithEmptyPersistentNotes() {
 
     @Test
     public void testRun_WithNullPersistentNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>(Arrays.asList("existing note")));
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
         parameters.put(ReadFromScratchPadTool.PERSISTENT_NOTES_KEY, null);
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Notes from scratchpad:\n- existing note", captor.getValue());
     }
 
+    @Test
+    public void testRun_StringConversion_EmptyArray() {
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[]");
+        tool.run(parameters, listener);
+
+        ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
+        verify(listener).onResponse(captor.capture());
+        assertEquals("Scratchpad is empty.", captor.getValue());
+        assertEquals("[]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+    }
+
+    @Test
+    public void testRun_StringConversion_WithJsonArray() {
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"note1\",\"note2\"]");
+        tool.run(parameters, listener);
+
+        ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
+        verify(listener).onResponse(captor.capture());
+        assertEquals("Notes from scratchpad:\n- note1\n- note2", captor.getValue());
+        assertEquals("[\"note1\",\"note2\"]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+    }
+
+    @Test
+    public void testRun_StringConversion_AddPersistentNote() {
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing\"]");
+        parameters.put(ReadFromScratchPadTool.PERSISTENT_NOTES_KEY, "new note");
+        tool.run(parameters, listener);
+
+        ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
+        verify(listener).onResponse(captor.capture());
+        assertEquals("Notes from scratchpad:\n- existing\n- new note", captor.getValue());
+        assertEquals("[\"existing\",\"new note\"]", parameters.get(ReadFromScratchPadTool.SCRATCHPAD_NOTES_KEY));
+    }
+
     @Test
     public void testFactory() {
         ReadFromScratchPadTool.Factory factory = ReadFromScratchPadTool.Factory.getInstance();
diff --git a/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/WriteToScratchPadToolTests.java b/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/WriteToScratchPadToolTests.java
index 5ac432e265..35419d1872 100644
--- a/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/WriteToScratchPadToolTests.java
+++ b/ml-algorithms/src/test/java/org/opensearch/ml/engine/tools/WriteToScratchPadToolTests.java
@@ -11,8 +11,6 @@
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.verify;
 
-import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -90,33 +88,33 @@ public void testValidate() {
 
     @Test
     public void testRun_Success_NoExistingNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
 
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Wrote to scratchpad: new note", captor.getValue());
-        assertEquals(Arrays.asList("new note"), parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_Success_WithExistingNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
-        parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>(Arrays.asList("existing note")));
-        tool.run((Map) parameters, listener);
+        parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
+        tool.run(parameters, listener);
 
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Wrote to scratchpad: new note", captor.getValue());
-        assertEquals(Arrays.asList("existing note", "new note"), parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"existing note\",\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_Failure_NoNotes() {
-        Map<String, Object> parameters = new HashMap<>();
-        tool.run((Map) parameters, listener);
+        Map<String, String> parameters = new HashMap<>();
+        tool.run(parameters, listener);
 
         ArgumentCaptor<Exception> captor = ArgumentCaptor.forClass(Exception.class);
         verify(listener).onFailure(captor.capture());
@@ -126,9 +124,9 @@ public void testRun_Failure_NoNotes() {
 
     @Test
     public void testRun_Failure_EmptyNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
 
         ArgumentCaptor<Exception> captor = ArgumentCaptor.forClass(Exception.class);
         verify(listener).onFailure(captor.capture());
@@ -138,69 +136,109 @@ public void testRun_Failure_EmptyNotes() {
 
     @Test
     public void testRun_Success_ReturnHistory_WithExistingNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
-        parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, new ArrayList<>(Arrays.asList("existing note")));
+        parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
         parameters.put(WriteToScratchPadTool.RETURN_HISTORY_KEY, "true");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
 
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Scratchpad updated. Full content:\n- existing note\n- new note", captor.getValue());
-        assertEquals(Arrays.asList("existing note", "new note"), parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"existing note\",\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_Success_ReturnHistory_NoExistingNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
         parameters.put(WriteToScratchPadTool.RETURN_HISTORY_KEY, "true");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
 
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Scratchpad updated. Full content:\n- new note", captor.getValue());
-        assertEquals(Arrays.asList("new note"), parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_Success_NonListScratchpadNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
         parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, "not a list");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
 
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Wrote to scratchpad: new note", captor.getValue());
-        assertEquals(Arrays.asList("new note"), parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_Success_WithJsonStringNotes() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
         parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
 
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Wrote to scratchpad: new note", captor.getValue());
-        assertEquals(Arrays.asList("existing note", "new note"), parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+        assertEquals("[\"existing note\",\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
     }
 
     @Test
     public void testRun_Success_ReturnHistory_False() {
-        Map<String, Object> parameters = new HashMap<>();
+        Map<String, String> parameters = new HashMap<>();
         parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
         parameters.put(WriteToScratchPadTool.RETURN_HISTORY_KEY, "false");
-        tool.run((Map) parameters, listener);
+        tool.run(parameters, listener);
 
         ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
         verify(listener).onResponse(captor.capture());
         assertEquals("Wrote to scratchpad: new note", captor.getValue());
     }
 
+    @Test
+    public void testRun_StringConversion_EmptyArray() {
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(WriteToScratchPadTool.NOTES_KEY, "test note");
+        parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, "[]");
+        tool.run(parameters, listener);
+
+        ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
+        verify(listener).onResponse(captor.capture());
+        assertEquals("Wrote to scratchpad: test note", captor.getValue());
+        assertEquals("[\"test note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+    }
+
+    @Test
+    public void testRun_StringConversion_WithJsonArray() {
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
+        parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing note\"]");
+        tool.run(parameters, listener);
+
+        ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
+        verify(listener).onResponse(captor.capture());
+        assertEquals("Wrote to scratchpad: new note", captor.getValue());
+        assertEquals("[\"existing note\",\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+    }
+
+    @Test
+    public void testRun_StringConversion_ReturnHistory() {
+        Map<String, String> parameters = new HashMap<>();
+        parameters.put(WriteToScratchPadTool.NOTES_KEY, "new note");
+        parameters.put(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY, "[\"existing\"]");
+        parameters.put(WriteToScratchPadTool.RETURN_HISTORY_KEY, "true");
+        tool.run(parameters, listener);
+
+        ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
+        verify(listener).onResponse(captor.capture());
+        assertEquals("Scratchpad updated. Full content:\n- existing\n- new note", captor.getValue());
+        assertEquals("[\"existing\",\"new note\"]", parameters.get(WriteToScratchPadTool.SCRATCHPAD_NOTES_KEY));
+    }
+
     @Test
     public void testFactory() {
         WriteToScratchPadTool.Factory factory = WriteToScratchPadTool.Factory.getInstance();