diff --git a/cli/src/core/enums.py b/cli/src/core/enums.py
index 9d75892..fc6dae1 100644
--- a/cli/src/core/enums.py
+++ b/cli/src/core/enums.py
@@ -18,3 +18,6 @@ class GuiOption(str, Enum):
     NEW = "new"
     EXISTING = "existing"
     NONE = "none"
+
+    def __str__(self) -> str:
+        return self.value
diff --git a/cli/src/core/exceptions.py b/cli/src/core/exceptions.py
index ba25cd0..fc62f52 100644
--- a/cli/src/core/exceptions.py
+++ b/cli/src/core/exceptions.py
@@ -2,3 +2,9 @@ class UVError(Exception):
     """Raised when running uv yields an exception"""
 
     pass
+
+
+class InvalidCliOptions(Exception):
+    """Raised when running a CLI command with invalid CLI Options"""
+
+    pass
diff --git a/cli/src/models/gui_config.py b/cli/src/models/gui_config.py
index 632c073..5b9d472 100644
--- a/cli/src/models/gui_config.py
+++ b/cli/src/models/gui_config.py
@@ -3,6 +3,7 @@ from typing import Optional
 from pydantic import BaseModel
 
 from core.enums import GuiOption
+from core.exceptions import InvalidCliOptions
 from models import ServiceRegistry
 
 
@@ -22,6 +23,17 @@ class GuiConfig(BaseModel):
 
     def assert_valid(self, service_registry: ServiceRegistry):
         if self.gui_option == GuiOption.EXISTING:
-            service_registry.assert_service_exists(self.ui_filename)
+            if self.raw_ui_filename is None:
+                raise InvalidCliOptions(
+                    f"Must specify --ui-filename when --gui-option is {GuiOption.EXISTING}"
+                )
+            try:
+                service_registry.assert_service_exists(self.ui_filename)
+            except Exception as e:
+                raise InvalidCliOptions(
+                    f"Could not find service with name {self.ui_filename} in service_registry."
+                ) from e
         if self.gui_option == GuiOption.NONE and self.raw_ui_filename:
-            raise ValueError("Cannot specify --ui-filename when --gui-option is 'none'.")
+            raise InvalidCliOptions(
+                f"Cannot specify --ui-filename when --gui-option is {GuiOption.NONE}"
+            )
diff --git a/cli/tests/tests/test_service_creator.py b/cli/tests/tests/test_service_creator.py
index d5d0dd5..8e4c03c 100644
--- a/cli/tests/tests/test_service_creator.py
+++ b/cli/tests/tests/test_service_creator.py
@@ -9,6 +9,7 @@ from pytest_mock import MockerFixture
 from agebd.utils import get_git_root
 from config.paths import Paths
 from core.enums import GuiOption
+from core.exceptions import InvalidCliOptions
 from core.git import GitRepoManager
 from core.service_creator import ServiceCreator
 from models.context import ServicesContext
@@ -99,7 +100,7 @@ def test_raise_if_gui_options_invalid(gui_option, raw_ui_filename, mocker):
 
     gui_config = GuiConfig(gui_option=gui_option, raw_ui_filename=raw_ui_filename)
     creator = ServiceCreator(ctx=ctx, repo_manager=mocker.Mock(spec=GitRepoManager))
-    with pytest.raises(ValueError):
+    with pytest.raises(InvalidCliOptions):
         creator.add_service(
             name="BlaBla",
             ioc_owner="test_user",