diff --git a/src/hosts/core/manager.py b/src/hosts/core/manager.py
index e3951e4..a1230fe 100644
--- a/src/hosts/core/manager.py
+++ b/src/hosts/core/manager.py
@@ -296,7 +296,18 @@ class HostsManager:
         try:
             # Add the new entry at the end
             hosts_file.entries.append(entry)
-            return True, "Entry added successfully"
+
+            # Save the file immediately
+            save_success, save_message = self.save_hosts_file(hosts_file)
+            if not save_success:
+                # If save fails, remove the entry that was just added
+                hosts_file.entries.pop()
+                return False, f"Failed to save after adding entry: {save_message}"
+
+            canonical_hostname = (
+                entry.hostnames[0] if entry.hostnames else entry.ip_address
+            )
+            return True, f"Entry added: {canonical_hostname}"
 
         except Exception as e:
             return False, f"Error adding entry: {e}"
diff --git a/src/hosts/tui/app.py b/src/hosts/tui/app.py
index 270d707..520dfdb 100644
--- a/src/hosts/tui/app.py
+++ b/src/hosts/tui/app.py
@@ -7,7 +7,7 @@ all the handlers and provides the primary user interface.
 
 from textual.app import App, ComposeResult
 from textual.containers import Horizontal, Vertical
-from textual.widgets import Header, Static, DataTable, Input, Checkbox, Label
+from textual.widgets import Header, Static, DataTable, Input, Checkbox
 from textual.reactive import reactive
 
 from ..core.parser import HostsParser
@@ -94,7 +94,9 @@ class HostsManagerApp(App):
 
                 # Details display form (disabled inputs)
                 with Vertical(id="entry-details-display", classes="entry-form"):
-                    with Vertical(classes="default-section section-no-top-margin") as ip_address:
+                    with Vertical(
+                        classes="default-section section-no-top-margin"
+                    ) as ip_address:
                         ip_address.border_title = "IP Address"
                         yield Input(
                             placeholder="No entry selected",
@@ -118,18 +120,23 @@ class HostsManagerApp(App):
                             placeholder="No entry selected",
                             id="details-comment-input",
                             disabled=True,
-                        classes="default-input",
-                    )
+                            classes="default-input",
+                        )
 
                     with Vertical(classes="default-section") as active:
                         active.border_title = "Active"
                         yield Checkbox(
-                            "Active", id="details-active-checkbox", disabled=True, classes="default-checkbox"
+                            "Active",
+                            id="details-active-checkbox",
+                            disabled=True,
+                            classes="default-checkbox",
                         )
 
                 # Edit form (initially hidden)
                 with Vertical(id="entry-edit-form", classes="entry-form hidden"):
-                    with Vertical(classes="default-section section-no-top-margin") as ip_address:
+                    with Vertical(
+                        classes="default-section section-no-top-margin"
+                    ) as ip_address:
                         ip_address.border_title = "IP Address"
                         yield Input(
                             placeholder="Enter IP address",
@@ -151,11 +158,13 @@ class HostsManagerApp(App):
                             placeholder="Enter comment (optional)",
                             id="comment-input",
                             classes="default-input",
-                    )
+                        )
 
                     with Vertical(classes="default-section") as active:
                         active.border_title = "Active"
-                        yield Checkbox("Active", id="active-checkbox", classes="default-checkbox")
+                        yield Checkbox(
+                            "Active", id="active-checkbox", classes="default-checkbox"
+                        )
 
         # Status bar for error/temporary messages (overlay, doesn't affect layout)
         yield Static("", id="status-bar", classes="status-bar hidden")
diff --git a/tests/test_manager.py b/tests/test_manager.py
index c1d0657..ae5f6c0 100644
--- a/tests/test_manager.py
+++ b/tests/test_manager.py
@@ -634,3 +634,58 @@ class TestHostsManager:
         finally:
             # Clean up
             Path(temp_path).unlink()
+
+    def test_add_entry_success(self):
+        """Test successfully adding an entry with immediate save."""
+        manager = HostsManager()
+        manager.edit_mode = True
+
+        # Mock the save operation to succeed
+        with patch.object(manager, "save_hosts_file") as mock_save:
+            mock_save.return_value = (True, "File saved successfully")
+
+            hosts_file = HostsFile()
+            test_entry = HostEntry(ip_address="192.168.1.100", hostnames=["testhost"])
+
+            success, message = manager.add_entry(hosts_file, test_entry)
+
+            assert success
+            assert "Entry added: testhost" in message
+            assert len(hosts_file.entries) == 1
+            assert hosts_file.entries[0] == test_entry
+            mock_save.assert_called_once_with(hosts_file)
+
+    def test_add_entry_save_failure(self):
+        """Test adding an entry when save fails."""
+        manager = HostsManager()
+        manager.edit_mode = True
+
+        # Mock the save operation to fail
+        with patch.object(manager, "save_hosts_file") as mock_save:
+            mock_save.return_value = (False, "Permission denied")
+
+            hosts_file = HostsFile()
+            test_entry = HostEntry(ip_address="192.168.1.100", hostnames=["testhost"])
+
+            success, message = manager.add_entry(hosts_file, test_entry)
+
+            assert not success
+            assert "Failed to save after adding entry" in message
+            assert (
+                len(hosts_file.entries) == 0
+            )  # Entry should be removed on save failure
+            mock_save.assert_called_once_with(hosts_file)
+
+    def test_add_entry_not_in_edit_mode(self):
+        """Test adding an entry when not in edit mode."""
+        manager = HostsManager()
+        # edit_mode defaults to False
+
+        hosts_file = HostsFile()
+        test_entry = HostEntry(ip_address="192.168.1.100", hostnames=["testhost"])
+
+        success, message = manager.add_entry(hosts_file, test_entry)
+
+        assert not success
+        assert "Not in edit mode" in message
+        assert len(hosts_file.entries) == 0