diff --git a/tests/test_setup.py b/tests/test_setup.py
index 404fa4c..8ca5f50 100644
--- a/tests/test_setup.py
+++ b/tests/test_setup.py
@@ -1,11 +1,19 @@
-def test_credentials_not_configured_error_exists():
-    from unraid_mcp.core.exceptions import CredentialsNotConfiguredError
+import pytest
 
+from unraid_mcp.core.exceptions import CredentialsNotConfiguredError, ToolError
+
+
+def test_credentials_not_configured_error_exists():
     err = CredentialsNotConfiguredError()
     assert str(err) == "Unraid credentials are not configured."
 
 
 def test_credentials_not_configured_error_is_exception():
-    from unraid_mcp.core.exceptions import CredentialsNotConfiguredError
+    """CredentialsNotConfiguredError must be catchable as a plain Exception."""
+    with pytest.raises(Exception):
+        raise CredentialsNotConfiguredError()
 
-    assert issubclass(CredentialsNotConfiguredError, Exception)
+
+def test_credentials_not_configured_error_is_not_tool_error():
+    """CredentialsNotConfiguredError must NOT be a ToolError — it bypasses MCP protocol error handling."""
+    assert not issubclass(CredentialsNotConfiguredError, ToolError)