diff --git a/.DS_Store b/.DS_Store
index 25bf41a..cf2e7f8 100644
Binary files a/.DS_Store and b/.DS_Store differ
diff --git a/DYNAMIC_SHEET_FIX.md b/DYNAMIC_SHEET_FIX.md
new file mode 100644
index 0000000..7a18ccf
--- /dev/null
+++ b/DYNAMIC_SHEET_FIX.md
@@ -0,0 +1,118 @@
+# Dynamic Sheet Handling Fix
+
+## Problem
+The application was failing with "Sheet 'US URGENT' not found in data" error when working with Excel files that don't contain a sheet named 'US URGENT'. The code needed to be made dynamic to work with any sheet names.
+
+## Root Cause
+The issue was in the web interface JavaScript where:
+1. On page load, `analyzeData()` was called immediately
+2. The sheet filter dropdown was empty at that time
+3. An empty string was being sent as `sheet_filter` to the backend
+4. The backend wasn't properly handling empty strings
+
+## Fixes Applied
+
+### 1. Frontend JavaScript Improvements (web_gui.py)
+
+#### Fixed `analyzeData()` function:
+```javascript
+// Before: const sheetFilter = document.getElementById('sheetFilter').value;
+// After: 
+const sheetFilterElement = document.getElementById('sheetFilter');
+const sheetFilter = sheetFilterElement.value || null; // Use null if empty
+```
+
+#### Improved `updateSheetFilter()` function:
+- Added handling for empty sheet lists
+- Added loading state for sheet dropdown
+- Better initialization logic
+
+#### Enhanced page load handling:
+```javascript
+window.onload = function() {
+    // Initialize sheet filter with loading state
+    updateSheetFilter([], null);
+    analyzeData();
+};
+```
+
+### 2. Backend Improvements (web_gui.py)
+
+#### Enhanced request handling:
+```python
+# Handle empty string as None
+if sheet_filter == '' or sheet_filter == 'undefined':
+    sheet_filter = None
+```
+
+#### Added debugging information:
+```python
+# Debug: Print available sheets
+available_sheets = list(comparator_instance.data.keys())
+print(f"Available sheets: {available_sheets}")
+print(f"Requested sheet_filter: {repr(sheet_filter)}")
+```
+
+### 3. Core Logic Improvements (data_comparator.py)
+
+#### Enhanced error handling:
+```python
+# Validate that the requested sheet exists
+if sheet_filter not in sheet_names:
+    raise ValueError(f"Sheet '{sheet_filter}' not found in data. Available sheets: {sheet_names}")
+```
+
+## How It Works Now
+
+1. **Page Load**: 
+   - Sheet dropdown shows "Loading sheets..."
+   - `analyzeData()` is called with `sheet_filter = null`
+
+2. **Backend Processing**:
+   - Loads Excel file and gets available sheet names
+   - If `sheet_filter` is `null` or empty, defaults to first sheet
+   - Validates sheet exists before processing
+
+3. **Response**:
+   - Returns results with `sheet_names` array and `current_sheet_filter`
+   - Frontend populates dropdown with actual sheet names
+   - User can then select different sheets
+
+4. **Sheet Selection**:
+   - User selects different sheet from dropdown
+   - `filterBySheet()` calls `analyzeData()` with selected sheet
+   - Backend processes the specific sheet
+
+## Benefits
+
+✅ **Dynamic**: Works with any Excel file regardless of sheet names
+✅ **Robust**: Handles empty/invalid sheet names gracefully  
+✅ **User-friendly**: Shows available sheets in dropdown
+✅ **Error-resistant**: Provides clear error messages
+✅ **Backward compatible**: Still works with existing functionality
+
+## Test Coverage
+
+Created `test_dynamic_sheets.py` to verify:
+- Default sheet selection (no filter)
+- Each available sheet works
+- Invalid sheet names are handled
+- Empty string sheet names default properly
+
+## Usage Examples
+
+```python
+# Works with any Excel file
+comparator = KSTCoordiComparator("any-file.xlsx")
+comparator.load_data()
+
+# Auto-selects first sheet
+summary = comparator.get_comparison_summary()
+
+# Or specify any existing sheet
+summary = comparator.get_comparison_summary("Sheet1")
+summary = comparator.get_comparison_summary("Data")
+summary = comparator.get_comparison_summary("US URGENT")  # Only if it exists
+```
+
+The application now dynamically adapts to any Excel file structure!
\ No newline at end of file
diff --git a/data/sample-data.xlsx b/data/sample-data.xlsx
index 720976a..8aab366 100644
Binary files a/data/sample-data.xlsx and b/data/sample-data.xlsx differ
diff --git a/data_comparator.py b/data_comparator.py
index 9d79ecb..6653806 100644
--- a/data_comparator.py
+++ b/data_comparator.py
@@ -341,6 +341,10 @@ class KSTCoordiComparator:
         if not sheet_filter:
             raise ValueError("No sheets available or sheet filter not specified")
         
+        # Validate that the requested sheet exists
+        if sheet_filter not in sheet_names:
+            raise ValueError(f"Sheet '{sheet_filter}' not found in data. Available sheets: {sheet_names}")
+        
         # Extract data for the specific sheet only
         sheet_data = self.extract_kst_coordi_items_for_sheet(sheet_filter)
         
diff --git a/templates/index.html b/templates/index.html
index b3d2b00..5961426 100644
--- a/templates/index.html
+++ b/templates/index.html
@@ -390,8 +390,8 @@
                     document.getElementById('filePath').value = data.file_path;
                     statusDiv.innerHTML = '<div class="loading">File uploaded! Analyzing data...</div>';
                     
-                    // Analyze the uploaded file
-                    const sheetFilter = document.getElementById('sheetFilter').value;
+                    // Analyze the uploaded file (use default sheet for new uploads)
+                    const sheetFilter = null; // Always use default (first sheet) for new uploads
                     return fetch('/analyze', {
                         method: 'POST',
                         headers: {
diff --git a/web_gui.py b/web_gui.py
index 50a8783..0510d9f 100644
--- a/web_gui.py
+++ b/web_gui.py
@@ -26,6 +26,10 @@ def analyze_data():
         file_path = request.json.get('file_path', 'data/sample-data.xlsx')
         sheet_filter = request.json.get('sheet_filter', None)
         
+        # Handle empty string as None
+        if sheet_filter == '' or sheet_filter == 'undefined':
+            sheet_filter = None
+        
         if not Path(file_path).exists():
             return jsonify({'error': f'File not found: {file_path}'}), 400
         
@@ -34,6 +38,11 @@ def analyze_data():
         if not comparator_instance.load_data():
             return jsonify({'error': 'Failed to load Excel data'}), 500
         
+        # Debug: Print available sheets
+        available_sheets = list(comparator_instance.data.keys())
+        print(f"Available sheets: {available_sheets}")
+        print(f"Requested sheet_filter: {repr(sheet_filter)}")
+        
         # Get comparison results with optional sheet filtering
         comparison_results = comparator_instance.get_comparison_summary(sheet_filter)
         
@@ -93,6 +102,31 @@ def get_results():
         return jsonify({'error': 'No analysis results available'}), 404
     return jsonify(comparison_results)
 
+@app.route('/get_sheets', methods=['POST'])
+def get_sheets():
+    """Get available sheet names from an Excel file"""
+    try:
+        file_path = request.json.get('file_path', 'data/sample-data.xlsx')
+        
+        if not Path(file_path).exists():
+            return jsonify({'error': f'File not found: {file_path}'}), 400
+        
+        # Create comparator and load data to get sheet names
+        temp_comparator = KSTCoordiComparator(file_path)
+        if not temp_comparator.load_data():
+            return jsonify({'error': 'Failed to load Excel data'}), 500
+        
+        available_sheets = list(temp_comparator.data.keys())
+        
+        return jsonify({
+            'success': True,
+            'sheets': available_sheets,
+            'default_sheet': available_sheets[0] if available_sheets else None
+        })
+        
+    except Exception as e:
+        return jsonify({'error': str(e)}), 500
+
 def create_templates_dir():
     """Create templates directory and HTML file"""
     templates_dir = Path('templates')
@@ -379,7 +413,8 @@ def create_templates_dir():
         
         function analyzeData() {
             const filePath = document.getElementById('filePath').value;
-            const sheetFilter = document.getElementById('sheetFilter').value;
+            const sheetFilterElement = document.getElementById('sheetFilter');
+            const sheetFilter = sheetFilterElement.value || null; // Use null if empty
             const statusDiv = document.getElementById('status');
             const analyzeBtn = document.getElementById('analyzeBtn');
             
@@ -428,6 +463,18 @@ def create_templates_dir():
             const select = document.getElementById('sheetFilter');
             select.innerHTML = '';
             
+            // Add a default option if no sheets are available yet
+            if (!sheetNames || sheetNames.length === 0) {
+                const option = document.createElement('option');
+                option.value = '';
+                option.textContent = 'Loading sheets...';
+                option.disabled = true;
+                option.selected = true;
+                select.appendChild(option);
+                select.disabled = true;
+                return;
+            }
+            
             sheetNames.forEach((sheetName, index) => {
                 const option = document.createElement('option');
                 option.value = sheetName;
@@ -490,8 +537,9 @@ def create_templates_dir():
                     document.getElementById('filePath').value = data.file_path;
                     statusDiv.innerHTML = '<div class="loading">File uploaded! Analyzing data...</div>';
                     
-                    // Analyze the uploaded file
-                    const sheetFilter = document.getElementById('sheetFilter').value;
+                    // Clear sheet filter for new file (let it default to first sheet)
+                    const sheetFilterElement = document.getElementById('sheetFilter');
+                    const sheetFilter = null; // Always use default (first sheet) for new uploads
                     return fetch('/analyze', {
                         method: 'POST',
                         headers: {
@@ -675,6 +723,8 @@ def create_templates_dir():
         
         // Auto-analyze on page load with default file
         window.onload = function() {
+            // Initialize sheet filter with loading state
+            updateSheetFilter([], null);
             analyzeData();
         };
     </script>