diff --git a/functions/process_csv.py b/functions/process_csv.py
index ee96241..c3155cd 100644
--- a/functions/process_csv.py
+++ b/functions/process_csv.py
@@ -3,7 +3,15 @@ from io import TextIOWrapper
 from config import item_attributes
 
 def get_csv_data(file):
+    """Extract and validate CSV data."""
     csv_file = TextIOWrapper(file, encoding='utf-8')
+
+    # Check delimiter
+    sample = csv_file.read(1024)
+    csv_file.seek(0)
+    if '|' not in sample:
+        raise ValueError("CSV file must use '|' as the delimiter.")
+
     reader = csv.DictReader(csv_file, delimiter='|')
 
     # Validate CSV headers based on config
diff --git a/routes/upload.py b/routes/upload.py
index 0598285..02c8aeb 100644
--- a/routes/upload.py
+++ b/routes/upload.py
@@ -1,6 +1,7 @@
-from flask import Blueprint, request, render_template, redirect, session
+from flask import Blueprint, request, render_template, redirect, session, flash
 from definitions.models import Asset, db
 from functions.process_csv import get_csv_data
+from functions.validate_values import validate_values
 from config import item_attributes
 
 upload_bp = Blueprint('uploadcsv', __name__)
@@ -10,26 +11,39 @@ def upload_file():
     if request.method == 'POST':
         # Check if a file was uploaded
         if 'file' not in request.files:
-            return redirect('uploadcsv')
+            flash("No file uploaded.", "error")
+            return redirect(request.url)
 
         file = request.files['file']
 
         # Check if the file is a CSV
         if file.filename == '' or not file.filename.endswith('.csv'):
-            return redirect('uploadcsv')
+            flash("Please upload a valid CSV file.", "error")
+            return redirect(request.url)
 
         try:
-            # Extract data from the CSV file
+            # Extract and validate CSV data
             csvdata = get_csv_data(file)
 
-            # Identify the primary attribute
-            primary_attrib = next(
-                (attrib for attrib in item_attributes if attrib.primary),
-                None
-            )
+            # Validate each row of data
+            errors = []
+            for i, row in enumerate(csvdata, start=1):
+                error = validate_values(row)
+                if error:
+                    errors.append(f"Row {i}: {error}")
 
+            if errors:
+                # Pass errors as a list to the template
+                return render_template(
+                    'upload.html',
+                    errors=errors
+                )
+
+            # Identify the primary attribute
+            primary_attrib = next((attrib for attrib in item_attributes if attrib.primary), None)
             if not primary_attrib:
-                return "Primary attribute not defined in configuration."
+                flash("Primary attribute not defined in configuration.", "error")
+                return redirect(request.url)
 
             # Separate new and existing assets
             new_assets = []
@@ -54,8 +68,8 @@ def upload_file():
 
         except Exception as e:
             # Handle errors during file processing
-            print(f"Error processing CSV file: {str(e)}")
-            return redirect('uploadcsv')
+            flash(f"Error processing CSV file: {str(e)}", "error")
+            return redirect(request.url)
 
     # Render the upload page for GET requests
     return render_template('upload.html')
\ No newline at end of file
diff --git a/templates/csv_preview.html b/templates/csv_preview.html
index d73a2f0..ee8159a 100644
--- a/templates/csv_preview.html
+++ b/templates/csv_preview.html
@@ -9,50 +9,35 @@
 <body>
     <h1>CSV Preview</h1>
 
-    <!-- Display CSV data in a table -->
-    {% if new_assets %}
-    <p>New assets:</p>
-    <table border="1" class="table-new-assets">
-        <thead>
-            <tr>
-                {% for attrib in item_attributes %}
-                    <th data-attrib="{{ attrib.attrib_name }}">{{ attrib.display_name }}</th>
-                {% endfor %}
-            </tr>
-        </thead>
-        <tbody>
-            {% for asset in new_assets %}
-                <tr>
-                    {% for attrib in item_attributes %}
-                        <td contenteditable="true">{{ asset[attrib.attrib_name] }}</td>
+    <!-- Render tables for new and existing assets -->
+    {% for table_name, assets, editable in [
+        ('New Assets', new_assets, true),
+        ('Existing Assets', existing, false)
+    ] %}
+        {% if assets %}
+            <h2>{{ table_name }}</h2>
+            <table border="1" class="table-new-assets">
+                <thead>
+                    <tr>
+                        {% for attrib in item_attributes %}
+                            <th data-attrib="{{ attrib.attrib_name }}">{{ attrib.display_name }}</th>
+                        {% endfor %}
+                    </tr>
+                </thead>
+                <tbody>
+                    {% for asset in assets %}
+                        <tr>
+                            {% for attrib in item_attributes %}
+                                <td {% if editable %}contenteditable="true"{% endif %}>
+                                    {{ asset[attrib.attrib_name] }}
+                                </td>
+                            {% endfor %}
+                        </tr>
                     {% endfor %}
-                </tr>
-            {% endfor %}
-        </tbody>
-    </table>
-    {% endif %}
-
-    {% if existing %}
-    <p>These assets are already in the database:</p>
-    <table border="1" class="table-existing-assets">
-        <thead>
-            <tr>
-                {% for attrib in item_attributes %}
-                    <th>{{ attrib.display_name }}</th>
-                {% endfor %}
-            </tr>
-        </thead>
-        <tbody>
-            {% for asset in existing %}
-                <tr>
-                    {% for attrib in item_attributes %}
-                        <td>{{ asset[attrib.attrib_name] }}</td>
-                    {% endfor %}
-                </tr>
-            {% endfor %}
-        </tbody>
-    </table>
-    {% endif %}
+                </tbody>
+            </table>
+        {% endif %}
+    {% endfor %}
 
     <!-- Form button to confirm and save data -->
     {% if new_assets %}
diff --git a/templates/upload.html b/templates/upload.html
index 66887ca..d128491 100644
--- a/templates/upload.html
+++ b/templates/upload.html
@@ -7,15 +7,36 @@
 </head>
 <body>
     <h1>Upload CSV File</h1>
+
+    <!-- Display flash messages -->
+    {% with messages = get_flashed_messages(with_categories=true) %}
+        {% if messages %}
+            {% for category, message in messages %}
+                <p style="color: red;">{{ message }}</p>
+            {% endfor %}
+        {% endif %}
+    {% endwith %}
+
+    <!-- Display validation errors if any -->
+    {% if errors %}
+        <details style="margin-bottom: 20px;">
+            <summary style="color: red; font-weight: bold;">
+                Errors found in the CSV file (click to expand):
+            </summary>
+            <ul>
+                {% for error in errors %}
+                    <li>{{ error }}</li>
+                {% endfor %}
+            </ul>
+        </details>
+    {% endif %}
+
+    <!-- Upload form -->
     <form action="/uploadcsv" method="POST" enctype="multipart/form-data">
         <label for="file">Choose a CSV file:</label>
         <input type="file" id="file" name="file" accept=".csv" required>
         <br><br>
         <button type="submit">Upload</button>
     </form>
-
-    {% if error %}
-        <p style="color: red;">{{ error }}</p>
-    {% endif %}
 </body>
 </html>
\ No newline at end of file
