diff --git a/selfprivacy_api/graphql/common_types/service.py b/selfprivacy_api/graphql/common_types/service.py
index 680c2a7..5be6d3a 100644
--- a/selfprivacy_api/graphql/common_types/service.py
+++ b/selfprivacy_api/graphql/common_types/service.py
@@ -10,12 +10,6 @@ from selfprivacy_api.services import get_service_by_id, get_services_by_location
 from selfprivacy_api.services import Service as ServiceInterface
 from selfprivacy_api.services import ServiceDnsRecord
 
-from selfprivacy_api.services.config_item import (
-    ServiceConfigItem,
-    StringServiceConfigItem,
-    BoolServiceConfigItem,
-    EnumServiceConfigItem,
-)
 from selfprivacy_api.utils.block_devices import BlockDevices
 from selfprivacy_api.utils.network import get_ip4, get_ip6
 
@@ -147,7 +141,7 @@ def config_item_to_graphql(item: dict) -> ConfigItem:
             type=item_type,
             value=item["value"],
             default_value=item["default_value"],
-            regex=item.get("regex")
+            regex=item.get("regex"),
         )
     elif item_type == "bool":
         return BoolConfigItem(
diff --git a/selfprivacy_api/services/bitwarden/__init__.py b/selfprivacy_api/services/bitwarden/__init__.py
index fc8f309..addf928 100644
--- a/selfprivacy_api/services/bitwarden/__init__.py
+++ b/selfprivacy_api/services/bitwarden/__init__.py
@@ -1,9 +1,7 @@
 """Class representing Bitwarden service"""
 import base64
 import subprocess
-from typing import Optional, List
-
-from selfprivacy_api.utils import get_domain
+from typing import List
 
 from selfprivacy_api.utils.systemd import get_service_status
 from selfprivacy_api.services.service import Service, ServiceStatus
@@ -37,16 +35,6 @@ class Bitwarden(Service):
     def get_user() -> str:
         return "vaultwarden"
 
-    @classmethod
-    def get_url(cls) -> Optional[str]:
-        """Return service url."""
-        domain = get_domain()
-        return f"https://password.{domain}"
-
-    @classmethod
-    def get_subdomain(cls) -> Optional[str]:
-        return "password"
-
     @staticmethod
     def is_movable() -> bool:
         return True
diff --git a/selfprivacy_api/services/config_item.py b/selfprivacy_api/services/config_item.py
index 90f0ed7..abddd46 100644
--- a/selfprivacy_api/services/config_item.py
+++ b/selfprivacy_api/services/config_item.py
@@ -2,6 +2,8 @@ from abc import ABC, abstractmethod
 import re
 from typing import Optional
 
+from selfprivacy_api.utils import check_if_subdomain_is_taken
+
 
 class ServiceConfigItem(ABC):
     id: str
@@ -17,6 +19,10 @@ class ServiceConfigItem(ABC):
     def set_value(self, value, service_options):
         pass
 
+    @abstractmethod
+    def validate_value(self, value):
+        return True
+
     def as_dict(self, service_options):
         return {
             "id": self.id,
@@ -35,18 +41,24 @@ class StringServiceConfigItem(ServiceConfigItem):
         description: str,
         regex: Optional[str] = None,
         widget: Optional[str] = None,
+        allow_empty: bool = False,
     ):
+        if widget == "subdomain" and not regex:
+            raise ValueError("Subdomain widget requires regex")
         self.id = id
         self.type = "string"
         self.default_value = default_value
         self.description = description
         self.regex = re.compile(regex) if regex else None
         self.widget = widget if widget else "text"
+        self.allow_empty = allow_empty
 
     def get_value(self, service_options):
         return service_options.get(self.id, self.default_value)
 
     def set_value(self, value, service_options):
+        if not self.validate_value(value):
+            raise ValueError(f"Value {value} is not valid")
         if self.regex and not self.regex.match(value):
             raise ValueError(f"Value {value} does not match regex {self.regex}")
         service_options[self.id] = value
@@ -62,6 +74,18 @@ class StringServiceConfigItem(ServiceConfigItem):
             "regex": self.regex.pattern if self.regex else None,
         }
 
+    def validate_value(self, value):
+        if not isinstance(value, str):
+            return False
+        if not self.allow_empty and not value:
+            return False
+        if self.regex and not self.regex.match(value):
+            return False
+        if self.widget == "subdomain":
+            if check_if_subdomain_is_taken(value):
+                return False
+        return True
+
 
 class BoolServiceConfigItem(ServiceConfigItem):
     def __init__(
@@ -81,6 +105,8 @@ class BoolServiceConfigItem(ServiceConfigItem):
         return service_options.get(self.id, self.default_value)
 
     def set_value(self, value, service_options):
+        if not isinstance(value, bool):
+            raise ValueError(f"Value {value} is not a boolean")
         service_options[self.id] = value
 
     def as_dict(self, service_options):
@@ -93,6 +119,9 @@ class BoolServiceConfigItem(ServiceConfigItem):
             "default_value": self.default_value,
         }
 
+    def validate_value(self, value):
+        return isinstance(value, bool)
+
 
 class EnumServiceConfigItem(ServiceConfigItem):
     def __init__(
@@ -114,6 +143,8 @@ class EnumServiceConfigItem(ServiceConfigItem):
         return service_options.get(self.id, self.default_value)
 
     def set_value(self, value, service_options):
+        if not self.validate_value(value):
+            raise ValueError(f"Value {value} is not valid")
         if value not in self.options:
             raise ValueError(f"Value {value} not in options {self.options}")
         service_options[self.id] = value
@@ -129,6 +160,11 @@ class EnumServiceConfigItem(ServiceConfigItem):
             "options": self.options,
         }
 
+    def validate_value(self, value):
+        if not isinstance(value, str):
+            return False
+        return value in self.options
+
 
 # TODO: unused for now
 class IntServiceConfigItem(ServiceConfigItem):
@@ -156,7 +192,9 @@ class IntServiceConfigItem(ServiceConfigItem):
         if self.min_value is not None and value < self.min_value:
             raise ValueError(f"Value {value} is less than min_value {self.min_value}")
         if self.max_value is not None and value > self.max_value:
-            raise ValueError(f"Value {value} is greater than max_value {self.max_value}")
+            raise ValueError(
+                f"Value {value} is greater than max_value {self.max_value}"
+            )
         service_options[self.id] = value
 
     def as_dict(self, service_options):
@@ -170,3 +208,10 @@ class IntServiceConfigItem(ServiceConfigItem):
             "min_value": self.min_value,
             "max_value": self.max_value,
         }
+
+    def validate_value(self, value):
+        if not isinstance(value, int):
+            return False
+        return (self.min_value is None or value >= self.min_value) and (
+            self.max_value is None or value <= self.max_value
+        )
diff --git a/selfprivacy_api/services/forgejo/__init__.py b/selfprivacy_api/services/forgejo/__init__.py
index ff6d12c..8c6ef4f 100644
--- a/selfprivacy_api/services/forgejo/__init__.py
+++ b/selfprivacy_api/services/forgejo/__init__.py
@@ -1,9 +1,9 @@
 """Class representing Bitwarden service"""
 import base64
 import subprocess
-from typing import Optional, List
+from typing import List
 
-from selfprivacy_api.utils import get_domain, ReadUserData, WriteUserData
+from selfprivacy_api.utils import ReadUserData, WriteUserData
 
 from selfprivacy_api.utils.systemd import get_service_status
 from selfprivacy_api.services.service import Service, ServiceStatus
@@ -14,6 +14,7 @@ from selfprivacy_api.services.config_item import (
     EnumServiceConfigItem,
     ServiceConfigItem,
 )
+from selfprivacy_api.utils.regex_strings import SUBDOMAIN_REGEX
 
 
 class Forgejo(Service):
@@ -27,7 +28,7 @@ class Forgejo(Service):
             id="subdomain",
             default_value="git",
             description="Subdomain",
-            regex=r"^[A-Za-z0-9][A-Za-z0-9\-]{0,61}[A-Za-z0-9]$",
+            regex=SUBDOMAIN_REGEX,
             widget="subdomain",
         ),
         "appName": StringServiceConfigItem(
@@ -90,21 +91,6 @@ class Forgejo(Service):
         """Read SVG icon from file and return it as base64 encoded string."""
         return base64.b64encode(FORGEJO_ICON.encode("utf-8")).decode("utf-8")
 
-    @classmethod
-    def get_url(cls) -> Optional[str]:
-        """Return service url."""
-        domain = get_domain()
-        subdomain = cls.get_subdomain()
-        return f"https://{subdomain}.{domain}"
-
-    @classmethod
-    def get_subdomain(cls) -> Optional[str]:
-        with ReadUserData() as data:
-            if "gitea" in data["modules"]:
-                return data["modules"]["gitea"]["subdomain"]
-
-        return "git"
-
     @staticmethod
     def is_movable() -> bool:
         return True
diff --git a/selfprivacy_api/services/jitsimeet/__init__.py b/selfprivacy_api/services/jitsimeet/__init__.py
index 1df7c2a..08462e0 100644
--- a/selfprivacy_api/services/jitsimeet/__init__.py
+++ b/selfprivacy_api/services/jitsimeet/__init__.py
@@ -1,14 +1,13 @@
 """Class representing Jitsi Meet service"""
 import base64
 import subprocess
-from typing import Optional, List
+from typing import List
 
 from selfprivacy_api.jobs import Job
 from selfprivacy_api.utils.systemd import (
     get_service_status_from_several_units,
 )
 from selfprivacy_api.services.service import Service, ServiceStatus
-from selfprivacy_api.utils import get_domain
 from selfprivacy_api.utils.block_devices import BlockDevice
 from selfprivacy_api.services.jitsimeet.icon import JITSI_ICON
 
@@ -36,16 +35,6 @@ class JitsiMeet(Service):
         """Read SVG icon from file and return it as base64 encoded string."""
         return base64.b64encode(JITSI_ICON.encode("utf-8")).decode("utf-8")
 
-    @classmethod
-    def get_url(cls) -> Optional[str]:
-        """Return service url."""
-        domain = get_domain()
-        return f"https://meet.{domain}"
-
-    @classmethod
-    def get_subdomain(cls) -> Optional[str]:
-        return "meet"
-
     @staticmethod
     def is_movable() -> bool:
         return False
diff --git a/selfprivacy_api/services/nextcloud/__init__.py b/selfprivacy_api/services/nextcloud/__init__.py
index 43caecd..14ea078 100644
--- a/selfprivacy_api/services/nextcloud/__init__.py
+++ b/selfprivacy_api/services/nextcloud/__init__.py
@@ -1,9 +1,7 @@
 """Class representing Nextcloud service."""
 import base64
 import subprocess
-from typing import Optional, List
-
-from selfprivacy_api.utils import get_domain
+from typing import List
 
 from selfprivacy_api.utils.systemd import get_service_status
 from selfprivacy_api.services.service import Service, ServiceStatus
@@ -34,16 +32,6 @@ class Nextcloud(Service):
         """Read SVG icon from file and return it as base64 encoded string."""
         return base64.b64encode(NEXTCLOUD_ICON.encode("utf-8")).decode("utf-8")
 
-    @classmethod
-    def get_url(cls) -> Optional[str]:
-        """Return service url."""
-        domain = get_domain()
-        return f"https://cloud.{domain}"
-
-    @classmethod
-    def get_subdomain(cls) -> Optional[str]:
-        return "cloud"
-
     @staticmethod
     def is_movable() -> bool:
         return True
diff --git a/selfprivacy_api/services/ocserv/__init__.py b/selfprivacy_api/services/ocserv/__init__.py
index e7f3ffd..818b1d8 100644
--- a/selfprivacy_api/services/ocserv/__init__.py
+++ b/selfprivacy_api/services/ocserv/__init__.py
@@ -33,10 +33,6 @@ class Ocserv(Service):
         """Return service url."""
         return None
 
-    @classmethod
-    def get_subdomain(cls) -> typing.Optional[str]:
-        return "vpn"
-
     @staticmethod
     def is_movable() -> bool:
         return False
diff --git a/selfprivacy_api/services/pleroma/__init__.py b/selfprivacy_api/services/pleroma/__init__.py
index 8367901..e300844 100644
--- a/selfprivacy_api/services/pleroma/__init__.py
+++ b/selfprivacy_api/services/pleroma/__init__.py
@@ -1,9 +1,7 @@
 """Class representing Nextcloud service."""
 import base64
 import subprocess
-from typing import Optional, List
-
-from selfprivacy_api.utils import get_domain
+from typing import List
 
 from selfprivacy_api.services.owned_path import OwnedPath
 from selfprivacy_api.utils.systemd import get_service_status
@@ -31,16 +29,6 @@ class Pleroma(Service):
     def get_svg_icon() -> str:
         return base64.b64encode(PLEROMA_ICON.encode("utf-8")).decode("utf-8")
 
-    @classmethod
-    def get_url(cls) -> Optional[str]:
-        """Return service url."""
-        domain = get_domain()
-        return f"https://social.{domain}"
-
-    @classmethod
-    def get_subdomain(cls) -> Optional[str]:
-        return "social"
-
     @staticmethod
     def is_movable() -> bool:
         return True
diff --git a/selfprivacy_api/services/roundcube/__init__.py b/selfprivacy_api/services/roundcube/__init__.py
index 22604f5..2493c87 100644
--- a/selfprivacy_api/services/roundcube/__init__.py
+++ b/selfprivacy_api/services/roundcube/__init__.py
@@ -2,14 +2,13 @@
 
 import base64
 import subprocess
-from typing import List, Optional
+from typing import List
 
 from selfprivacy_api.jobs import Job
 from selfprivacy_api.utils.systemd import (
     get_service_status_from_several_units,
 )
 from selfprivacy_api.services.service import Service, ServiceStatus
-from selfprivacy_api.utils import ReadUserData, get_domain
 from selfprivacy_api.utils.block_devices import BlockDevice
 from selfprivacy_api.services.roundcube.icon import ROUNDCUBE_ICON
 
@@ -37,21 +36,6 @@ class Roundcube(Service):
         """Read SVG icon from file and return it as base64 encoded string."""
         return base64.b64encode(ROUNDCUBE_ICON.encode("utf-8")).decode("utf-8")
 
-    @classmethod
-    def get_url(cls) -> Optional[str]:
-        """Return service url."""
-        domain = get_domain()
-        subdomain = cls.get_subdomain()
-        return f"https://{subdomain}.{domain}"
-
-    @classmethod
-    def get_subdomain(cls) -> Optional[str]:
-        with ReadUserData() as data:
-            if "roundcube" in data["modules"]:
-                return data["modules"]["roundcube"]["subdomain"]
-
-        return "roundcube"
-
     @staticmethod
     def is_movable() -> bool:
         return False
diff --git a/selfprivacy_api/services/service.py b/selfprivacy_api/services/service.py
index e199346..ba1ba10 100644
--- a/selfprivacy_api/services/service.py
+++ b/selfprivacy_api/services/service.py
@@ -1,9 +1,10 @@
 """Abstract class for a service running on a server"""
 from abc import ABC, abstractmethod
-from typing import Any, List, Optional
+from typing import List, Optional
 
 from selfprivacy_api import utils
-from selfprivacy_api.utils import ReadUserData, WriteUserData
+from selfprivacy_api.utils.default_subdomains import DEFAULT_SUBDOMAINS
+from selfprivacy_api.utils import ReadUserData, WriteUserData, get_domain
 from selfprivacy_api.utils.waitloop import wait_until_true
 from selfprivacy_api.utils.block_devices import BlockDevice, BlockDevices
 
@@ -66,20 +67,27 @@ class Service(ABC):
         pass
 
     @classmethod
-    @abstractmethod
     def get_url(cls) -> Optional[str]:
         """
         The url of the service if it is accessible from the internet browser.
         """
-        pass
+        domain = get_domain()
+        subdomain = cls.get_subdomain()
+        return f"https://{subdomain}.{domain}"
 
     @classmethod
-    @abstractmethod
     def get_subdomain(cls) -> Optional[str]:
         """
         The assigned primary subdomain for this service.
         """
-        pass
+        name = cls.get_id()
+        with ReadUserData() as user_data:
+            if "modules" in user_data:
+                if name in user_data["modules"]:
+                    if "subdomain" in user_data["modules"][name]:
+                        return user_data["modules"][name]["subdomain"]
+
+        return DEFAULT_SUBDOMAINS.get(name)
 
     @classmethod
     def get_user(cls) -> Optional[str]:
diff --git a/selfprivacy_api/services/test_service/__init__.py b/selfprivacy_api/services/test_service/__init__.py
index b808ac6..1a2fd9d 100644
--- a/selfprivacy_api/services/test_service/__init__.py
+++ b/selfprivacy_api/services/test_service/__init__.py
@@ -1,6 +1,5 @@
 """Class representing Bitwarden service"""
 import base64
-import typing
 import subprocess
 
 from typing import List
@@ -57,16 +56,6 @@ class DummyService(Service):
         # return ""
         return base64.b64encode(BITWARDEN_ICON.encode("utf-8")).decode("utf-8")
 
-    @classmethod
-    def get_url(cls) -> typing.Optional[str]:
-        """Return service url."""
-        domain = "test.com"
-        return f"https://password.{domain}"
-
-    @classmethod
-    def get_subdomain(cls) -> typing.Optional[str]:
-        return "password"
-
     @classmethod
     def is_movable(cls) -> bool:
         return cls.movable
diff --git a/selfprivacy_api/utils/__init__.py b/selfprivacy_api/utils/__init__.py
index 779bdf6..9972ff2 100644
--- a/selfprivacy_api/utils/__init__.py
+++ b/selfprivacy_api/utils/__init__.py
@@ -8,6 +8,11 @@ import subprocess
 import portalocker
 import typing
 
+from selfprivacy_api.utils.default_subdomains import (
+    DEFAULT_SUBDOMAINS,
+    RESERVED_SUBDOMAINS,
+)
+
 
 USERDATA_FILE = "/etc/nixos/userdata.json"
 SECRETS_FILE = "/etc/selfprivacy/secrets.json"
@@ -133,6 +138,20 @@ def is_username_forbidden(username):
     return False
 
 
+def check_if_subdomain_is_taken(subdomain: str) -> bool:
+    """Check if subdomain is already taken or reserved"""
+    if subdomain in RESERVED_SUBDOMAINS:
+        return True
+    with ReadUserData() as data:
+        for module in data["modules"]:
+            if (
+                data["modules"][module].get("subdomain", DEFAULT_SUBDOMAINS[module])
+                == subdomain
+            ):
+                return True
+    return False
+
+
 def parse_date(date_str: str) -> datetime.datetime:
     """Parse date string which can be in one of these formats:
     - %Y-%m-%dT%H:%M:%S.%fZ
diff --git a/selfprivacy_api/utils/default_subdomains.py b/selfprivacy_api/utils/default_subdomains.py
new file mode 100644
index 0000000..f6665fc
--- /dev/null
+++ b/selfprivacy_api/utils/default_subdomains.py
@@ -0,0 +1,21 @@
+DEFAULT_SUBDOMAINS = {
+    "bitwarden": "password",
+    "gitea": "git",
+    "jitsi-meet": "meet",
+    "simple-nixos-mailserver": "",
+    "nextcloud": "cloud",
+    "ocserv": "vpn",
+    "pleroma": "social",
+    "roundcube": "roundcube",
+    "testservice": "test",
+}
+
+RESERVED_SUBDOMAINS = [
+    "admin",
+    "administrator",
+    "api",
+    "auth",
+    "user",
+    "users",
+    "ntfy",
+]
diff --git a/selfprivacy_api/utils/regex_strings.py b/selfprivacy_api/utils/regex_strings.py
new file mode 100644
index 0000000..718e2ab
--- /dev/null
+++ b/selfprivacy_api/utils/regex_strings.py
@@ -0,0 +1 @@
+SUBDOMAIN_REGEX = r"^[A-Za-z0-9][A-Za-z0-9\-]{0,61}[A-Za-z0-9]$"
diff --git a/tests/test_config_item.py b/tests/test_config_item.py
new file mode 100644
index 0000000..724c29e
--- /dev/null
+++ b/tests/test_config_item.py
@@ -0,0 +1,157 @@
+import pytest
+from selfprivacy_api.services.config_item import (
+    StringServiceConfigItem,
+    BoolServiceConfigItem,
+    EnumServiceConfigItem,
+)
+from selfprivacy_api.utils.regex_strings import SUBDOMAIN_REGEX
+
+
+@pytest.fixture
+def service_options():
+    return {}
+
+
+def test_string_service_config_item(service_options):
+    item = StringServiceConfigItem(
+        id="test_string",
+        default_value="1337",
+        description="Test digits string",
+        regex=r"^\d+$",
+        widget="text",
+        allow_empty=False,
+    )
+    assert item.get_value(service_options) == "1337"
+    item.set_value("123", service_options)
+    assert item.get_value(service_options) == "123"
+    with pytest.raises(ValueError):
+        item.set_value("abc", service_options)
+    assert item.validate_value("123") is True
+    assert item.validate_value("abc") is False
+    assert item.validate_value("123abc") is False
+    assert item.validate_value("") is False
+    assert item.validate_value(None) is False
+    assert item.validate_value(123) is False
+    assert item.validate_value("123.0") is False
+    assert item.validate_value(True) is False
+
+
+def test_string_service_config_item_allows_empty(service_options):
+    item = StringServiceConfigItem(
+        id="test_string",
+        default_value="1337",
+        description="Test digits string",
+        widget="text",
+        allow_empty=True,
+    )
+    assert item.get_value(service_options) == "1337"
+    item.set_value("", service_options)
+    assert item.get_value(service_options) == ""
+    assert item.validate_value("") is True
+    assert item.validate_value(None) is False
+    assert item.validate_value(123) is False
+    assert item.validate_value("123") is True
+    assert item.validate_value("abc") is True
+    assert item.validate_value("123abc") is True
+    assert item.validate_value("123.0") is True
+    assert item.validate_value(True) is False
+
+
+def test_string_service_config_item_not_allows_empty(service_options):
+    item = StringServiceConfigItem(
+        id="test_string",
+        default_value="1337",
+        description="Test digits string",
+        widget="text",
+    )
+    assert item.get_value(service_options) == "1337"
+    with pytest.raises(ValueError):
+        item.set_value("", service_options)
+    assert item.get_value(service_options) == "1337"
+    assert item.validate_value("") is False
+    assert item.validate_value(None) is False
+    assert item.validate_value(123) is False
+    assert item.validate_value("123") is True
+    assert item.validate_value("abc") is True
+    assert item.validate_value("123abc") is True
+    assert item.validate_value("123.0") is True
+    assert item.validate_value(True) is False
+
+
+def test_bool_service_config_item(service_options):
+    item = BoolServiceConfigItem(
+        id="test_bool",
+        default_value=True,
+        description="Test bool",
+        widget="switch",
+    )
+    assert item.get_value(service_options) is True
+    item.set_value(False, service_options)
+    assert item.get_value(service_options) is False
+    assert item.validate_value(True) is True
+    assert item.validate_value(False) is True
+    assert item.validate_value("True") is False
+    assert item.validate_value("False") is False
+    assert item.validate_value(1) is False
+    assert item.validate_value(0) is False
+    assert item.validate_value("1") is False
+
+
+def test_enum_service_config_item(service_options):
+    item = EnumServiceConfigItem(
+        id="test_enum",
+        default_value="option1",
+        description="Test enum",
+        options=["option1", "option2", "option3"],
+        widget="select",
+    )
+    assert item.get_value(service_options) == "option1"
+    item.set_value("option2", service_options)
+    assert item.get_value(service_options) == "option2"
+    with pytest.raises(ValueError):
+        item.set_value("option4", service_options)
+    assert item.validate_value("option1") is True
+    assert item.validate_value("option4") is False
+    assert item.validate_value("option2") is True
+    assert item.validate_value(1) is False
+    assert item.validate_value("1") is False
+    assert item.validate_value(True) is False
+
+
+def test_string_service_config_item_subdomain(service_options, dummy_service):
+    item = StringServiceConfigItem(
+        id="test_subdomain",
+        default_value="example",
+        description="Test subdomain string",
+        widget="subdomain",
+        allow_empty=False,
+        regex=SUBDOMAIN_REGEX,
+    )
+    assert item.get_value(service_options) == "example"
+    item.set_value("subdomain", service_options)
+    assert item.get_value(service_options) == "subdomain"
+    with pytest.raises(ValueError):
+        item.set_value(
+            "invalid-subdomain-because-it-is-very-very-very-very-very-very-long",
+            service_options,
+        )
+    assert item.validate_value("subdomain") is True
+    assert (
+        item.validate_value(
+            "invalid-subdomain-because-it-is-very-very-very-very-very-very-long"
+        )
+        is False
+    )
+    assert item.validate_value("api") is False
+    assert item.validate_value("auth") is False
+    assert item.validate_value("user") is False
+    assert item.validate_value("users") is False
+    assert item.validate_value("ntfy") is False
+    assert item.validate_value("") is False
+    assert item.validate_value(None) is False
+    assert item.validate_value(123) is False
+    assert item.validate_value("123") is True
+    assert item.validate_value("abc") is True
+    assert item.validate_value("123abc") is True
+    assert item.validate_value("123.0") is False
+    assert item.validate_value(True) is False
diff --git a/tests/test_graphql/test_services.py b/tests/test_graphql/test_services.py
index b7faf3d..b349f53 100644
--- a/tests/test_graphql/test_services.py
+++ b/tests/test_graphql/test_services.py
@@ -188,6 +188,7 @@ allServices {
     id
     status
     isEnabled
+    url
 }
 """
 
@@ -347,6 +348,7 @@ def test_get_services(authorized_client, only_dummy_service):
     assert api_dummy_service["id"] == "testservice"
     assert api_dummy_service["status"] == ServiceStatus.ACTIVE.value
     assert api_dummy_service["isEnabled"] is True
+    assert api_dummy_service["url"] == "https://test.test-domain.tld"
 
 
 def test_enable_return_value(authorized_client, only_dummy_service):